Libc-498.1.1.tar.gz

[apple/libc.git] / gen / scalable_malloc.c

/*
 * Copyright (c) 1999, 2006 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

/* Author: Bertrand Serlet, August 1999 */

#include "scalable_malloc.h"
#include "malloc_printf.h"
#include "_simple.h"

#include <pthread_internals.h>

#include <unistd.h>
#include <libc.h>
#include <mach/vm_statistics.h>
#include <mach/mach_init.h>
#include <sys/types.h>
#include <sys/mman.h>

/*********************  DEFINITIONS     ************************/

#define DEBUG_MALLOC    0       // set to one to debug malloc itself

#define DEBUG_CLIENT    0       // set to one to help debug a nasty memory smasher

#if DEBUG_MALLOC
#warning DEBUG_MALLOC ENABLED
# define INLINE
# define ALWAYSINLINE
# define CHECK_LOCKED(szone, fun)                                               \
do {                                                                            \
    if (__is_threaded && TRY_LOCK(szone->lock)) {                               \
        malloc_printf("*** lock was not set %p in %s\n", szone->lock, fun);     \
    }                                                                           \
} while (0)
#else
# define INLINE __inline__
# define ALWAYSINLINE __attribute__((always_inline))
# define CHECK_LOCKED(szone, fun)       {}
#endif

/*
 * Access to global variables is slow, so optimise our handling of vm_page_size
 * and vm_page_shift.
 */
#define _vm_page_size   vm_page_size    /* to get to the originals */
#define _vm_page_shift  vm_page_shift
#define vm_page_size    4096            /* our normal working sizes */
#define vm_page_shift   12

typedef unsigned short msize_t; // a size in multiples of SHIFT_SMALL_QUANTUM or SHIFT_TINY_QUANTUM

typedef union {
        void       *p;
        uintptr_t       u;
} ptr_union;

typedef struct {
        ptr_union previous;
        ptr_union next;
} free_list_t;

typedef struct {
    uintptr_t   address_and_num_pages;
    // this type represents both an address and a number of pages
    // the low bits are the number of pages; the high bits are the address
    // note that the exact number of bits used for depends on the page size
    // also, this cannot represent pointers larger than 1 << (vm_page_shift * 2)
} compact_range_t;

typedef unsigned char   grain_t;

#define CHECK_REGIONS                   (1 << 31)

#define MAX_RECORDER_BUFFER     256

/*********************  DEFINITIONS for tiny    ************************/

/*
 * Memory in the Tiny range is allocated from regions (heaps) pointed to by the szone's tiny_regions
 * pointer.
 *
 * Each region is laid out as a heap, followed by a header block, all within
 * a 1MB (2^20) block.  This means there are 64520 16-byte blocks and the header is
 * 16138 bytes, making the total 1048458 bytes, leaving 118 bytes unused.
 * The header block is arranged:
 *
 * 0xfc080
 *      header bits
 * 0xfe001
 *      0xffffffff pad word
 * 0xfe005
 *      in-use bits
 * 0xfff86
 *      pad word (not written)
 * 0xfff8a-0xfffff
 *      unused
 *
 * Each bitfield comprises NUM_TINY_BLOCKS bits, and refers to the corresponding TINY_QUANTUM block
 * within the heap.
 *
 * The bitfields are used to encode the state of memory within the heap.  The header bit indicates
 * that the corresponding quantum is the first quantum in a block (either in use or free).  The
 * in-use bit is set for the header if the block has been handed out (allocated).  If the header
 * bit is not set, the in-use bit is invalid.
 *
 * The szone maintains an array of 32 freelists, each of which is used to hold 
 * free objects of the corresponding quantum size.
 *
 * A free block is laid out depending on its size, in order to fit all free
 * blocks in 16 bytes, on both 32 and 64 bit platforms.  One quantum blocks do
 * not store their size in the block, instead relying on the header information
 * to determine their size.  Blocks of two or more quanta have room to store
 * their size in the block, and store it both after the 'next' pointer, and in
 * the last 2 bytes of the block.
 *
 * 1-quantum block
 * Offset (32-bit mode) (64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * end          end
 *
 * >1-quantum block
 * Offset (32-bit mode) (64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * 0x8          0x10     : size (in quantum counts)
 * end - 2      end - 2  : size (in quantum counts)
 * end          end
 *
 * All fields are pointer-sized, except for the size which is an unsigned short.
 *
 */

#define SHIFT_TINY_QUANTUM                      4       // Required for AltiVec
#define TINY_QUANTUM                            (1 << SHIFT_TINY_QUANTUM)

#define FOLLOWING_TINY_PTR(ptr,msize)           (((unsigned char *)(ptr)) + ((msize) << SHIFT_TINY_QUANTUM))

#define NUM_TINY_SLOTS                          32      // number of slots for free-lists

#define NUM_TINY_BLOCKS                         64520
#define SHIFT_TINY_CEIL_BLOCKS                  16 // ceil(log2(NUM_TINY_BLOCKS))
#define NUM_TINY_CEIL_BLOCKS                    (1 << SHIFT_TINY_CEIL_BLOCKS)
#define TINY_BLOCKS_ALIGN                       (SHIFT_TINY_CEIL_BLOCKS + SHIFT_TINY_QUANTUM)

/*
 * Enough room for the data, followed by the bit arrays (2-bits per block) plus 2 words of padding
 * as our bitmap operators overflow, plus rounding to the nearest page.
 */
#define TINY_HEADER_SIZE        ((NUM_TINY_BLOCKS >> 2) + 8)
#define TINY_REGION_SIZE        ((NUM_TINY_BLOCKS * TINY_QUANTUM + TINY_HEADER_SIZE + vm_page_size - 1) & ~ (vm_page_size - 1))

/*
 * Beginning and end pointers for a region's heap.
 */
#define TINY_REGION_ADDRESS(region)             ((void *)(region))
#define TINY_REGION_END(region)                 (TINY_REGION_ADDRESS(region) + (NUM_TINY_BLOCKS * TINY_QUANTUM))

/*
 * Locate the heap base for a pointer known to be within a tiny region.
 */
#define TINY_REGION_FOR_PTR(_p)                 ((void *)((uintptr_t)(_p) & ~((1 << TINY_BLOCKS_ALIGN) - 1)))

/*
 * Convert between byte and msize units.
 */
#define TINY_BYTES_FOR_MSIZE(_m)                ((_m) << SHIFT_TINY_QUANTUM)
#define TINY_MSIZE_FOR_BYTES(_b)                ((_b) >> SHIFT_TINY_QUANTUM)

#ifdef __LP64__
# define TINY_FREE_SIZE(ptr)                    (((msize_t *)(ptr))[8])
#else
# define TINY_FREE_SIZE(ptr)                    (((msize_t *)(ptr))[4])
#endif
#define TINY_PREVIOUS_MSIZE(ptr)                ((msize_t *)(ptr))[-1]

/*
 * Locate the block header for a pointer known to be within a tiny region.
 */
#define TINY_HEADER_START                       (NUM_TINY_BLOCKS * TINY_QUANTUM)
#define TINY_BLOCK_HEADER_FOR_PTR(_p)           ((void *)((uintptr_t)TINY_REGION_FOR_PTR(_p) + TINY_HEADER_START))

/*
 * Locate the inuse map for a given block header pointer.
 */  
#define TINY_INUSE_FOR_HEADER(_h)               ((void *)((uintptr_t)(_h) + (NUM_TINY_BLOCKS >> 3) + 4))

/*
 * Compute the bitmap index for a pointer known to be within a tiny region.
 */
#define TINY_INDEX_FOR_PTR(_p)                  (((uintptr_t)(_p) >> SHIFT_TINY_QUANTUM) & (NUM_TINY_CEIL_BLOCKS - 1))

#define TINY_CACHE      1       // This governs a last-free cache of 1 that bypasses the free-list

#if ! TINY_CACHE
#warning TINY_CACHE turned off
#endif

/*********************  DEFINITIONS for small   ************************/

/*
 * Memory in the Small range is allocated from regions (heaps) pointed to by the szone's small_regions
 * pointer.
 *
 * Each region is laid out as a heap, followed by the metadata array, all within an 8MB (2^23) block.
 * The array is arranged as an array of shorts, one for each SMALL_QUANTUM in the heap.
 * This means there are 16320 512-blocks and the array is 16320*2 bytes, which totals 8388480, leaving
 * 128 bytes unused.
 *
 * The MSB of each short is set for the first quantum in a free block.  The low 15 bits encode the
 * block size (in SMALL_QUANTUM units), or are zero if the quantum is not the first in a block.
 *
 * The szone maintains an array of 32 freelists, each of which is used to hold free objects
 * of the corresponding quantum size.
 *
 * A free block is laid out as:
 *
 * Offset (32-bit mode) (64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * 0x8          0x10     : size (in quantum counts)
 * end - 2              end - 2  : size (in quantum counts)
 * end                  end
 *
 * All fields are pointer-sized, except for the size which is an unsigned short.
 *
 */

#define SMALL_IS_FREE                           (1 << 15)

#define SHIFT_SMALL_QUANTUM                     (SHIFT_TINY_QUANTUM + 5)        // 9
#define SMALL_QUANTUM                           (1 << SHIFT_SMALL_QUANTUM) // 512 bytes

#define FOLLOWING_SMALL_PTR(ptr,msize)          (((unsigned char *)(ptr)) + ((msize) << SHIFT_SMALL_QUANTUM))

#define NUM_SMALL_SLOTS                         32      // number of slots for free-lists

/*
 * We can only represent up to 1<<15 for msize; but we choose to stay even below that to avoid the
 * convention msize=0 => msize = (1<<15)
 */
#define NUM_SMALL_BLOCKS                        16320
#define SHIFT_SMALL_CEIL_BLOCKS                 14 // ceil(log2(NUM_SMALL_BLOCKs))
#define NUM_SMALL_CEIL_BLOCKS                   (1 << SHIFT_SMALL_CEIL_BLOCKS)
#define SMALL_BLOCKS_ALIGN                      (SHIFT_SMALL_CEIL_BLOCKS + SHIFT_SMALL_QUANTUM) // 23
#define SMALL_ARRAY_SIZE                        (NUM_SMALL_BLOCKS * 2)
#define SMALL_REGION_SIZE                       ((NUM_SMALL_BLOCKS * SMALL_QUANTUM + SMALL_ARRAY_SIZE + vm_page_size - 1) & ~ (vm_page_size - 1))       // data + meta data

#define SMALL_PREVIOUS_MSIZE(ptr)               ((msize_t *)(ptr))[-1]

/*
 * Convert between byte and msize units.
 */
#define SMALL_BYTES_FOR_MSIZE(_m)               ((_m) << SHIFT_SMALL_QUANTUM)
#define SMALL_MSIZE_FOR_BYTES(_b)               ((_b) >> SHIFT_SMALL_QUANTUM)


#define SMALL_REGION_ADDRESS(region)            ((unsigned char *)region)
#define SMALL_REGION_END(region)                (SMALL_REGION_ADDRESS(region) + (NUM_SMALL_BLOCKS * SMALL_QUANTUM))

/*
 * Locate the heap base for a pointer known to be within a small region.
 */
#define SMALL_REGION_FOR_PTR(_p)                ((void *)((uintptr_t)(_p) & ~((1 << SMALL_BLOCKS_ALIGN) - 1)))

/*
 * Locate the metadata base for a pointer known to be within a small region.
 */
#define SMALL_HEADER_START                      (NUM_SMALL_BLOCKS * SMALL_QUANTUM)
#define SMALL_META_HEADER_FOR_PTR(_p)           ((msize_t *)((uintptr_t)SMALL_REGION_FOR_PTR(_p) + SMALL_HEADER_START))

/*
 * Compute the metadata index for a pointer known to be within a small region.
 */
#define SMALL_META_INDEX_FOR_PTR(_p)           (((uintptr_t)(_p) >> SHIFT_SMALL_QUANTUM) & (NUM_SMALL_CEIL_BLOCKS - 1))

/*
 * Find the metadata word for a pointer known to be within a small region.
 */
#define SMALL_METADATA_FOR_PTR(_p)              (SMALL_META_HEADER_FOR_PTR(_p) + SMALL_META_INDEX_FOR_PTR(_p))

/*
 * Determine whether a pointer known to be within a small region points to memory which is free.
 */
#define SMALL_PTR_IS_FREE(_p)                   (*SMALL_METADATA_FOR_PTR(_p) & SMALL_IS_FREE)

/*
 * Extract the msize value for a pointer known to be within a small region.
 */
#define SMALL_PTR_SIZE(_p)                      (*SMALL_METADATA_FOR_PTR(_p) & ~SMALL_IS_FREE)

#define PROTECT_SMALL                           0       // Should be 0: 1 is too slow for normal use

#define SMALL_CACHE     1
#if !SMALL_CACHE
#warning SMALL_CACHE turned off
#endif

/*********************  DEFINITIONS for large and huge  ***********************/

#define LARGE_THRESHOLD                 (15 * 1024) // at or above this use "large"

#if (LARGE_THRESHOLD > NUM_SMALL_SLOTS * SMALL_QUANTUM)
#error LARGE_THRESHOLD should always be less than NUM_SMALL_SLOTS * SMALL_QUANTUM
#endif

#define VM_COPY_THRESHOLD               (40 * 1024)
    // When all memory is touched after a copy, vm_copy() is always a lose
    // But if the memory is only read, vm_copy() wins over memmove() at 3 or 4 pages (on a G3/300MHz)
    // This must be larger than LARGE_THRESHOLD

/*
 * Given a large_entry, return the address of the allocated block.
 */
#define LARGE_ENTRY_ADDRESS(entry)                                      \
    (void *)(((entry).address_and_num_pages >> vm_page_shift) << vm_page_shift)

/*
 * Given a large entry, return the number of pages or bytes in the allocated block.
 */
#define LARGE_ENTRY_NUM_PAGES(entry)                                    \
    ((entry).address_and_num_pages & (vm_page_size - 1))
#define LARGE_ENTRY_SIZE(entry)                                         \
    (LARGE_ENTRY_NUM_PAGES(entry) << vm_page_shift)

/*
 * Compare a pointer with a large entry.
 */
#define LARGE_ENTRY_MATCHES(entry,ptr)                                  \
    ((((entry).address_and_num_pages - (uintptr_t)(ptr)) >> vm_page_shift) == 0)

#define LARGE_ENTRY_IS_EMPTY(entry)     (((entry).address_and_num_pages) == 0)

typedef compact_range_t large_entry_t;
typedef vm_range_t huge_entry_t;

/*******************************************************************************
 * Definitions for region hash
 ******************************************************************************/

typedef void * region_t;

#define INITIAL_NUM_REGIONS 63  // Must be odd to hash well

/*********************  zone itself     ************************/

typedef struct {
    malloc_zone_t       basic_zone;
    pthread_lock_t      lock;
    unsigned            debug_flags;
    void                *log_address;

    /* Regions for tiny objects */
    size_t num_tiny_regions;
    size_t num_tiny_regions_allocated;
    region_t *tiny_regions;  // hashed by location
    region_t *last_tiny_region;
    void                *last_tiny_free; // low SHIFT_TINY_QUANTUM indicate the msize
    unsigned            tiny_bitmap; // cache of the 32 free lists
    free_list_t         *tiny_free_list[NUM_TINY_SLOTS]; // 31 free lists for 1*TINY_QUANTUM to 31*TINY_QUANTUM plus 1 for larger than 32*SMALL_QUANTUM
    size_t              tiny_bytes_free_at_end; // the last free region in the last block is treated as a big block in use that is not accounted for
    unsigned            num_tiny_objects;
    size_t              num_bytes_in_tiny_objects;

    /* Regions for small objects */
    size_t num_small_regions;
    size_t num_small_regions_allocated;
    region_t *small_regions;  // hashed by location
    region_t *last_small_region;
    void                *last_small_free; // low SHIFT_SMALL_QUANTUM indicate the msize
    unsigned            small_bitmap; // cache of the free list
    free_list_t         *small_free_list[NUM_SMALL_SLOTS];
    size_t              small_bytes_free_at_end; // the last free region in the last block is treated as a big block in use that is not accounted for
    unsigned            num_small_objects;
    size_t              num_bytes_in_small_objects;

    /* large objects: vm_page_shift <= log2(size) < 2 *vm_page_shift */
    unsigned            num_large_objects_in_use;
    unsigned            num_large_entries;
    large_entry_t       *large_entries; // hashed by location; null entries don't count
    size_t              num_bytes_in_large_objects;
    
    /* huge objects: log2(size) >= 2 *vm_page_shift */
    unsigned            num_huge_entries;
    huge_entry_t        *huge_entries;
    size_t              num_bytes_in_huge_objects;

    /* Initial region list */
    region_t    initial_tiny_regions[INITIAL_NUM_REGIONS];
    region_t    initial_small_regions[INITIAL_NUM_REGIONS];
} szone_t;

#define SZONE_PAGED_SIZE        ((sizeof(szone_t) + vm_page_size - 1) & ~ (vm_page_size - 1))

#if DEBUG_MALLOC || DEBUG_CLIENT
static void             szone_sleep(void);
#endif
__private_extern__ void malloc_error_break(void);

// msg prints after fmt, ...
static void             szone_error(szone_t *szone, const char *msg, const void *ptr, const char *fmt, ...) __printflike(4, 5);

static void             protect(void *address, size_t size, unsigned protection, unsigned debug_flags);
static void             *allocate_pages(szone_t *szone, size_t size, unsigned char align, unsigned debug_flags, int vm_page_label);
static void             deallocate_pages(szone_t *szone, void *addr, size_t size, unsigned debug_flags);
static kern_return_t    _szone_default_reader(task_t task, vm_address_t address, vm_size_t size, void **ptr);

static INLINE void      free_list_checksum(szone_t *szone, free_list_t *ptr, const char *msg) ALWAYSINLINE;
static INLINE void      free_list_set_checksum(szone_t *szone, free_list_t *ptr) ALWAYSINLINE;
static INLINE uintptr_t free_list_checksum_ptr(void *p) ALWAYSINLINE;
static INLINE void * free_list_unchecksum_ptr(ptr_union ptr) ALWAYSINLINE;
static unsigned         free_list_count(const free_list_t *ptr);

static INLINE msize_t   get_tiny_meta_header(const void *ptr, boolean_t *is_free) ALWAYSINLINE;
static INLINE void      set_tiny_meta_header_in_use(const void *ptr, msize_t msize) ALWAYSINLINE;
static INLINE void      set_tiny_meta_header_middle(const void *ptr) ALWAYSINLINE;
static INLINE void      set_tiny_meta_header_free(const void *ptr, msize_t msize) ALWAYSINLINE;
static INLINE boolean_t tiny_meta_header_is_free(const void *ptr) ALWAYSINLINE;
static INLINE void      *tiny_previous_preceding_free(void *ptr, msize_t *prev_msize) ALWAYSINLINE;
static void     tiny_free_list_add_ptr(szone_t *szone, void *ptr, msize_t msize);
static void     tiny_free_list_remove_ptr(szone_t *szone, void *ptr, msize_t msize);
static INLINE region_t *tiny_region_for_ptr_no_lock(szone_t *szone, const void *ptr) ALWAYSINLINE;
static INLINE void      tiny_free_no_lock(szone_t *szone, region_t *region, void *ptr, msize_t msize) ALWAYSINLINE;
static void             *tiny_malloc_from_region_no_lock(szone_t *szone, msize_t msize);
static INLINE boolean_t try_realloc_tiny_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size) ALWAYSINLINE;
static boolean_t        tiny_check_region(szone_t *szone, region_t region);
static kern_return_t    tiny_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone, memory_reader_t reader, vm_range_recorder_t recorder);
static void     *tiny_malloc_from_free_list(szone_t *szone, msize_t msize);
static INLINE void      *tiny_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested) ALWAYSINLINE;
static INLINE void      free_tiny(szone_t *szone, void *ptr, region_t *tiny_region) ALWAYSINLINE;
static void             print_tiny_free_list(szone_t *szone);
static void             print_tiny_region(boolean_t verbose, region_t region, size_t bytes_at_end);
static boolean_t        tiny_free_list_check(szone_t *szone, grain_t slot);

static INLINE void      small_meta_header_set_is_free(msize_t *meta_headers, unsigned index, msize_t msize) ALWAYSINLINE;
static INLINE void      small_meta_header_set_in_use(msize_t *meta_headers, msize_t index, msize_t msize) ALWAYSINLINE;
static INLINE void      small_meta_header_set_middle(msize_t *meta_headers, msize_t index) ALWAYSINLINE;
static void             small_free_list_add_ptr(szone_t *szone, void *ptr, msize_t msize);
static void             small_free_list_remove_ptr(szone_t *szone, void *ptr, msize_t msize);
static INLINE region_t *small_region_for_ptr_no_lock(szone_t *szone, const void *ptr) ALWAYSINLINE;
static INLINE void      small_free_no_lock(szone_t *szone, region_t *region, void *ptr, msize_t msize) ALWAYSINLINE;
static void             *small_malloc_from_region_no_lock(szone_t *szone, msize_t msize);
static INLINE boolean_t try_realloc_small_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size) ALWAYSINLINE;
static boolean_t        szone_check_small_region(szone_t *szone, region_t region);
static kern_return_t    small_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone, memory_reader_t reader, vm_range_recorder_t recorder);
static void     *small_malloc_from_free_list(szone_t *szone, msize_t msize);
static INLINE void      *small_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested) ALWAYSINLINE;
static INLINE void      *small_malloc_cleared_no_lock(szone_t *szone, msize_t msize) ALWAYSINLINE;
static INLINE void      free_small(szone_t *szone, void *ptr, region_t *small_region) ALWAYSINLINE;
static void             print_small_free_list(szone_t *szone);
static void             print_small_region(szone_t *szone, boolean_t verbose, region_t region, size_t bytes_at_end);
static boolean_t        small_free_list_check(szone_t *szone, grain_t grain);

static region_t * hash_lookup_region_no_lock(region_t *regions, size_t num_entries, region_t r);
static void hash_region_insert_no_lock(region_t *regions, size_t num_entries, region_t r);
static region_t * hash_regions_alloc_no_lock(szone_t *szone, size_t num_entries);
static region_t * hash_regions_grow_no_lock(szone_t *szone, region_t *regions, size_t old_size, size_t *new_size);

#if DEBUG_MALLOC
static void             large_debug_print(szone_t *szone);
#endif
static large_entry_t    *large_entry_for_pointer_no_lock(szone_t *szone, const void *ptr);
static void             large_entry_insert_no_lock(szone_t *szone, large_entry_t range);
static INLINE void      large_entries_rehash_after_entry_no_lock(szone_t *szone, large_entry_t *entry) ALWAYSINLINE;
static INLINE large_entry_t *large_entries_alloc_no_lock(szone_t *szone, unsigned num) ALWAYSINLINE;
static void             large_entries_free_no_lock(szone_t *szone, large_entry_t *entries, unsigned num, vm_range_t *range_to_deallocate);
static large_entry_t *  large_entries_grow_no_lock(szone_t *szone, vm_range_t *range_to_deallocate);
static vm_range_t       large_free_no_lock(szone_t *szone, large_entry_t *entry);
static kern_return_t    large_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t large_entries_address, unsigned num_entries, memory_reader_t reader, vm_range_recorder_t recorder);
static huge_entry_t     *huge_entry_for_pointer_no_lock(szone_t *szone, const void *ptr);
static boolean_t        huge_entry_append(szone_t *szone, huge_entry_t huge);
static kern_return_t    huge_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t huge_entries_address, unsigned num_entries, memory_reader_t reader, vm_range_recorder_t recorder);
static void             *large_and_huge_malloc(szone_t *szone, size_t num_pages);
static INLINE void      free_large_or_huge(szone_t *szone, void *ptr) ALWAYSINLINE;
static INLINE int       try_realloc_large_or_huge_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size) ALWAYSINLINE;

static void             szone_free(szone_t *szone, void *ptr);
static INLINE void      *szone_malloc_should_clear(szone_t *szone, size_t size, boolean_t cleared_requested) ALWAYSINLINE;
static void             *szone_malloc(szone_t *szone, size_t size);
static void             *szone_calloc(szone_t *szone, size_t num_items, size_t size);
static void             *szone_valloc(szone_t *szone, size_t size);
static size_t           szone_size(szone_t *szone, const void *ptr);
static void             *szone_realloc(szone_t *szone, void *ptr, size_t new_size);
static unsigned         szone_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count);
static void             szone_batch_free(szone_t *szone, void **to_be_freed, unsigned count);
static void             szone_destroy(szone_t *szone);
static size_t           szone_good_size(szone_t *szone, size_t size);

static boolean_t        szone_check_all(szone_t *szone, const char *function);
static boolean_t        szone_check(szone_t *szone);
static kern_return_t    szone_ptr_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t zone_address, memory_reader_t reader, vm_range_recorder_t recorder);
static void             szone_print(szone_t *szone, boolean_t verbose);
static void             szone_log(malloc_zone_t *zone, void *log_address);
static void             szone_force_lock(szone_t *szone);
static void             szone_force_unlock(szone_t *szone);

static void             szone_statistics(szone_t *szone, malloc_statistics_t *stats);

static void             *frozen_malloc(szone_t *zone, size_t new_size);
static void             *frozen_calloc(szone_t *zone, size_t num_items, size_t size);
static void             *frozen_valloc(szone_t *zone, size_t new_size);
static void             *frozen_realloc(szone_t *zone, void *ptr, size_t new_size);
static void             frozen_free(szone_t *zone, void *ptr);
static void             frozen_destroy(szone_t *zone);

#if DEBUG_MALLOC
# define LOG(szone,ptr)                                                 \
    (szone->log_address && (((uintptr_t)szone->log_address == -1) || (szone->log_address == (void *)(ptr))))
#else
# define LOG(szone,ptr)         0
#endif

#define SZONE_LOCK(szone)                                               \
        do {                                                            \
            LOCK(szone->lock);                                          \
        } while (0)

#define SZONE_UNLOCK(szone)                                             \
        do {                                                            \
            UNLOCK(szone->lock);                                        \
        } while (0)

#define LOCK_AND_NOTE_LOCKED(szone,locked)                              \
do {                                                                    \
    CHECK(szone, __PRETTY_FUNCTION__);                                  \
    locked = 1; SZONE_LOCK(szone);                                      \
} while (0)

#if DEBUG_MALLOC || DEBUG_CLIENT
# define CHECK(szone,fun)                                               \
    if ((szone)->debug_flags & CHECK_REGIONS) szone_check_all(szone, fun)
#else
# define CHECK(szone,fun)       do {} while (0)
#endif

/*********************  VERY LOW LEVEL UTILITIES  ************************/

#if DEBUG_MALLOC || DEBUG_CLIENT
static void
szone_sleep(void)
{

    if (getenv("MallocErrorSleep")) {
        _malloc_printf(ASL_LEVEL_NOTICE, "*** sleeping to help debug\n");
        sleep(3600); // to help debug
    }
}
#endif

// msg prints after fmt, ...
static __attribute__((noinline)) void
szone_error(szone_t *szone, const char *msg, const void *ptr, const char *fmt, ...)
{
    va_list ap;
    _SIMPLE_STRING b = _simple_salloc();

    if (szone) SZONE_UNLOCK(szone);
    if (b) {
        if (fmt) {
            va_start(ap, fmt);
            _simple_vsprintf(b, fmt, ap);
            va_end(ap);
        }
        if (ptr) {
            _simple_sprintf(b, "*** error for object %p: %s\n", ptr, msg);
        } else {
            _simple_sprintf(b, "*** error: %s\n", msg);
        }
        malloc_printf("%s*** set a breakpoint in malloc_error_break to debug\n", _simple_string(b));
        _simple_sfree(b);
    } else {
        /*
         * Should only get here if vm_allocate() can't get a single page of
         * memory, implying _simple_asl_log() would also fail.  So we just
         * print to the file descriptor.
         */
        if (fmt) {
            va_start(ap, fmt);
            _malloc_vprintf(MALLOC_PRINTF_NOLOG, fmt, ap);
            va_end(ap);
        }
        if (ptr) {
            _malloc_printf(MALLOC_PRINTF_NOLOG, "*** error for object %p: %s\n", ptr, msg);
        } else {
            _malloc_printf(MALLOC_PRINTF_NOLOG, "*** error: %s\n", msg);
        }
        _malloc_printf(MALLOC_PRINTF_NOLOG, "*** set a breakpoint in malloc_error_break to debug\n");
    }
    malloc_error_break();
#if DEBUG_MALLOC
    szone_print(szone, 1);
    szone_sleep();
#endif
#if DEBUG_CLIENT
    szone_sleep();
#endif
    if (szone->debug_flags & SCALABLE_MALLOC_ABORT_ON_ERROR) abort();
}

static void
protect(void *address, size_t size, unsigned protection, unsigned debug_flags)
{
    kern_return_t       err;

    if (!(debug_flags & SCALABLE_MALLOC_DONT_PROTECT_PRELUDE)) {
        err = vm_protect(mach_task_self(), (vm_address_t)(uintptr_t)address - vm_page_size, vm_page_size, 0, protection);
        if (err) {
            malloc_printf("*** can't protect(%p) region for prelude guard page at %p\n",
              protection,address - (1 << vm_page_shift));
        }
    }
    if (!(debug_flags & SCALABLE_MALLOC_DONT_PROTECT_POSTLUDE)) {
        err = vm_protect(mach_task_self(), (vm_address_t)(uintptr_t)address + size, vm_page_size, 0, protection);
        if (err) {
            malloc_printf("*** can't protect(%p) region for postlude guard page at %p\n",
              protection, address + size);
        }
    }
}

static void *
allocate_pages(szone_t *szone, size_t size, unsigned char align, unsigned debug_flags, int vm_page_label)
{
    // align specifies a desired alignment (as a log) or 0 if no alignment requested
    void            *vm_addr;
    uintptr_t           addr, aligned_address;
    boolean_t           add_guard_pages = debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES;
    size_t              allocation_size = round_page(size);
    size_t              delta;
    
    if (align) add_guard_pages = 0; // too cumbersome to deal with that
    if (!allocation_size) allocation_size = 1 << vm_page_shift;
    if (add_guard_pages) allocation_size += 2 * (1 << vm_page_shift);
    if (align) allocation_size += (size_t)1 << align;
    vm_addr = mmap(0, allocation_size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, VM_MAKE_TAG(vm_page_label), 0);
    if ((uintptr_t)vm_addr == -1) {
        szone_error(szone, "can't allocate region", NULL, "*** mmap(size=%lld) failed (error code=%d)\n", (long long)allocation_size, errno);
            return NULL;
    }
    addr = (uintptr_t)vm_addr;
    if (align) {
        aligned_address = (addr + ((uintptr_t)1 << align) - 1) & ~ (((uintptr_t)1 << align) - 1);
        if (aligned_address != addr) {
            delta = aligned_address - addr;
            if (munmap((void *)addr, delta) == -1)
                malloc_printf("*** freeing unaligned header failed with %d\n", errno);
            addr = aligned_address;
            allocation_size -= delta;
        }
        if (allocation_size > size) {
            if (munmap((void *)(addr + size), allocation_size - size) == -1)
                malloc_printf("*** freeing unaligned footer failed with %d\n", errno);
        }
    }
    if (add_guard_pages) {
        addr += (uintptr_t)1 << vm_page_shift;
        protect((void *)addr, size, 0, debug_flags);
    }
    return (void *)addr;
}

static void
deallocate_pages(szone_t *szone, void *addr, size_t size, unsigned debug_flags)
{
    int err;
    boolean_t add_guard_pages = debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES;

    if (add_guard_pages) {
        addr -= 1 << vm_page_shift;
        size += 2 * (1 << vm_page_shift);
    }
    err = munmap(addr, size);
    if ((err == -1) && szone)
        szone_error(szone, "Can't deallocate_pages region", addr, NULL);
}

static kern_return_t
_szone_default_reader(task_t task, vm_address_t address, vm_size_t size, void **ptr)
{
    *ptr = (void *)address;
    return 0;
}

/*********************  FREE LIST UTILITIES  ************************/

// A free list entry is comprised of a pair of pointers, previous and next.
// Because the free list entries are previously freed objects, there is a
// non-zero chance that a misbehaved program will write to an allocated object
// after it has called free() on the pointer.  This write would then potentially
// corrupt the previous and next pointers, leading to a crash.  In order to
// detect this case, we take advantage of the fact that pointers are known to
// be at least 16 byte aligned, and thus have at least 4 trailing zero bits.
// When an entry is added to the free list, the previous and next pointers are
// shifted right by 2 bits, and then have the high and low 2 bits set, to act
// as guard bits.  Before accessing a free list object, we verify that these
// bits are still set, and log an error if they are not.

static INLINE void
free_list_checksum(szone_t *szone, free_list_t *ptr, const char *msg)
{
    uintptr_t ptrs = ptr->previous.u & ptr->next.u;

#ifdef __LP64__
    ptrs = (ptrs << 2) | (ptrs >> (64-2));
#else
    ptrs = (ptrs << 2) | (ptrs >> (32-2));
#endif
    
    if ((ptrs & 15) != 15)
        szone_error(szone, "incorrect checksum for freed object "
                        "- object was probably modified after being freed.", ptr, NULL);
}

static INLINE uintptr_t
free_list_checksum_ptr(void *p) 
{
    ptr_union ptr;
    ptr.p = p;
    
#ifdef __LP64__
    return (ptr.u >> 2) | 0xC000000000000003ULL;
#else
    return (ptr.u >> 2) | 0xC0000003U;
#endif
}

static INLINE void *
free_list_unchecksum_ptr(ptr_union ptr)
{
    uintptr_t u = (ptr.u >> 2) << 4;
    return (void *)u;
}

static INLINE void
free_list_set_checksum(szone_t *szone, free_list_t *ptr)
{
    ptr->previous.u = free_list_checksum_ptr(ptr->previous.p);
    ptr->next.u = free_list_checksum_ptr(ptr->next.p);
}

static unsigned
free_list_count(const free_list_t *ptr)
{
    unsigned    count = 0;

    while (ptr) {
        count++;
        ptr = free_list_unchecksum_ptr(ptr->next);
    }
    return count;
}

/* XXX inconsistent use of BITMAP32 and BITARRAY operations could be cleaned up */

#define BITMAP32_SET(bitmap,bit)        (bitmap |= 1 << (bit))
#define BITMAP32_CLR(bitmap,bit)        (bitmap &= ~ (1 << (bit)))
#define BITMAP32_BIT(bitmap,bit)        ((bitmap >> (bit)) & 1)

/* returns bit # of least-significant one bit, starting at 0 (undefined if !bitmap) */
#define BITMAP32_CTZ(bitmap) (__builtin_ctz(bitmap))

/*********************  TINY FREE LIST UTILITIES        ************************/

// We encode the meta-headers as follows:
// Each quantum has an associated set of 2 bits:
// block_header when 1 says this block is the beginning of a block
// in_use when 1 says this block is in use
// so a block in use of size 3 is 1-1 0-X 0-X
// for a free block TINY_FREE_SIZE(ptr) carries the size and the bits are 1-0 X-X X-X
// for a block middle the bits are 0-0

// Attention double evaluation for these
#define BITARRAY_SET(bits,index)        (bits[index>>3] |= (1 << (index & 7)))
#define BITARRAY_CLR(bits,index)        (bits[index>>3] &= ~(1 << (index & 7)))
#define BITARRAY_BIT(bits,index)        (((bits[index>>3]) >> (index & 7)) & 1)

// Following is for start<8 and end<=start+32
static void ALWAYSINLINE
bitarray_mclr(void *bits, unsigned start, unsigned end) {
    unsigned word = OSReadLittleInt32(bits, 0);
    unsigned mask = (0xFFFFFFFFU >> (31 - start)) >> 1;

    if (end > 31) {
        unsigned char *bytes = (unsigned char *)bits;
        bytes[4] &= ~((1 << (end - 32)) - 1);
    } else {
        mask |= (0xFFFFFFFF << end);
    }
    OSWriteLittleInt32(bits, 0, word & mask);
}

/*
 * Obtain the size of a free tiny block (in msize_t units).
 */
static msize_t
get_tiny_free_size(const void *ptr)
{
    void *next_block = (void *)((uintptr_t)ptr + TINY_QUANTUM);
    void *region_end = TINY_REGION_END(TINY_REGION_FOR_PTR(ptr));

    // check whether the next block is outside the tiny region or a block header
    // if so, then the size of this block is one, and there is no stored size.
    if (next_block < region_end)
    {
        unsigned char *next_header = TINY_BLOCK_HEADER_FOR_PTR(next_block);
        msize_t        next_index  = TINY_INDEX_FOR_PTR(next_block);
        
        if (!BITARRAY_BIT(next_header, next_index))
            return TINY_FREE_SIZE(ptr);
    }
    return 1;
}

/*
 * Get the size of the previous free block, which is stored in the last two
 * bytes of the block.  If the previous block is not free, then the result is
 * undefined.
 */
static msize_t
get_tiny_previous_free_msize(const void *ptr)
{
    // check whether the previous block is in the tiny region and a block header
    // if so, then the size of the previous block is one, and there is no stored
    // size.
    if (ptr != TINY_REGION_FOR_PTR(ptr))
    {
        void          *prev_block = (void *)((uintptr_t)ptr - TINY_QUANTUM);
        unsigned char *prev_header = TINY_BLOCK_HEADER_FOR_PTR(prev_block);
        msize_t        prev_index  = TINY_INDEX_FOR_PTR(prev_block);
        if (BITARRAY_BIT(prev_header, prev_index))
            return 1;
        return TINY_PREVIOUS_MSIZE(ptr);
    }
    // don't read possibly unmapped memory before the beginning of the region
    return 0;
}

static INLINE msize_t
get_tiny_meta_header(const void *ptr, boolean_t *is_free)
{
    // returns msize and is_free
    // may return 0 for the msize component (meaning 65536)
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;
    unsigned            byte_index;

    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    index = TINY_INDEX_FOR_PTR(ptr);
    byte_index = index >> 3;
      
    block_header += byte_index;
    index &= 7;
    *is_free = 0;
    if (!BITMAP32_BIT(*block_header, index))
        return 0;
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    if (!BITMAP32_BIT(*in_use, index)) {
        *is_free = 1;
        return get_tiny_free_size(ptr);
    }
    uint32_t    *addr = (uint32_t *)((uintptr_t)block_header & ~3);
    uint32_t    word0 = OSReadLittleInt32(addr, 0) >> index;
    uint32_t    word1 = OSReadLittleInt32(addr, 4) << (8 - index);
    uint32_t    bits = (((uintptr_t)block_header & 3) * 8);     // precision loss on LP64 OK here
    uint32_t    word = (word0 >> bits) | (word1 << (24 - bits));
    uint32_t    result = ffs(word >> 1);
    return result;
}

static INLINE void
set_tiny_meta_header_in_use(const void *ptr, msize_t msize)
{
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;
    unsigned            byte_index;
    msize_t             clr_msize;
    unsigned            end_bit;
        
    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    index = TINY_INDEX_FOR_PTR(ptr);
    byte_index = index >> 3;
    
#if DEBUG_MALLOC
    if (msize >= 32)
        malloc_printf("set_tiny_meta_header_in_use() invariant broken %p %d\n", ptr, msize);
    if ((unsigned)index + (unsigned)msize > 0x10000)
        malloc_printf("set_tiny_meta_header_in_use() invariant broken (2) %p %d\n", ptr, msize);
#endif
    block_header += byte_index;
    index &= 7;
    BITMAP32_SET(*block_header, index); 
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    BITMAP32_SET(*in_use, index); 
    index++; 
    clr_msize = msize-1;
    if (clr_msize) {
        byte_index = index >> 3;
        block_header += byte_index; in_use += byte_index;
        index &= 7;
        end_bit = index + clr_msize;
        bitarray_mclr(block_header, index, end_bit);
        bitarray_mclr(in_use, index, end_bit);
    }
    BITARRAY_SET(block_header, index+clr_msize); // we set the block_header bit for the following block to reaffirm next block is a block
#if DEBUG_MALLOC
    {
        boolean_t ff;
        msize_t mf;
        
        mf = get_tiny_meta_header(ptr, &ff);
        if (msize != mf) {
            malloc_printf("setting header for tiny in_use %p : %d\n", ptr, msize);
            malloc_printf("reading header for tiny %p : %d %d\n", ptr, mf, ff);
        }
    }
#endif
}

static INLINE void
set_tiny_meta_header_middle(const void *ptr)
{
    // indicates this block is in the middle of an in use block
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;

    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    index = TINY_INDEX_FOR_PTR(ptr);

    BITARRAY_CLR(block_header, index);
    BITARRAY_CLR(in_use, index); 
}

static INLINE void
set_tiny_meta_header_free(const void *ptr, msize_t msize)
{
    // !msize is acceptable and means 65536
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;

    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    index = TINY_INDEX_FOR_PTR(ptr);

#if DEBUG_MALLOC
    if ((unsigned)index + (unsigned)msize > 0x10000) {
        malloc_printf("setting header for tiny free %p msize too large: %d\n", ptr, msize);
    }
#endif
    BITARRAY_SET(block_header, index);
    BITARRAY_CLR(in_use, index); 
    // mark the end of this block if msize is > 1.  For msize == 0, the whole
    // region is free, so there is no following block. For msize == 1, there is
    // no space to write the size on 64 bit systems.  The size for 1 quantum
    // blocks is computed from the metadata bitmaps.
    if (msize > 1) {
        void    *follower = FOLLOWING_TINY_PTR(ptr, msize);
        TINY_PREVIOUS_MSIZE(follower) = msize;
        TINY_FREE_SIZE(ptr) = msize;
    }
    if (msize == 0) {
        TINY_FREE_SIZE(ptr) = msize;
    }
#if DEBUG_MALLOC
    boolean_t   ff;
    msize_t     mf = get_tiny_meta_header(ptr, &ff);
    if ((msize != mf) || !ff) {
        malloc_printf("setting header for tiny free %p : %u\n", ptr, msize);
        malloc_printf("reading header for tiny %p : %u %u\n", ptr, mf, ff);
    }
#endif
}

static INLINE boolean_t
tiny_meta_header_is_free(const void *ptr)
{
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;

    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    index = TINY_INDEX_FOR_PTR(ptr);
    if (!BITARRAY_BIT(block_header, index))
        return 0;
    return !BITARRAY_BIT(in_use, index);
}

static INLINE void *
tiny_previous_preceding_free(void *ptr, msize_t *prev_msize)
{
    // returns the previous block, assuming and verifying it's free
    unsigned char       *block_header;
    unsigned char       *in_use;
    msize_t             index;
    msize_t             previous_msize;
    msize_t             previous_index;
    void                *previous_ptr;

    block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
    in_use = TINY_INUSE_FOR_HEADER(block_header);
    index = TINY_INDEX_FOR_PTR(ptr);
    
    if (!index)
        return NULL;
    if ((previous_msize = get_tiny_previous_free_msize(ptr)) > index)
        return NULL;
    
    previous_index = index - previous_msize;
    previous_ptr = (void *)(TINY_REGION_FOR_PTR(ptr) + TINY_BYTES_FOR_MSIZE(previous_index));
    if (!BITARRAY_BIT(block_header, previous_index))
        return NULL;
    if (BITARRAY_BIT(in_use, previous_index))
        return NULL;
    if (get_tiny_free_size(previous_ptr) != previous_msize)
        return NULL;
    
    // conservative check did match true check
    *prev_msize = previous_msize;
    return previous_ptr;
}

/* 
 * Adds an item to the proper free list, and also marks the meta-header of the 
 * block properly.
 * Assumes szone has been locked
 */ 
static void
tiny_free_list_add_ptr(szone_t *szone, void *ptr, msize_t msize)
{
    grain_t     slot = (!msize || (msize >= NUM_TINY_SLOTS)) ? NUM_TINY_SLOTS - 1 : msize - 1;
    free_list_t *free_ptr = ptr;
    free_list_t *free_head = szone->tiny_free_list[slot];

#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
    }
    if (((uintptr_t)ptr) & (TINY_QUANTUM - 1)) {
        szone_error(szone, "tiny_free_list_add_ptr: Unaligned ptr", ptr, NULL);
    }
#endif
    set_tiny_meta_header_free(ptr, msize);
    if (free_head) {
        free_list_checksum(szone, free_head, __PRETTY_FUNCTION__);
#if DEBUG_MALLOC
        if (free_list_unchecksum_ptr(free_head->previous)) {
            szone_error(szone, "tiny_free_list_add_ptr: Internal invariant broken (free_head->previous)", ptr,
                "ptr=%p slot=%d free_head=%p previous=%p\n", ptr, slot, free_head, free_head->previous.p);
        }
        if (! tiny_meta_header_is_free(free_head)) {
            szone_error(szone, "tiny_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)", ptr,
                "ptr=%p slot=%d free_head=%p\n", ptr, slot, free_head);
        }
#endif
        free_head->previous.u = free_list_checksum_ptr(free_ptr);
    } else {
        BITMAP32_SET(szone->tiny_bitmap, slot);
    }
    free_ptr->previous.p = NULL;
    free_ptr->next.p = free_head;
    free_list_set_checksum(szone, free_ptr);
    szone->tiny_free_list[slot] = free_ptr;
}

/* 
 * Removes the item pointed to by ptr in the proper free list. 
 * Assumes szone has been locked
 */ 
static INLINE void
tiny_free_list_remove_ptr(szone_t *szone, void *ptr, msize_t msize)
{
    grain_t     slot = (!msize || (msize >= NUM_TINY_SLOTS)) ? NUM_TINY_SLOTS - 1 : msize - 1;
    free_list_t *free_ptr = ptr, *next, *previous;
    free_list_checksum(szone, free_ptr, __PRETTY_FUNCTION__);

    next = free_list_unchecksum_ptr(free_ptr->next);
    previous = free_list_unchecksum_ptr(free_ptr->previous);

#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
    }
#endif
    if (!previous) { 
    // The block to remove is the head of the free list
#if DEBUG_MALLOC
        if (szone->tiny_free_list[slot] != ptr) {
            szone_error(szone, "tiny_free_list_remove_ptr: Internal invariant broken (szone->tiny_free_list[slot])", ptr,
              "ptr=%p slot=%d msize=%d szone->tiny_free_list[slot]=%p\n",
              ptr, slot, msize, szone->tiny_free_list[slot]);
            return;
        }
#endif
        szone->tiny_free_list[slot] = next;
        if (!next) BITMAP32_CLR(szone->tiny_bitmap, slot);
    } else {
        // We know free_ptr is already checksummed, so we don't need to do it
        // again.
        previous->next = free_ptr->next;
    }
    if (next) {
        // We know free_ptr is already checksummed, so we don't need to do it
        // again.
        next->previous = free_ptr->previous;
    }
}

/*
 * tiny_region_for_ptr_no_lock - Returns the tiny region containing the pointer,
 * or NULL if not found.
 */
static INLINE region_t *
tiny_region_for_ptr_no_lock(szone_t *szone, const void *ptr)
{
  return hash_lookup_region_no_lock(szone->tiny_regions,
                                    szone->num_tiny_regions_allocated,
                                    TINY_REGION_FOR_PTR(ptr));
}

static INLINE void
tiny_free_no_lock(szone_t *szone, region_t *region, void *ptr, msize_t msize)
{
    size_t      original_size = TINY_BYTES_FOR_MSIZE(msize);
    void        *next_block = ((char *)ptr + original_size);
    msize_t     previous_msize;
    void        *previous;
    msize_t     next_msize;
    free_list_t *big_free_block;
    free_list_t *after_next_block;
    free_list_t *before_next_block;

#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in tiny_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
    }
    if (! msize) {
        szone_error(szone, "trying to free tiny block that is too small", ptr,
            "in tiny_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
    }
#endif
    // We try to coalesce this block with the preceeding one
    previous = tiny_previous_preceding_free(ptr, &previous_msize);
    if (previous) {
#if DEBUG_MALLOC
        if (LOG(szone, ptr) || LOG(szone,previous)) { 
            malloc_printf("in tiny_free_no_lock(), coalesced backwards for %p previous=%p\n", ptr, previous);
        }
#endif
        // clear the meta_header since this is no longer the start of a block
        set_tiny_meta_header_middle(ptr);
        tiny_free_list_remove_ptr(szone, previous, previous_msize);
        ptr = previous;
        msize += previous_msize;
    }
    // We try to coalesce with the next block
    if ((next_block < TINY_REGION_END(*region)) && tiny_meta_header_is_free(next_block)) {
        next_msize = get_tiny_free_size(next_block);
#if DEBUG_MALLOC
        if (LOG(szone, ptr) || LOG(szone, next_block)) {
            malloc_printf("in tiny_free_no_lock(), for ptr=%p, msize=%d coalesced forward=%p next_msize=%d\n",
              ptr, msize, next_block, next_msize);
        }
#endif
        // If we are coalescing with the next block, and the next block is in
        // the last slot of the free list, then we optimize this case here to 
        // avoid removing next_block from the slot 31 and then adding ptr back
        // to slot 31.
        if (next_msize >= NUM_TINY_SLOTS) {
            msize += next_msize;
            big_free_block = (free_list_t *)next_block;
            free_list_checksum(szone, big_free_block, __PRETTY_FUNCTION__);
            after_next_block = free_list_unchecksum_ptr(big_free_block->next);
            before_next_block = free_list_unchecksum_ptr(big_free_block->previous);
            if (!before_next_block) {
                szone->tiny_free_list[NUM_TINY_SLOTS-1] = ptr;
            } else {
                before_next_block->next.u = free_list_checksum_ptr(ptr);
            }
            if (after_next_block) {
                after_next_block->previous.u = free_list_checksum_ptr(ptr);
            }
            // we don't need to checksum these since they are already checksummed
            ((free_list_t *)ptr)->previous = big_free_block->previous;
            ((free_list_t *)ptr)->next = big_free_block->next;
            
            // clear the meta_header to enable coalescing backwards
            set_tiny_meta_header_middle(big_free_block);
            set_tiny_meta_header_free(ptr, msize);
            goto tiny_free_ending;
        }
        tiny_free_list_remove_ptr(szone, next_block, next_msize);
        set_tiny_meta_header_middle(next_block); // clear the meta_header to enable coalescing backwards
        msize += next_msize;
    }
#if !TINY_CACHE
    // The tiny cache already scribbles free blocks as they go through the
    // cache, so we do not need to do it here.
    if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && msize) {
        memset(ptr, 0x55, TINY_BYTES_FOR_MSIZE(msize));
    }
#endif
    tiny_free_list_add_ptr(szone, ptr, msize);
  tiny_free_ending:
    // When in proper debug mode we write on the memory to help debug memory smashers
    szone->num_tiny_objects--;
    szone->num_bytes_in_tiny_objects -= original_size; // we use original_size and not msize to avoid double counting the coalesced blocks
}

// Allocates from the last region or a freshly allocated region
static void *
tiny_malloc_from_region_no_lock(szone_t *szone, msize_t msize)
{
    void            *last_block, *ptr, *aligned_address;
    unsigned char   *last_header;
    msize_t         last_msize, last_index;

    // Before anything we transform any remaining tiny_bytes_free_at_end into a
    // regular free block.  We take special care here to update the bitfield
    // information, since we are bypassing the normal free codepath.  If there
    // is more than one quanta worth of memory in tiny_bytes_free_at_end, then
    // there will be two block headers:
    // 1) header for the free space at end, msize = 1
    // 2) header inserted by set_tiny_meta_header_in_use after block
    // We must clear the second one so that when the free block's size is
    // queried, we do not think the block is only 1 quantum in size because
    // of the second set header bit.
    if (szone->tiny_bytes_free_at_end) {
        last_block = TINY_REGION_END(szone->last_tiny_region) - szone->tiny_bytes_free_at_end;
        last_msize = TINY_MSIZE_FOR_BYTES(szone->tiny_bytes_free_at_end);
        last_header = TINY_BLOCK_HEADER_FOR_PTR(last_block);
        last_index  = TINY_INDEX_FOR_PTR(last_block);
        
        if (last_index != (NUM_TINY_BLOCKS - 1))
            BITARRAY_CLR(last_header, last_index + 1);
        
        tiny_free_list_add_ptr(szone, last_block, last_msize);
        szone->tiny_bytes_free_at_end = 0;
    }
    // time to create a new region
    aligned_address = allocate_pages(szone, TINY_REGION_SIZE, TINY_BLOCKS_ALIGN, 0, VM_MEMORY_MALLOC_TINY);
    if (!aligned_address) // out of memory!
        return NULL;
    // We set the padding after block_header to be all 1
    ((uint32_t *)(aligned_address + TINY_HEADER_START + (NUM_TINY_BLOCKS >> 3)))[0] = ~0;

    // Check to see if the hash ring of tiny regions needs to grow.  Try to
    // avoid the hash ring becoming too dense.
    if (szone->num_tiny_regions_allocated < (2 * szone->num_tiny_regions)) {
      region_t *new_regions;
      size_t new_size;
      new_regions = hash_regions_grow_no_lock(szone, szone->tiny_regions,
                                              szone->num_tiny_regions_allocated,
                                              &new_size);
      // Do not deallocate the current tiny_regions allocation since someone may
          // be iterating it.  Instead, just leak it.
      szone->tiny_regions = new_regions;
      szone->num_tiny_regions_allocated = new_size;
    }
    // Insert the new region into the hash ring, and update malloc statistics
    hash_region_insert_no_lock(szone->tiny_regions, 
                               szone->num_tiny_regions_allocated, 
                               aligned_address);
    szone->last_tiny_region = aligned_address;

    szone->num_tiny_regions++;
    ptr = aligned_address; 
    set_tiny_meta_header_in_use(ptr, msize);
    szone->num_tiny_objects++;
    szone->num_bytes_in_tiny_objects += TINY_BYTES_FOR_MSIZE(msize);
 
    // We put a header on the last block so that it appears in use (for coalescing, etc...)
    set_tiny_meta_header_in_use(ptr + TINY_BYTES_FOR_MSIZE(msize), 1);
    szone->tiny_bytes_free_at_end = TINY_BYTES_FOR_MSIZE(NUM_TINY_BLOCKS - msize);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in tiny_malloc_from_region_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
    }
#endif
    return ptr;
}

static INLINE boolean_t
try_realloc_tiny_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
    // returns 1 on success
    msize_t     index;
    msize_t     old_msize;
    unsigned    next_index;
    void        *next_block;
    boolean_t   is_free;
    msize_t     next_msize, coalesced_msize, leftover_msize;
    void        *leftover;

    index = TINY_INDEX_FOR_PTR(ptr);
    old_msize = TINY_MSIZE_FOR_BYTES(old_size);
    next_index = index + old_msize;
    
    if (next_index >= NUM_TINY_BLOCKS) {
        return 0;
    }
    next_block = (char *)ptr + old_size;
    SZONE_LOCK(szone);
    is_free = tiny_meta_header_is_free(next_block);
    if (!is_free) {
        SZONE_UNLOCK(szone);
        return 0; // next_block is in use;
    }
    next_msize = get_tiny_free_size(next_block);
    if (old_size + TINY_MSIZE_FOR_BYTES(next_msize) < new_size) {
        SZONE_UNLOCK(szone);
        return 0; // even with next block, not enough
    }
    tiny_free_list_remove_ptr(szone, next_block, next_msize);
    set_tiny_meta_header_middle(next_block); // clear the meta_header to enable coalescing backwards
    coalesced_msize = TINY_MSIZE_FOR_BYTES(new_size - old_size + TINY_QUANTUM - 1);
    leftover_msize = next_msize - coalesced_msize;
    if (leftover_msize) {
        leftover = next_block + TINY_BYTES_FOR_MSIZE(coalesced_msize);
        tiny_free_list_add_ptr(szone, leftover, leftover_msize);
    }
    set_tiny_meta_header_in_use(ptr, old_msize + coalesced_msize);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in try_realloc_tiny_in_place(), ptr=%p, msize=%d\n", ptr, old_msize + coalesced_msize);
    }
#endif
    szone->num_bytes_in_tiny_objects += TINY_BYTES_FOR_MSIZE(coalesced_msize);
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
    return 1;
}

static boolean_t
tiny_check_region(szone_t *szone, region_t region)
{
    uintptr_t   start, ptr, region_end;
    boolean_t   prev_free = 0;
    boolean_t   is_free;
    msize_t     msize;
    free_list_t *free_head;
    void        *follower, *previous, *next;

    /* establish region limits */
    start = (uintptr_t)TINY_REGION_ADDRESS(region);
    ptr = start;
    region_end = (uintptr_t)TINY_REGION_END(region);

    /*
     * The last region may have a trailing chunk which has not been converted into inuse/freelist
     * blocks yet.
     */
    if (region == szone->last_tiny_region)
            region_end -= szone->tiny_bytes_free_at_end;


    /*
     * Scan blocks within the region.
     */
    while (ptr < region_end) {
        /*
         * If the first block is free, and its size is 65536 (msize = 0) then the entire region is
         * free.
         */
        msize = get_tiny_meta_header((void *)ptr, &is_free);
        if (is_free && !msize && (ptr == start)) {
            return 1;
        }

        /*
         * If the block's size is 65536 (msize = 0) then since we're not the first entry the size is
         * corrupt.
         */
        if (!msize) {
            malloc_printf("*** invariant broken for tiny block %p this msize=%d - size is too small\n",
              ptr, msize);
            return 0;
        }

        if (!is_free) {
            /*
             * In use blocks cannot be more than 31 quanta large.
             */
            prev_free = 0;
            if (msize > 31 * TINY_QUANTUM) {
                malloc_printf("*** invariant broken for %p this tiny msize=%d[%p] - size is too large\n",
                  ptr, msize, msize);
                return 0;
            }
            /* move to next block */
            ptr += TINY_BYTES_FOR_MSIZE(msize);
        } else {
            /*
             * Free blocks must have been coalesced, we cannot have a free block following another
             * free block.
             */
            if (prev_free) {
                malloc_printf("*** invariant broken for free block %p this tiny msize=%d: two free blocks in a row\n",
                  ptr, msize);
                return 0;
            }
            prev_free = 1;
            /*
             * Check the integrity of this block's entry in its freelist.
             */
            free_head = (free_list_t *)ptr;
            free_list_checksum(szone, free_head, __PRETTY_FUNCTION__);
            previous = free_list_unchecksum_ptr(free_head->previous);
            next = free_list_unchecksum_ptr(free_head->next);
            if (previous && !tiny_meta_header_is_free(previous)) {
                malloc_printf("*** invariant broken for %p (previous %p is not a free pointer)\n",
                  ptr, previous);
                return 0;
            }
            if (next && !tiny_meta_header_is_free(next)) {
                malloc_printf("*** invariant broken for %p (next in free list %p is not a free pointer)\n",
                  ptr, next);
                return 0;
            }
            /*
             * Check the free block's trailing size value.
             */
            follower = FOLLOWING_TINY_PTR(ptr, msize);
            if (((uintptr_t)follower != region_end) && (get_tiny_previous_free_msize(follower) != msize)) {
                malloc_printf("*** invariant broken for tiny free %p followed by %p in region [%p-%p] "
                  "(end marker incorrect) should be %d; in fact %d\n",
                  ptr, follower, TINY_REGION_ADDRESS(region), region_end, msize, get_tiny_previous_free_msize(follower));
                return 0;
            }
            /* move to next block */
            ptr = (uintptr_t)follower;
        }
    }
    /*
     * Ensure that we scanned the entire region
     */
    if (ptr != region_end) {
        malloc_printf("*** invariant broken for region end %p - %p\n", ptr, region_end);
        return 0;
    }
    /*
     * Check the trailing block's integrity.
     */
    if (region == szone->last_tiny_region) {
        if (szone->tiny_bytes_free_at_end) {
            msize = get_tiny_meta_header((void *)ptr, &is_free);
            if (is_free || (msize != 1)) {
                malloc_printf("*** invariant broken for blocker block %p - %d %d\n", ptr, msize, is_free);
            }
        }
    }
    return 1;
}

static kern_return_t
tiny_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone, memory_reader_t reader, vm_range_recorder_t recorder)
{
  size_t num_regions = szone->num_tiny_regions_allocated;
  void *last_tiny_free = szone->last_tiny_free;
  size_t index;
  region_t      *regions;
  vm_range_t            buffer[MAX_RECORDER_BUFFER];
  unsigned              count = 0;
  kern_return_t err;
  region_t      region;
  vm_range_t            range;
  vm_range_t            admin_range;
  vm_range_t            ptr_range;
  unsigned char *mapped_region;
  unsigned char *block_header;
  unsigned char *in_use;
  unsigned              block_index;
  unsigned              block_limit;
  boolean_t             is_free;
  msize_t               msize;
  void          *mapped_ptr;
  unsigned              bit;
  vm_address_t last_tiny_free_ptr = 0;
  msize_t last_tiny_free_msize = 0;
  
  if (last_tiny_free) {
    last_tiny_free_ptr = (uintptr_t) last_tiny_free & ~(TINY_QUANTUM - 1);
    last_tiny_free_msize = (uintptr_t) last_tiny_free & (TINY_QUANTUM - 1);
  }
  
  err = reader(task, (vm_address_t)szone->tiny_regions, sizeof(region_t) * num_regions, (void **)&regions);
  if (err) return err;
  for (index = 0; index < num_regions; ++index) {
    region = regions[index];
    if (region) {
      range.address = (vm_address_t)TINY_REGION_ADDRESS(region);
      range.size = (vm_size_t)TINY_REGION_SIZE;
      if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
        admin_range.address = range.address + TINY_HEADER_START;
        admin_range.size = TINY_HEADER_SIZE;
        recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &admin_range, 1);
      }
      if (type_mask & (MALLOC_PTR_REGION_RANGE_TYPE | MALLOC_ADMIN_REGION_RANGE_TYPE)) {
        ptr_range.address = range.address;
        ptr_range.size = NUM_TINY_BLOCKS * TINY_QUANTUM;
        recorder(task, context, MALLOC_PTR_REGION_RANGE_TYPE, &ptr_range, 1);
      }
      if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
        err = reader(task, range.address, range.size, (void **)&mapped_region);
        if (err)
          return err;
        
        block_header = (unsigned char *)(mapped_region + TINY_HEADER_START);
        in_use = TINY_INUSE_FOR_HEADER(block_header);
        block_index = 0;
        block_limit = NUM_TINY_BLOCKS;
        if (region == szone->last_tiny_region)
          block_limit -= TINY_MSIZE_FOR_BYTES(szone->tiny_bytes_free_at_end);
        
        while (block_index < block_limit) {
          vm_size_t block_offset = TINY_BYTES_FOR_MSIZE(block_index);
          is_free = !BITARRAY_BIT(in_use, block_index);
          if (is_free) {
            mapped_ptr = mapped_region + block_offset;
            
            // mapped_region, the address at which 'range' in 'task' has been
            // mapped into our process, is not necessarily aligned to 
            // TINY_BLOCKS_ALIGN.
            //
            // Since the code in get_tiny_free_size() assumes the pointer came
            // from a properly aligned tiny region, and mapped_region is not
            // necessarily aligned, then do the size calculation directly.
            // If the next bit is set in the header bitmap, then the size is one
            // quantum.  Otherwise, read the size field.
            if (!BITARRAY_BIT(block_header, block_index+1))
              msize = TINY_FREE_SIZE(mapped_ptr);
            else
              msize = 1;
            
            if (!msize)
              break;
          } else if (range.address + block_offset != last_tiny_free_ptr) {
            msize = 1; 
            bit = block_index + 1;
            while (! BITARRAY_BIT(block_header, bit)) {
              bit++;
              msize ++;
            }
            buffer[count].address = range.address + block_offset;
            buffer[count].size = TINY_BYTES_FOR_MSIZE(msize);
            count++;
            if (count >= MAX_RECORDER_BUFFER) {
              recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
              count = 0;
            }
          } else {
            // Block is not free but it matches last_tiny_free_ptr so even
            // though it is not marked free in the bitmap, we treat it as if
            // it is and move on
            msize = last_tiny_free_msize;
          }
          block_index += msize;
        }
      }
    }
  }
  if (count) {
    recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
  }
  return 0;
}

static void *
tiny_malloc_from_free_list(szone_t *szone, msize_t msize)
{
    // Assumes we've locked the region
    free_list_t         *ptr;
    msize_t         this_msize;
    grain_t         slot = msize - 1;
    free_list_t         **free_list = szone->tiny_free_list;
    free_list_t         **the_slot = free_list + slot;
    free_list_t         *next;
    free_list_t         **limit;
    unsigned            bitmap;
    msize_t         leftover_msize;
    free_list_t         *leftover_ptr;

    // Assumes locked
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    
    // Look for an exact match by checking the freelist for this msize.
    // 
    ptr = *the_slot;
    if (ptr) {
        next = free_list_unchecksum_ptr(ptr->next);
        if (next) {
            next->previous = ptr->previous;
        } else {
            BITMAP32_CLR(szone->tiny_bitmap, slot);
        }
        *the_slot = next;
        this_msize = msize;
#if DEBUG_MALLOC
        if (LOG(szone, ptr)) {
            malloc_printf("in tiny_malloc_from_free_list(), exact match ptr=%p, this_msize=%d\n", ptr, this_msize);
        }
#endif
        goto return_tiny_alloc;
    }

    // Mask off the bits representing slots holding free blocks smaller than the
    // size we need.  If there are no larger free blocks, try allocating from
    // the free space at the end of the tiny region.
    bitmap = szone->tiny_bitmap & ~ ((1 << slot) - 1);
    if (!bitmap)
        goto try_tiny_malloc_from_end;
        
    slot = BITMAP32_CTZ(bitmap);
    limit = free_list + NUM_TINY_SLOTS - 1;
    free_list += slot;
    
    // Iterate over freelists looking for free blocks, starting at first list
    // which is not empty, and contains blocks which are large enough to satisfy
    // our request.
    while (free_list < limit) {
        ptr = *free_list;
        if (ptr) {
            next = free_list_unchecksum_ptr(ptr->next);
            *free_list = next;
            this_msize = get_tiny_free_size(ptr);
            if (next) {
                next->previous = ptr->previous;
            } else {
                BITMAP32_CLR(szone->tiny_bitmap, this_msize - 1);
            }
            goto add_leftover_and_proceed;
        }
        free_list++;
    }

    // We are now looking at the last slot, which contains blocks equal to, or
    // due to coalescing of free blocks, larger than 31 * tiny quantum size.
    // If the last freelist is not empty, and the head contains a block that is
    // larger than our request, then the remainder is put back on the free list.
    ptr = *limit;
    if (ptr) {
        free_list_checksum(szone, ptr, __PRETTY_FUNCTION__);
        this_msize = get_tiny_free_size(ptr);
        next = free_list_unchecksum_ptr(ptr->next);
        if (this_msize - msize >= NUM_TINY_SLOTS) {
            // the leftover will go back to the free list, so we optimize by
            // modifying the free list rather than a pop and push of the head
            leftover_msize = this_msize - msize;
            leftover_ptr = (free_list_t *)((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize));
            *limit = leftover_ptr;
            if (next) {
                next->previous.u = free_list_checksum_ptr(leftover_ptr);
            }
            leftover_ptr->previous = ptr->previous;
            leftover_ptr->next = ptr->next;
            set_tiny_meta_header_free(leftover_ptr, leftover_msize);
#if DEBUG_MALLOC
            if (LOG(szone,ptr)) {
            malloc_printf("in tiny_malloc_from_free_list(), last slot ptr=%p, msize=%d this_msize=%d\n", ptr, msize, this_msize);
            }
#endif
            this_msize = msize;
            goto return_tiny_alloc;
        }
        if (next) {
            next->previous = ptr->previous;
        }
        *limit = next;
        goto add_leftover_and_proceed;
    }

try_tiny_malloc_from_end:
    // Let's see if we can use szone->tiny_bytes_free_at_end
    if (szone->tiny_bytes_free_at_end >= TINY_BYTES_FOR_MSIZE(msize)) {
        ptr = (free_list_t *)(TINY_REGION_END(szone->last_tiny_region) - szone->tiny_bytes_free_at_end);
        szone->tiny_bytes_free_at_end -= TINY_BYTES_FOR_MSIZE(msize);
        if (szone->tiny_bytes_free_at_end) {
            // let's add an in use block after ptr to serve as boundary
            set_tiny_meta_header_in_use((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize), 1);
        }
        this_msize = msize;
#if DEBUG_MALLOC
        if (LOG(szone, ptr)) {
            malloc_printf("in tiny_malloc_from_free_list(), from end ptr=%p, msize=%d\n", ptr, msize);
        }
#endif
        goto return_tiny_alloc;
    }
    return NULL;

add_leftover_and_proceed:
    if (!this_msize || (this_msize > msize)) {
        leftover_msize = this_msize - msize;
        leftover_ptr = (free_list_t *)((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize));
#if DEBUG_MALLOC
        if (LOG(szone,ptr)) {
            malloc_printf("in tiny_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
        }
#endif
        tiny_free_list_add_ptr(szone, leftover_ptr, leftover_msize);
        this_msize = msize;
    }
    
return_tiny_alloc:
    szone->num_tiny_objects++;
    szone->num_bytes_in_tiny_objects += TINY_BYTES_FOR_MSIZE(this_msize);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in tiny_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
    }
#endif
    set_tiny_meta_header_in_use(ptr, this_msize);
    return ptr;
}

static INLINE void *
tiny_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested)
{
    boolean_t   locked = 0;
    void        *ptr;

#if DEBUG_MALLOC
    if (!msize) {
        szone_error(szone, "invariant broken (!msize) in allocation (region)", NULL, NULL);
        return(NULL);
    }
#endif
#if TINY_CACHE
    ptr = szone->last_tiny_free;
    if ((((uintptr_t)ptr) & (TINY_QUANTUM - 1)) == msize) {
        // we have a candidate - let's lock to make sure
        LOCK_AND_NOTE_LOCKED(szone, locked);
        if (ptr == szone->last_tiny_free) {
            szone->last_tiny_free = NULL;
            SZONE_UNLOCK(szone);
            CHECK(szone, __PRETTY_FUNCTION__);
            ptr = (void *)((uintptr_t)ptr & ~ (TINY_QUANTUM - 1));
            if (cleared_requested) {
                memset(ptr, 0, TINY_BYTES_FOR_MSIZE(msize));
            }
#if DEBUG_MALLOC
            if (LOG(szone,ptr)) {
                malloc_printf("in tiny_malloc_should_clear(), tiny cache ptr=%p, msize=%d\n", ptr, msize);
            }
#endif
            return ptr;
        }
    }
#endif
    // Except in rare occasions where we need to add a new region, we are going to end up locking, so we might as well lock right away to avoid doing unnecessary optimistic probes
    if (!locked) LOCK_AND_NOTE_LOCKED(szone, locked);
    ptr = tiny_malloc_from_free_list(szone, msize);
    if (ptr) {
        SZONE_UNLOCK(szone);
        CHECK(szone, __PRETTY_FUNCTION__);
        if (cleared_requested) {
            memset(ptr, 0, TINY_BYTES_FOR_MSIZE(msize));
        }
        return ptr;
    }
    ptr = tiny_malloc_from_region_no_lock(szone, msize);
    // we don't clear because this freshly allocated space is pristine
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
    return ptr;
}

static INLINE void
free_tiny(szone_t *szone, void *ptr, region_t *tiny_region)
{
    msize_t     msize;
    boolean_t   is_free;
#if TINY_CACHE
    void *ptr2;
#endif

    // ptr is known to be in tiny_region
    SZONE_LOCK(szone);
#if TINY_CACHE
    ptr2 = szone->last_tiny_free;
    /* check that we don't already have this pointer in the cache */
    if (ptr == (void *)((uintptr_t)ptr2 & ~ (TINY_QUANTUM - 1))) {
        szone_error(szone, "double free", ptr, NULL);
        return;
    }
#endif /* TINY_CACHE */
    msize = get_tiny_meta_header(ptr, &is_free);
    if (is_free) {
        szone_error(szone, "double free", ptr, NULL);
        return;
    }
#if DEBUG_MALLOC
    if (!msize) {
        malloc_printf("*** szone_free() block in use is too large: %p\n", ptr);
        return;
    }
#endif
#if TINY_CACHE
    if (msize < TINY_QUANTUM) { // to see if the bits fit in the last 4 bits
    if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && msize)
        memset(ptr, 0x55, TINY_BYTES_FOR_MSIZE(msize));
    szone->last_tiny_free = (void *)(((uintptr_t)ptr) | msize);
        if (!ptr2) {
            SZONE_UNLOCK(szone);
            CHECK(szone, __PRETTY_FUNCTION__);
            return;
        }
        msize = (uintptr_t)ptr2 & (TINY_QUANTUM - 1);
        ptr = (void *)(((uintptr_t)ptr2) & ~(TINY_QUANTUM - 1));
        tiny_region = tiny_region_for_ptr_no_lock(szone, ptr);
        if (!tiny_region) {
            szone_error(szone, "double free (tiny cache)", ptr, NULL);
        }
    }
#endif
    tiny_free_no_lock(szone, tiny_region, ptr, msize);
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
}

static void
print_tiny_free_list(szone_t *szone)
{
    grain_t     slot = 0;
    free_list_t *ptr;
    _SIMPLE_STRING b = _simple_salloc();

    if (b) {
        _simple_sappend(b, "tiny free sizes: ");
        while (slot < NUM_TINY_SLOTS) {
            ptr = szone->tiny_free_list[slot];
            if (ptr) {
                _simple_sprintf(b, "%s%y[%d]; ", (slot == NUM_TINY_SLOTS-1) ? ">=" : "", (slot+1)*TINY_QUANTUM, free_list_count(ptr));
            }
            slot++;
        }
        _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
        _simple_sfree(b);
    }
}

static void
print_tiny_region(boolean_t verbose, region_t region, size_t bytes_at_end)
{
    unsigned    counts[1024];
    unsigned    in_use = 0;
    uintptr_t   start = (uintptr_t)TINY_REGION_ADDRESS(region);
    uintptr_t   current = start;
    uintptr_t   limit =  (uintptr_t)TINY_REGION_END(region) - bytes_at_end;
    boolean_t   is_free;
    msize_t     msize;
    unsigned    ci;
    _SIMPLE_STRING b;
    
    memset(counts, 0, 1024 * sizeof(unsigned));
    while (current < limit) {
        msize = get_tiny_meta_header((void *)current, &is_free);
        if (is_free & !msize && (current == start)) {
            // first block is all free
            break;
        }
        if (!msize) {
            malloc_printf("*** error with %p: msize=%d\n", (void *)current, (unsigned)msize);
            break;
        }
        if (!is_free) {
            // block in use
            if (msize > 32)
                malloc_printf("*** error at %p msize for in_use is %d\n", (void *)current, msize);
            if (msize < 1024)
                counts[msize]++;
            in_use++;
        }
        current += TINY_BYTES_FOR_MSIZE(msize);
    }
    if ((b = _simple_salloc()) != NULL) {
        _simple_sprintf(b, "Tiny region [%p-%p, %y]\t", (void *)start, TINY_REGION_END(region), (int)TINY_REGION_SIZE);
        _simple_sprintf(b, "In_use=%d ", in_use);
        if (bytes_at_end) _simple_sprintf(b, "untouched=%ly", bytes_at_end);
        if (verbose && in_use) {
            _simple_sappend(b, "\n\tSizes in use: ");
            for (ci = 0; ci < 1024; ci++)
                if (counts[ci])
                    _simple_sprintf(b, "%d[%d]", TINY_BYTES_FOR_MSIZE(ci), counts[ci]);
        }
        _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
        _simple_sfree(b);
    }
}

static boolean_t
tiny_free_list_check(szone_t *szone, grain_t slot)
{
    unsigned    count = 0;
    free_list_t *ptr = szone->tiny_free_list[slot];
    free_list_t *previous = NULL;
    boolean_t   is_free;

    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    while (ptr) {
        free_list_checksum(szone, ptr, __PRETTY_FUNCTION__);
        is_free = tiny_meta_header_is_free(ptr);
        if (! is_free) {
            malloc_printf("*** in-use ptr in free list slot=%d count=%d ptr=%p\n", slot, count, ptr);
            return 0;
        }
        if (((uintptr_t)ptr) & (TINY_QUANTUM - 1)) {
            malloc_printf("*** unaligned ptr in free list slot=%d  count=%d ptr=%p\n", slot, count, ptr);
            return 0;
        }
        if (!tiny_region_for_ptr_no_lock(szone, ptr)) {
            malloc_printf("*** ptr not in szone slot=%d  count=%d ptr=%p\n", slot, count, ptr);
            return 0;
        }
        if (free_list_unchecksum_ptr(ptr->previous) != previous) {
            malloc_printf("*** previous incorrectly set slot=%d  count=%d ptr=%p\n", slot, count, ptr);
            return 0;
        }
        previous = ptr;
        ptr = free_list_unchecksum_ptr(ptr->next);
        count++;
    }
    return 1;
}

/*********************  SMALL FREE LIST UTILITIES       ************************/

/*
 * Mark a block as free.  Only the first quantum of a block is marked thusly,
 * the remainder are marked "middle".
 */
static INLINE void
small_meta_header_set_is_free(msize_t *meta_headers, unsigned index, msize_t msize)
{
    meta_headers[index] = msize | SMALL_IS_FREE;
}

/*
 * Mark a block as in use.  Only the first quantum of a block is marked thusly,
 * the remainder are marked "middle".
 */
static INLINE void
small_meta_header_set_in_use(msize_t *meta_headers, msize_t index, msize_t msize)
{
    meta_headers[index] = msize;
}

/*
 * Mark a quantum as being the second or later in a block.
 */
static INLINE void
small_meta_header_set_middle(msize_t *meta_headers, msize_t index)
{
    meta_headers[index] = 0;
}

// Adds an item to the proper free list
// Also marks the header of the block properly
// Assumes szone has been locked    
static void
small_free_list_add_ptr(szone_t *szone, void *ptr, msize_t msize)
{
    grain_t     slot = (msize <= NUM_SMALL_SLOTS) ? msize - 1 : NUM_SMALL_SLOTS - 1;
    free_list_t *free_ptr = ptr;
    free_list_t *free_head = szone->small_free_list[slot];
    void        *follower;

#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
    }
    if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
        szone_error(szone, "small_free_list_add_ptr: Unaligned ptr", ptr, NULL);
    }
#endif
    if (free_head) {
        free_list_checksum(szone, free_head, __PRETTY_FUNCTION__);
#if DEBUG_MALLOC
        if (free_list_unchecksum_ptr(free_head->previous)) {
            szone_error(szone, "small_free_list_add_ptr: Internal invariant broken (free_head->previous)", ptr,
                "ptr=%p slot=%d free_head=%p previous=%p\n", ptr, slot, free_head, free_head->previous.p);
        }
        if (!SMALL_PTR_IS_FREE(free_head)) {
            szone_error(szone, "small_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)", ptr,
                "ptr=%p slot=%d free_head=%p\n", ptr, slot, free_head);
        }
#endif
        free_head->previous.u = free_list_checksum_ptr(free_ptr);
    } else {
        BITMAP32_SET(szone->small_bitmap, slot);
    }
    free_ptr->previous.p = NULL;
    free_ptr->next.p = free_head;
    free_list_set_checksum(szone, free_ptr);
    szone->small_free_list[slot] = free_ptr;
    follower = ptr + SMALL_BYTES_FOR_MSIZE(msize);
    SMALL_PREVIOUS_MSIZE(follower) = msize;
}

// Removes item in the proper free list
// msize could be read, but all callers have it so we pass it in
// Assumes szone has been locked
static void
small_free_list_remove_ptr(szone_t *szone, void *ptr, msize_t msize)
{
    grain_t     slot = (msize <= NUM_SMALL_SLOTS) ? msize - 1 : NUM_SMALL_SLOTS - 1;
    free_list_t *free_ptr = ptr, *next, *previous;
    free_list_checksum(szone, free_ptr, __PRETTY_FUNCTION__);

    next = free_list_unchecksum_ptr(free_ptr->next);
    previous = free_list_unchecksum_ptr(free_ptr->previous);

#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
    }
#endif
    if (!previous) { 
    // The block to remove is the head of the free list
#if DEBUG_MALLOC
        if (szone->small_free_list[slot] != ptr) {
            szone_error(szone, "small_free_list_remove_ptr: Internal invariant broken (szone->small_free_list[grain])", ptr,
              "ptr=%p slot=%d msize=%d szone->small_free_list[slot]=%p\n",
              ptr, slot, msize, szone->small_free_list[slot]);
            return;
        }
#endif
        szone->small_free_list[slot] = next;
        if (!next) BITMAP32_CLR(szone->small_bitmap, slot);
    } else {
        // We know free_ptr is already checksummed, so we don't need to do it
        // again.
        previous->next = free_ptr->next;
    }
    if (next) {
        // We know free_ptr is already checksummed, so we don't need to do it
        // again.
        next->previous = free_ptr->previous;
    }
}

static INLINE region_t *
small_region_for_ptr_no_lock(szone_t *szone, const void *ptr)
{
  return hash_lookup_region_no_lock(szone->small_regions,
                                    szone->num_small_regions_allocated,
                                    SMALL_REGION_FOR_PTR(ptr));
}

static INLINE void
small_free_no_lock(szone_t *szone, region_t *region, void *ptr, msize_t msize)
{
    msize_t             *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
    unsigned            index = SMALL_META_INDEX_FOR_PTR(ptr);
    size_t              original_size = SMALL_BYTES_FOR_MSIZE(msize);
    unsigned char       *next_block = ((unsigned char *)ptr + original_size);
    msize_t             next_index = index + msize;
    msize_t             previous_msize, next_msize;
    void                *previous;

    // Assumes locked
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
    }
    if (! msize) {
        szone_error(szone, "trying to free small block that is too small", ptr,
            "in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
    }
#endif
    // We try to coalesce this block with the preceeding one
    if (index && (SMALL_PREVIOUS_MSIZE(ptr) <= index)) {
        previous_msize = SMALL_PREVIOUS_MSIZE(ptr);
        if (meta_headers[index - previous_msize] == (previous_msize | SMALL_IS_FREE)) {
            previous = ptr - SMALL_BYTES_FOR_MSIZE(previous_msize);
            // previous is really to be coalesced
#if DEBUG_MALLOC
            if (LOG(szone, ptr) || LOG(szone,previous)) { 
                malloc_printf("in small_free_no_lock(), coalesced backwards for %p previous=%p\n", ptr, previous);
            }
#endif
            small_free_list_remove_ptr(szone, previous, previous_msize);
            small_meta_header_set_middle(meta_headers, index);
            ptr = previous;
            msize += previous_msize;
            index -= previous_msize;
        }
    }
    // We try to coalesce with the next block
    if ((next_block < SMALL_REGION_END(*region)) && (meta_headers[next_index] & SMALL_IS_FREE)) {
        // next block is free, we coalesce
        next_msize = meta_headers[next_index] & ~ SMALL_IS_FREE;
#if DEBUG_MALLOC
        if (LOG(szone,ptr)) malloc_printf("In small_free_no_lock(), for ptr=%p, msize=%d coalesced next block=%p next_msize=%d\n", ptr, msize, next_block, next_msize);
#endif
        small_free_list_remove_ptr(szone, next_block, next_msize);
        small_meta_header_set_middle(meta_headers, next_index);
        msize += next_msize;
    }
    if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) {
        if (!msize) {
            szone_error(szone, "incorrect size information - block header was damaged", ptr, NULL);
        } else {
            memset(ptr, 0x55, SMALL_BYTES_FOR_MSIZE(msize));
        }
    }
    small_free_list_add_ptr(szone, ptr, msize);
    small_meta_header_set_is_free(meta_headers, index, msize);
    szone->num_small_objects--;
    szone->num_bytes_in_small_objects -= original_size; // we use original_size and not msize to avoid double counting the coalesced blocks
}

static void *
small_malloc_from_region_no_lock(szone_t *szone, msize_t msize)
{
    void                *last_block;
    void                *ptr;
    void                *new_address;
    msize_t             *meta_headers;
    msize_t             index ;
    msize_t             msize_left;

    // Allocates from the last region or a freshly allocated region
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    // Before anything we transform the small_bytes_free_at_end - if any - to a regular free block
    if (szone->small_bytes_free_at_end) {
      last_block = (void *)(SMALL_REGION_END(szone->last_small_region) - szone->small_bytes_free_at_end);
      small_free_list_add_ptr(szone, last_block, SMALL_MSIZE_FOR_BYTES(szone->small_bytes_free_at_end));
      *SMALL_METADATA_FOR_PTR(last_block) = SMALL_MSIZE_FOR_BYTES(szone->small_bytes_free_at_end) | SMALL_IS_FREE;
      szone->small_bytes_free_at_end = 0;
    }
    // time to create a new region
    new_address = allocate_pages(szone, SMALL_REGION_SIZE, SMALL_BLOCKS_ALIGN,
                                 0, VM_MEMORY_MALLOC_SMALL);
    if (!new_address)
      return NULL;

    ptr = new_address;
    meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
    index = 0;
    
    // Check to see if the hash ring of small regions needs to grow.  Try to
    // avoid the hash ring becoming too dense.
    if (szone->num_small_regions_allocated < (2 * szone->num_small_regions)) {
      region_t *new_regions;
      size_t new_size;
      new_regions = hash_regions_grow_no_lock(szone, szone->small_regions,
                                              szone->num_small_regions_allocated,
                                              &new_size);
      // Do not deallocate the current small_regions allocation since someone
          // may be iterating it.  Instead, just leak it.
      szone->small_regions = new_regions;
      szone->num_small_regions_allocated = new_size;
    }
    // Insert the new region into the hash ring, and update malloc statistics
    hash_region_insert_no_lock(szone->small_regions, 
                               szone->num_small_regions_allocated,
                               new_address);
    szone->last_small_region = new_address;
                               
    // we bump the number of regions AFTER we have changes the regions pointer 
    // to enable finding a small region without taking the lock
    //
    // FIXME: naive assumption assumes memory ordering coherence between this
    // and other CPUs.  This also applies to the near-identical code in
    // tiny_malloc_from_region_no_lock.
    szone->num_small_regions++;
    small_meta_header_set_in_use(meta_headers, index, msize);
    msize_left = NUM_SMALL_BLOCKS - index;
    szone->num_small_objects++;
    szone->num_bytes_in_small_objects += SMALL_BYTES_FOR_MSIZE(msize);
    // add a big free block
    index += msize; msize_left -= msize;
    meta_headers[index] = msize_left;
    szone->small_bytes_free_at_end = SMALL_BYTES_FOR_MSIZE(msize_left);
    return ptr;
}

static INLINE boolean_t
try_realloc_small_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
    // returns 1 on success
    msize_t     *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
    unsigned    index = SMALL_META_INDEX_FOR_PTR(ptr);
    msize_t     old_msize = SMALL_MSIZE_FOR_BYTES(old_size);
    msize_t     new_msize = SMALL_MSIZE_FOR_BYTES(new_size + SMALL_QUANTUM - 1);
    void        *next_block = (char *)ptr + old_size;
    unsigned    next_index = index + old_msize;
    msize_t     next_msize_and_free;
    msize_t     next_msize;
    msize_t     leftover_msize;
    void        *leftover;
    unsigned    leftover_index;

    if (next_index >= NUM_SMALL_BLOCKS) {
        return 0;
    }
#if DEBUG_MALLOC
    if ((uintptr_t)next_block & (SMALL_QUANTUM - 1)) {
        szone_error(szone, "internal invariant broken in realloc(next_block)", next_block, NULL);
    }
    if (meta_headers[index] != old_msize)
        malloc_printf("*** try_realloc_small_in_place incorrect old %d %d\n",
          meta_headers[index], old_msize);
#endif
    SZONE_LOCK(szone);
    /*
     * Look for a free block immediately afterwards.  If it's large enough, we can consume (part of)
     * it.
     */
    next_msize_and_free = meta_headers[next_index];
    next_msize = next_msize_and_free & ~ SMALL_IS_FREE;
    if (!(next_msize_and_free & SMALL_IS_FREE) || (old_msize + next_msize < new_msize)) {
        SZONE_UNLOCK(szone);
        return 0;
    }
    /*
     * The following block is big enough; pull it from its freelist and chop off enough to satisfy
     * our needs.
     */
    small_free_list_remove_ptr(szone, next_block, next_msize);
    small_meta_header_set_middle(meta_headers, next_index);
    leftover_msize = old_msize + next_msize - new_msize;
    if (leftover_msize) {
        /* there's some left, so put the remainder back */
        leftover = (unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(new_msize);
        small_free_list_add_ptr(szone, leftover, leftover_msize);
        leftover_index = index + new_msize;
        small_meta_header_set_is_free(meta_headers, leftover_index, leftover_msize);
    }
#if DEBUG_MALLOC
    if (SMALL_BYTES_FOR_MSIZE(new_msize) >= LARGE_THRESHOLD) {
        malloc_printf("*** realloc in place for %p exceeded msize=%d\n", new_msize);
    }
#endif
    small_meta_header_set_in_use(meta_headers, index, new_msize);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in szone_realloc(), ptr=%p, msize=%d\n", ptr, *SMALL_METADATA_FOR_PTR(ptr));
    }
#endif
    szone->num_bytes_in_small_objects += SMALL_BYTES_FOR_MSIZE(new_msize - old_msize);
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
    return 1;
}

static boolean_t
szone_check_small_region(szone_t *szone, region_t region)
{
    unsigned char       *ptr = SMALL_REGION_ADDRESS(region);
    msize_t             *meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
    unsigned char       *region_end = SMALL_REGION_END(region);
    msize_t             prev_free = 0;
    unsigned            index;
    msize_t             msize_and_free;
    msize_t             msize;
    free_list_t         *free_head;
    void            *previous, *next;
    msize_t             *follower;

    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    if (region == szone->last_small_region) region_end -= szone->small_bytes_free_at_end;
    while (ptr < region_end) {
        index = SMALL_META_INDEX_FOR_PTR(ptr);
        msize_and_free = meta_headers[index];
        if (!(msize_and_free & SMALL_IS_FREE)) {
            // block is in use
            msize = msize_and_free;
            if (!msize) {
                malloc_printf("*** invariant broken: null msize ptr=%p num_small_regions=%d end=%p\n",
                  ptr, szone->num_small_regions, region_end);
                return 0;
            }
            if (msize > (LARGE_THRESHOLD / SMALL_QUANTUM)) {
                malloc_printf("*** invariant broken for %p this small msize=%d - size is too large\n",
                  ptr, msize_and_free);
                return 0;
            }
            ptr += SMALL_BYTES_FOR_MSIZE(msize);
            prev_free = 0;
        } else {
            // free pointer
            msize = msize_and_free & ~ SMALL_IS_FREE;
            free_head = (free_list_t *)ptr;
            follower = (msize_t *)FOLLOWING_SMALL_PTR(ptr, msize);
            if (!msize) {
                malloc_printf("*** invariant broken for free block %p this msize=%d\n", ptr, msize);
                return 0;
            }
            if (prev_free) {
                malloc_printf("*** invariant broken for %p (2 free in a row)\n", ptr);
                return 0;
            }
            free_list_checksum(szone, free_head, __PRETTY_FUNCTION__);
            previous = free_list_unchecksum_ptr(free_head->previous);
            next = free_list_unchecksum_ptr(free_head->next);
            if (previous && !SMALL_PTR_IS_FREE(previous)) {
                malloc_printf("*** invariant broken for %p (previous %p is not a free pointer)\n",
                  ptr, free_head->previous);
                return 0;
            }
            if (next && !SMALL_PTR_IS_FREE(next)) {
                malloc_printf("*** invariant broken for %p (next is not a free pointer)\n", ptr);
                return 0;
            }
            if (SMALL_PREVIOUS_MSIZE(follower) != msize) {
                malloc_printf("*** invariant broken for small free %p followed by %p in region [%p-%p] "
                  "(end marker incorrect) should be %d; in fact %d\n",
                  ptr, follower, SMALL_REGION_ADDRESS(region), region_end, msize, SMALL_PREVIOUS_MSIZE(follower));
                return 0;
            }
            ptr = (unsigned char *)follower;
            prev_free = SMALL_IS_FREE;
        }
    }
    return 1;
}

static kern_return_t
small_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone, memory_reader_t reader, vm_range_recorder_t recorder)
{
  size_t num_regions = szone->num_small_regions_allocated;
  void *last_small_free = szone->last_small_free; 
  size_t        index;
  region_t      *regions;
  vm_range_t            buffer[MAX_RECORDER_BUFFER];
  unsigned              count = 0;
  kern_return_t err;
  region_t      region;
  vm_range_t            range;
  vm_range_t            admin_range;
  vm_range_t            ptr_range;
  unsigned char *mapped_region;
  msize_t               *block_header;
  unsigned              block_index;
  unsigned              block_limit;
  msize_t               msize_and_free;
  msize_t               msize;
  vm_address_t last_small_free_ptr = 0;
  msize_t last_small_free_msize = 0;
  
  if (last_small_free) {
    last_small_free_ptr = (uintptr_t)last_small_free & ~(SMALL_QUANTUM - 1);
    last_small_free_msize = (uintptr_t)last_small_free & (SMALL_QUANTUM - 1);
  }
  
  err = reader(task, (vm_address_t)szone->small_regions, sizeof(region_t) * num_regions, (void **)&regions);
  if (err) return err;
  for (index = 0; index < num_regions; ++index) {
    region = regions[index];
    if (region) {
      range.address = (vm_address_t)SMALL_REGION_ADDRESS(region);
      range.size = SMALL_REGION_SIZE;
      if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
        admin_range.address = range.address + SMALL_HEADER_START;
        admin_range.size = SMALL_ARRAY_SIZE;
        recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &admin_range, 1);
      }
      if (type_mask & (MALLOC_PTR_REGION_RANGE_TYPE | MALLOC_ADMIN_REGION_RANGE_TYPE)) {
        ptr_range.address = range.address;
        ptr_range.size = NUM_SMALL_BLOCKS * SMALL_QUANTUM;
        recorder(task, context, MALLOC_PTR_REGION_RANGE_TYPE, &ptr_range, 1);
      }
      if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
        err = reader(task, range.address, range.size, (void **)&mapped_region);
        if (err) return err;
        block_header = (msize_t *)(mapped_region + SMALL_HEADER_START);
        block_index = 0;
        block_limit = NUM_SMALL_BLOCKS;
        if (region == szone->last_small_region)
          block_limit -= SMALL_MSIZE_FOR_BYTES(szone->small_bytes_free_at_end);
        while (block_index < block_limit) {
          msize_and_free = block_header[block_index];
          msize = msize_and_free & ~ SMALL_IS_FREE;
          if (! (msize_and_free & SMALL_IS_FREE) &&
              range.address + SMALL_BYTES_FOR_MSIZE(block_index) != last_small_free_ptr) {
            // Block in use
            buffer[count].address = range.address + SMALL_BYTES_FOR_MSIZE(block_index);
            buffer[count].size = SMALL_BYTES_FOR_MSIZE(msize);
            count++;
            if (count >= MAX_RECORDER_BUFFER) {
              recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
              count = 0;
            }
          }
          block_index += msize;
        }
      }
    }
  }
  if (count) {
    recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
  }
  return 0;
}

static void *
small_malloc_from_free_list(szone_t *szone, msize_t msize)
{
    free_list_t         *ptr;
    msize_t         this_msize;
    grain_t         slot = (msize <= NUM_SMALL_SLOTS) ? msize - 1 : NUM_SMALL_SLOTS - 1;
    free_list_t         **free_list = szone->small_free_list;
    free_list_t     *next;
    free_list_t     **limit;
    unsigned        bitmap = szone->small_bitmap & ~ ((1 << slot) - 1);
    msize_t         leftover_msize;
    free_list_t     *leftover_ptr;
    msize_t         *meta_headers;
    unsigned        leftover_index;

    // Assumes locked
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    
    // Mask off the bits representing slots holding free blocks smaller than the
    // size we need.  If there are no larger free blocks, try allocating from
    // the free space at the end of the tiny region.
    if (!bitmap) 
        goto try_small_from_end;
        
    slot = BITMAP32_CTZ(bitmap);
    limit = free_list + NUM_SMALL_SLOTS - 1;
    free_list += slot;

    // Iterate over freelists looking for free blocks, starting at first list
    // which is not empty, and contains blocks which are large enough to satisfy
    // our request.
    while (free_list < limit) {
        ptr = *free_list;
        if (ptr) {
            next = free_list_unchecksum_ptr(ptr->next);
            *free_list = next;
            this_msize = SMALL_PTR_SIZE(ptr);
            if (next) {
                next->previous = ptr->previous;
            } else {
                BITMAP32_CLR(szone->small_bitmap, this_msize - 1);
            }
            goto add_leftover_and_proceed;
        }
        free_list++;
    }

    // We are now looking at the last slot, which contains blocks equal to, or
    // due to coalescing of free blocks, larger than 31 * small quantum size.
    // If the last freelist is not empty, and the head contains a block that is
    // larger than our request, then the remainder is put back on the free list.
    //
    // FIXME: This code doesn't have the optimization from the 'tiny' codepath 
    //        that optimizes for the this_msize >= 2 * num slots
    // FIXME: this code also seems somewhat bogus.  There's a check for
    //        this_msize >= msize, but by definition we can't ask for a small
    //        block larger than 31 small quanta, and every free block in this
    //        slot has to be at least that large.
    ptr = *limit;
    while (ptr) {
        free_list_checksum(szone, ptr, __PRETTY_FUNCTION__);
        next = free_list_unchecksum_ptr(ptr->next);
        this_msize = SMALL_PTR_SIZE(ptr);
        if (this_msize >= msize) {
            small_free_list_remove_ptr(szone, ptr, this_msize);
            goto add_leftover_and_proceed;
        }
        ptr = next;
    }
    
try_small_from_end:
    // Let's see if we can use szone->small_bytes_free_at_end
    if (szone->small_bytes_free_at_end >= SMALL_BYTES_FOR_MSIZE(msize)) {
        ptr = (free_list_t *)(SMALL_REGION_END(szone->last_small_region) - szone->small_bytes_free_at_end);
        szone->small_bytes_free_at_end -= SMALL_BYTES_FOR_MSIZE(msize);
        if (szone->small_bytes_free_at_end) {
            // let's mark this block as in use to serve as boundary
            *SMALL_METADATA_FOR_PTR((unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize)) = SMALL_MSIZE_FOR_BYTES(szone->small_bytes_free_at_end);
        }
        this_msize = msize;
        goto return_small_alloc;
    }
    return NULL;
    
add_leftover_and_proceed:
    if (this_msize > msize) {
        leftover_msize = this_msize - msize;
        leftover_ptr = (free_list_t *)((unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize));
#if DEBUG_MALLOC
        if (LOG(szone,ptr)) {
            malloc_printf("in small_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
        }
#endif
        small_free_list_add_ptr(szone, leftover_ptr, leftover_msize);
        meta_headers = SMALL_META_HEADER_FOR_PTR(leftover_ptr);
        leftover_index = SMALL_META_INDEX_FOR_PTR(leftover_ptr);
        small_meta_header_set_is_free(meta_headers, leftover_index, leftover_msize);
        this_msize = msize;
    }
    
return_small_alloc:
    szone->num_small_objects++;
    szone->num_bytes_in_small_objects += SMALL_BYTES_FOR_MSIZE(this_msize);
#if DEBUG_MALLOC
    if (LOG(szone,ptr)) {
        malloc_printf("in small_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
    }
#endif
    *SMALL_METADATA_FOR_PTR(ptr) = this_msize;
    return ptr;
}

static INLINE void *
small_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested)
{
    boolean_t   locked = 0;
#if SMALL_CACHE
    void        *ptr;
#endif
    
#if SMALL_CACHE
    ptr = (void *)szone->last_small_free;
    if ((((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) == msize) {
        // we have a candidate - let's lock to make sure
        LOCK_AND_NOTE_LOCKED(szone, locked);
        if (ptr == (void *)szone->last_small_free) {
            szone->last_small_free = NULL;
            SZONE_UNLOCK(szone);
            CHECK(szone, __PRETTY_FUNCTION__);
            ptr = (void *)((uintptr_t)ptr & ~ (SMALL_QUANTUM - 1));
            if (cleared_requested) {
                memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
            }
            return ptr;
        }
    }
#endif
    // Except in rare occasions where we need to add a new region, we are going to end up locking,
    // so we might as well lock right away to avoid doing unnecessary optimistic probes
    if (!locked) LOCK_AND_NOTE_LOCKED(szone, locked);
    ptr = small_malloc_from_free_list(szone, msize);
    if (ptr) {
        SZONE_UNLOCK(szone);
        CHECK(szone, __PRETTY_FUNCTION__);
        if (cleared_requested) {
            memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
        }
        return ptr;
    }
    ptr = small_malloc_from_region_no_lock(szone, msize);
    // we don't clear because this freshly allocated space is pristine
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
    return ptr;
}

// tries to allocate a small, cleared block
static INLINE void *
small_malloc_cleared_no_lock(szone_t *szone, msize_t msize)
{
    void        *ptr;

    // Assumes already locked
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    ptr = small_malloc_from_free_list(szone, msize);
    if (ptr) {
        memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
        return ptr;
    } else {
        ptr = small_malloc_from_region_no_lock(szone, msize);
        // we don't clear because this freshly allocated space is pristine
    }
    return ptr;
}

static INLINE void
free_small(szone_t *szone, void *ptr, region_t *small_region)
{
    msize_t             msize = SMALL_PTR_SIZE(ptr);
#if SMALL_CACHE
    void                *ptr2;
#endif
    
    // ptr is known to be in small_region
    SZONE_LOCK(szone);
#if SMALL_CACHE
    ptr2 = szone->last_small_free;
    /* check that we don't already have this pointer in the cache */
    if (ptr == (void *)((uintptr_t)ptr2 & ~ (SMALL_QUANTUM - 1))) {
        szone_error(szone, "double free", ptr, NULL);
        return;
    }
#endif
    if (SMALL_PTR_IS_FREE(ptr)) {
        szone_error(szone, "double free", ptr, NULL);
        return;
    }
#if SMALL_CACHE
    szone->last_small_free = (void *)(((uintptr_t)ptr) | msize);
    if (!ptr2) {
        SZONE_UNLOCK(szone);
        CHECK(szone, __PRETTY_FUNCTION__);
        return;
    }
    msize = (uintptr_t)ptr2 & (SMALL_QUANTUM - 1);
    ptr = (void *)(((uintptr_t)ptr2) & ~ (SMALL_QUANTUM - 1));
    small_region = small_region_for_ptr_no_lock(szone, ptr);
    if (!small_region) {
        szone_error(szone, "double free (small cache)", ptr, NULL);
        return;
    }
#endif
    small_free_no_lock(szone, small_region, ptr, msize);
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
}

static void
print_small_free_list(szone_t *szone)
{
    grain_t             grain = 0;
    free_list_t         *ptr;
    _SIMPLE_STRING      b = _simple_salloc();
    
    if (b) {
        _simple_sappend(b, "small free sizes: ");
        while (grain < NUM_SMALL_SLOTS) {
            ptr = szone->small_free_list[grain];
            if (ptr) {
                _simple_sprintf(b, "%s%y[%d]; ", (grain == NUM_SMALL_SLOTS-1) ? ">=" : "", (grain + 1) * SMALL_QUANTUM, free_list_count(ptr));
            }
            grain++;
        }
        _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
        _simple_sfree(b);
    }
}

static void
print_small_region(szone_t *szone, boolean_t verbose, region_t region, size_t bytes_at_end)
{
    unsigned            counts[1024];
    unsigned            in_use = 0;
    void                *start = SMALL_REGION_ADDRESS(region);
    void                *limit = SMALL_REGION_END(region) - bytes_at_end;
    msize_t             msize_and_free;
    msize_t             msize;
    unsigned            ci;
    _SIMPLE_STRING      b;

    memset(counts, 0, 1024 * sizeof(unsigned));
    while (start < limit) {
        msize_and_free = *SMALL_METADATA_FOR_PTR(start);
        msize = msize_and_free & ~ SMALL_IS_FREE;
        if (!(msize_and_free & SMALL_IS_FREE)) {
            // block in use
            if (msize < 1024)
                counts[msize]++;
            in_use++;
        }
        start += SMALL_BYTES_FOR_MSIZE(msize);
    }
    if ((b = _simple_salloc()) != NULL) {
        _simple_sprintf(b, "Small region [%p-%p, %y]\tIn_use=%d ",
          SMALL_REGION_ADDRESS(region), SMALL_REGION_END(region), (int)SMALL_REGION_SIZE, in_use);
        if (bytes_at_end)
            _simple_sprintf(b, "Untouched=%ly", bytes_at_end);
        if (verbose && in_use) {
            _simple_sappend(b, "\n\tSizes in use: "); 
            for (ci = 0; ci < 1024; ci++)
                if (counts[ci])
                    _simple_sprintf(b, "%d[%d] ", SMALL_BYTES_FOR_MSIZE(ci), counts[ci]);
        }
        _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
        _simple_sfree(b);
    }
}

static boolean_t
small_free_list_check(szone_t *szone, grain_t grain)
{
    unsigned    count = 0;
    free_list_t *ptr = szone->small_free_list[grain];
    free_list_t *previous = NULL;
    msize_t     msize_and_free;

    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);
    while (ptr) {
        msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
        count++;
        if (!(msize_and_free & SMALL_IS_FREE)) {
            malloc_printf("*** in-use ptr in free list grain=%d count=%d ptr=%p\n", grain, count, ptr);
            return 0;
        }
        if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
            malloc_printf("*** unaligned ptr in free list grain=%d  count=%d ptr=%p\n", grain, count, ptr);
            return 0;
        }
        if (!small_region_for_ptr_no_lock(szone, ptr)) {
            malloc_printf("*** ptr not in szone grain=%d  count=%d ptr=%p\n", grain, count, ptr);
            return 0;
        }
        free_list_checksum(szone, ptr, __PRETTY_FUNCTION__);
        if (free_list_unchecksum_ptr(ptr->previous) != previous) {
            malloc_printf("*** previous incorrectly set grain=%d  count=%d ptr=%p\n", grain, count, ptr);
            return 0;
        }
        previous = ptr;
        ptr = free_list_unchecksum_ptr(ptr->next);
    }
    return 1;
}

/*******************************************************************************
 * Region hash implementation
 *
 * This is essentially a duplicate of the existing Large allocator hash, minus
 * the ability to remove entries.  The two should be combined eventually.
 ******************************************************************************/
#pragma mark region hash

/*
 * hash_lookup_region_no_lock - Scan a hash ring looking for an entry for a 
 * given region.
 *
 * FIXME: If consecutive queries of the same region are likely, a one-entry
 * cache would likely be a significant performance win here.
 */
static region_t *
hash_lookup_region_no_lock(region_t *regions, size_t num_entries, region_t r) {
  size_t index, hash_index;
  region_t *entry;

  if (!num_entries)
    return 0;
  
  index = hash_index = ((uintptr_t)r >> 20) % num_entries;
  do {
    entry = regions + index;
    if (*entry == 0)
      return 0;
    if (*entry == r)
      return entry;
    if (++index == num_entries)
      index = 0;
  } while (index != hash_index);
  return 0;
}

/*
 * hash_region_insert_no_lock - Insert a region into the hash ring.
 */
static void
hash_region_insert_no_lock(region_t *regions, size_t num_entries, region_t r) {
  size_t index, hash_index;
  region_t *entry;
  
  index = hash_index = ((uintptr_t)r >> 20) % num_entries;
  do {
    entry = regions + index;
    if (*entry == 0) {
            *entry = r;
      return;
    }
    if (++index == num_entries)
            index = 0;
  } while (index != hash_index);
}

/*
 * hash_regions_alloc_no_lock - Allocate space for a number of entries.  This
 * must be a VM allocation as to avoid recursing between allocating a new small
 * region, and asking the small region to allocate space for the new list of
 * regions.
 */
static region_t *
hash_regions_alloc_no_lock(szone_t *szone, size_t num_entries)
{
  size_t size = num_entries * sizeof(region_t);
        return allocate_pages(szone, round_page(size), 0, 0, VM_MEMORY_MALLOC);
}

/*
 * hash_regions_grow_no_lock - Grow the hash ring, and rehash the entries.
 * Return the new region and new size to update the szone.  Do not deallocate
 * the old entries since someone may still be allocating them.
 */
static region_t *
hash_regions_grow_no_lock(szone_t *szone, region_t *regions, size_t old_size,
                          size_t *new_size)
{
  // double in size and allocate memory for the regions
  *new_size = old_size * 2 + 1;
  region_t *new_regions = hash_regions_alloc_no_lock(szone, *new_size);

  // rehash the entries into the new list
  size_t index;
  for (index = 0; index < old_size; ++index) {
    region_t r = regions[index];
    if (r != 0)
      hash_region_insert_no_lock(new_regions, *new_size, r);
  }
  return new_regions;
}

/*******************************************************************************
 * Large allocator implementation
 ******************************************************************************/
#pragma mark large allocator

#if DEBUG_MALLOC

static void
large_debug_print(szone_t *szone)
{
    unsigned            num_large_entries = szone->num_large_entries;
    unsigned            index = num_large_entries;
    large_entry_t       *range;
    _SIMPLE_STRING      b = _simple_salloc();

    if (b) {
        for (index = 0, range = szone->large_entries; index < szone->num_large_entries; index++, range++)
            if (!LARGE_ENTRY_IS_EMPTY(*range))
                _simple_sprintf(b, "%d: %p(%y);  ", index, LARGE_ENTRY_ADDRESS(*range), LARGE_ENTRY_SIZE(*range));

        _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
        _simple_sfree(b);
    }
}
#endif

/*
 * Scan the hash ring looking for an entry for the given pointer.
 */
static large_entry_t *
large_entry_for_pointer_no_lock(szone_t *szone, const void *ptr)
{
    // result only valid with lock held
    unsigned            num_large_entries = szone->num_large_entries;
    unsigned            hash_index;
    unsigned            index;
    large_entry_t       *range;

    if (!num_large_entries)
        return NULL;
    hash_index = ((uintptr_t)ptr >> vm_page_shift) % num_large_entries;
    index = hash_index;
    do {
        range = szone->large_entries + index;
        if (LARGE_ENTRY_MATCHES(*range, ptr))
            return range;
        if (LARGE_ENTRY_IS_EMPTY(*range))
            return NULL; // end of chain
        index++;
        if (index == num_large_entries)
            index = 0;
    } while (index != hash_index);
    return NULL;
}

static void
large_entry_insert_no_lock(szone_t *szone, large_entry_t range)
{
    unsigned            num_large_entries = szone->num_large_entries;
    unsigned            hash_index = (range.address_and_num_pages >> vm_page_shift) % num_large_entries;
    unsigned            index = hash_index;
    large_entry_t       *entry;

    do {
        entry = szone->large_entries + index;
        if (LARGE_ENTRY_IS_EMPTY(*entry)) {
            *entry = range;
            return; // end of chain
        }
        index++;
        if (index == num_large_entries)
            index = 0;
    } while (index != hash_index);
}

static INLINE void
large_entries_rehash_after_entry_no_lock(szone_t *szone, large_entry_t *entry)
{
    unsigned            num_large_entries = szone->num_large_entries;
    unsigned            hash_index = entry - szone->large_entries;
    unsigned            index = hash_index;
    large_entry_t       range;

    do {
        index++;
        if (index == num_large_entries)
            index = 0;
        range = szone->large_entries[index];
        if (LARGE_ENTRY_IS_EMPTY(range))
            return;
        szone->large_entries[index].address_and_num_pages = 0;
        large_entry_insert_no_lock(szone, range); // this will reinsert in the
                                                  // proper place
    } while (index != hash_index);
}

static INLINE large_entry_t *
large_entries_alloc_no_lock(szone_t *szone, unsigned num)
{
    size_t      size = num * sizeof(large_entry_t);
    boolean_t   is_vm_allocation = size >= LARGE_THRESHOLD;

    if (is_vm_allocation) {
        // Note that we allocate memory (via a system call) under a spin lock
        // That is certainly evil, however it's very rare in the lifetime of a process
        // The alternative would slow down the normal case
        return allocate_pages(szone, round_page(size), 0, 0, VM_MEMORY_MALLOC_LARGE);
    } else {
        return small_malloc_cleared_no_lock(szone, SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1));
    }
}

static void
large_entries_free_no_lock(szone_t *szone, large_entry_t *entries, unsigned num, vm_range_t *range_to_deallocate)
{
    // returns range to deallocate
    size_t              size = num * sizeof(large_entry_t);
    boolean_t           is_vm_allocation = size >= LARGE_THRESHOLD;
    region_t    *region;
    msize_t             msize_and_free;
    
    if (is_vm_allocation) {
        range_to_deallocate->address = (vm_address_t)entries;
        range_to_deallocate->size = round_page(size);
    } else {
        range_to_deallocate->size = 0;
        region = small_region_for_ptr_no_lock(szone, entries);
        msize_and_free = *SMALL_METADATA_FOR_PTR(entries);
        if (msize_and_free & SMALL_IS_FREE) {
            szone_error(szone, "object already freed being freed", entries, NULL);
            return;
        }
        small_free_no_lock(szone, region, entries, msize_and_free);
    }
}

static large_entry_t *
large_entries_grow_no_lock(szone_t *szone, vm_range_t *range_to_deallocate)
{
    // sets range_to_deallocate
    unsigned            old_num_entries = szone->num_large_entries;
    large_entry_t       *old_entries = szone->large_entries;
    unsigned            new_num_entries = (old_num_entries) ? old_num_entries * 2 + 1 : 63; // always an odd number for good hashing
    large_entry_t       *new_entries = large_entries_alloc_no_lock(szone, new_num_entries);
    unsigned            index = old_num_entries;
    large_entry_t       oldRange;

    // if the allocation of new entries failed, bail
        if (new_entries == NULL)
                return NULL;

    szone->num_large_entries = new_num_entries;
    szone->large_entries = new_entries;

    /* rehash entries into the new list */
    while (index--) {
        oldRange = old_entries[index];
        if (!LARGE_ENTRY_IS_EMPTY(oldRange)) {
            large_entry_insert_no_lock(szone, oldRange);
        }
    }
    if (old_entries) {
        large_entries_free_no_lock(szone, old_entries, old_num_entries, range_to_deallocate);
    } else {
        range_to_deallocate->size = 0;
    }
    return new_entries;
}

// frees the specific entry in the size table
// returns a range to truly deallocate
static vm_range_t
large_free_no_lock(szone_t *szone, large_entry_t *entry)
{
    vm_range_t          range;
    
    range.address = (vm_address_t)LARGE_ENTRY_ADDRESS(*entry);
    range.size = (vm_size_t)LARGE_ENTRY_SIZE(*entry);
    szone->num_large_objects_in_use--;
    szone->num_bytes_in_large_objects -= range.size;
    if (szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) {
        protect((void *)range.address, range.size, VM_PROT_READ | VM_PROT_WRITE, szone->debug_flags);
        range.address -= vm_page_size;
        range.size += 2 * vm_page_size;
    }
    entry->address_and_num_pages = 0;
    large_entries_rehash_after_entry_no_lock(szone, entry);
#if DEBUG_MALLOC
    if (large_entry_for_pointer_no_lock(szone, (void *)range.address)) {
        malloc_printf("*** freed entry %p still in use; num_large_entries=%d\n",
          range.address, szone->num_large_entries);
        large_debug_print(szone);
        szone_sleep();
    }
#endif
    return range;
}

static kern_return_t
large_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t large_entries_address, unsigned num_entries, memory_reader_t reader, vm_range_recorder_t recorder)
{
    unsigned            index = 0;
    vm_range_t          buffer[MAX_RECORDER_BUFFER];
    unsigned            count = 0;
    large_entry_t       *entries;
    kern_return_t       err;
    vm_range_t          range;
    large_entry_t       entry;

    err = reader(task, large_entries_address, sizeof(large_entry_t) * num_entries, (void **)&entries);
    if (err)
        return err;
    index = num_entries;
    if ((type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) &&
      (num_entries * sizeof(large_entry_t) >= LARGE_THRESHOLD)) {
        range.address = large_entries_address;
        range.size = round_page(num_entries * sizeof(large_entry_t));
        recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &range, 1);
    }
    if (type_mask & (MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE))
        while (index--) {
            entry = entries[index];
            if (!LARGE_ENTRY_IS_EMPTY(entry)) {
                range.address = (vm_address_t)LARGE_ENTRY_ADDRESS(entry);
                range.size = (vm_size_t)LARGE_ENTRY_SIZE(entry);
                buffer[count++] = range;
                if (count >= MAX_RECORDER_BUFFER) {
                    recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE, buffer, count);
                    count = 0;
                }
            }
        }
    if (count) {
        recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE
          | MALLOC_PTR_REGION_RANGE_TYPE, buffer, count);
    }
    return 0;
}

/*********************  HUGE ENTRY UTILITIES    ************************/

static huge_entry_t *
huge_entry_for_pointer_no_lock(szone_t *szone, const void *ptr)
{
    unsigned            index;
    huge_entry_t        *huge;

    for (index = szone->num_huge_entries, huge = szone->huge_entries;
         index > 0;
         index--, huge++) {
    
        if ((void *)huge->address == ptr)
            return huge;
    }
    return NULL;
}

static boolean_t
huge_entry_append(szone_t *szone, huge_entry_t huge)
{
    huge_entry_t        *new_huge_entries = NULL, *old_huge_entries;
    unsigned            num_huge_entries;
    
    // We do a little dance with locking because doing allocation (even in the
    // default szone) may cause something to get freed in this szone, with a
    // deadlock
    // Returns 1 on success
    SZONE_LOCK(szone);
    for (;;) {
        num_huge_entries = szone->num_huge_entries;
        SZONE_UNLOCK(szone);
        /* check for counter wrap */
        if ((num_huge_entries + 1) < num_huge_entries)
                return 0;
        /* stale allocation from last time around the loop? */
        if (new_huge_entries)
            szone_free(szone, new_huge_entries);
        new_huge_entries = szone_malloc(szone, (num_huge_entries + 1) * sizeof(huge_entry_t));
        if (new_huge_entries == NULL)
            return 0;
        SZONE_LOCK(szone);
        if (num_huge_entries == szone->num_huge_entries) {
            // No change - our malloc still applies
            old_huge_entries = szone->huge_entries;
            if (num_huge_entries) {
                memcpy(new_huge_entries, old_huge_entries, num_huge_entries * sizeof(huge_entry_t));
            }
            new_huge_entries[szone->num_huge_entries++] = huge;
            szone->huge_entries = new_huge_entries;
            SZONE_UNLOCK(szone);
            szone_free(szone, old_huge_entries);
            return 1;
        }
        // try again!
    }
}

static kern_return_t
huge_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t huge_entries_address, unsigned num_entries, memory_reader_t reader, vm_range_recorder_t recorder)
{
    huge_entry_t        *entries;
    kern_return_t       err;
    
    err = reader(task, huge_entries_address, sizeof(huge_entry_t) * num_entries, (void **)&entries);
    if (err)
        return err;
    if (num_entries)
        recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE, entries, num_entries);

    return 0;
}

static void *
large_and_huge_malloc(szone_t *szone, size_t num_pages)
{
    void                *addr;
    vm_range_t          range_to_deallocate;
    huge_entry_t        huge_entry;
    size_t              size;
    large_entry_t       large_entry;
    
    if (!num_pages)
            num_pages = 1; // minimal allocation size for this szone
    size = (size_t)num_pages << vm_page_shift;
    range_to_deallocate.size = 0;
    if (num_pages >= (1 << vm_page_shift)) {
        addr = allocate_pages(szone, size, 0, szone->debug_flags, VM_MEMORY_MALLOC_HUGE);
        if (addr == NULL)
            return NULL;
        huge_entry.size = size;
        huge_entry.address = (vm_address_t)addr;
        if (!huge_entry_append(szone, huge_entry))
            return NULL;        // we are leaking the allocation here
        SZONE_LOCK(szone);
        szone->num_bytes_in_huge_objects += size;
    } else {

        addr = allocate_pages(szone, size, 0, szone->debug_flags, VM_MEMORY_MALLOC_LARGE);
#if DEBUG_MALLOC
        if (LOG(szone, addr))
            malloc_printf("in szone_malloc true large allocation at %p for %ly\n", (void *)addr, size);
#endif
        SZONE_LOCK(szone);
        if (addr == NULL) {
            SZONE_UNLOCK(szone);
            return NULL;
        }
#if DEBUG_MALLOC
        if (large_entry_for_pointer_no_lock(szone, addr)) {
            malloc_printf("freshly allocated is already in use: %p\n", addr);
            large_debug_print(szone);
            szone_sleep();
        }
#endif
        if ((szone->num_large_objects_in_use + 1) * 4 > szone->num_large_entries) {
            // density of hash table too high; grow table
            // we do that under lock to avoid a race
            large_entry_t *entries = large_entries_grow_no_lock(szone, &range_to_deallocate);
            if (entries == NULL) {
                SZONE_UNLOCK(szone);
                return NULL;
            }
        }
        large_entry.address_and_num_pages = (uintptr_t)addr | num_pages;
#if DEBUG_MALLOC
        if (large_entry_for_pointer_no_lock(szone, addr)) {
            malloc_printf("entry about to be added already in use: %p\n", addr);
            large_debug_print(szone);
            szone_sleep();
        }
#endif
        large_entry_insert_no_lock(szone, large_entry);
#if DEBUG_MALLOC
        if (!large_entry_for_pointer_no_lock(szone, (void *)addr)) {
            malloc_printf("can't find entry just added\n");
            large_debug_print(szone);
            szone_sleep();
        }
#endif
        szone->num_large_objects_in_use ++;
        szone->num_bytes_in_large_objects += size;
    }
    SZONE_UNLOCK(szone);
    if (range_to_deallocate.size) {
        deallocate_pages(szone, (void *)range_to_deallocate.address, range_to_deallocate.size, 0); // we deallocate outside the lock
    }
    return (void *)addr;
}

static INLINE void
free_large_or_huge(szone_t *szone, void *ptr)
{
    // We have established ptr is page-aligned and not tiny nor small
    large_entry_t       *entry;
    vm_range_t          vm_range_to_deallocate;
    huge_entry_t        *huge;
    
    SZONE_LOCK(szone);
    entry = large_entry_for_pointer_no_lock(szone, ptr);
    if (entry) {
        vm_range_to_deallocate = large_free_no_lock(szone, entry);
#if DEBUG_MALLOC
        if (large_entry_for_pointer_no_lock(szone, ptr)) {
            malloc_printf("*** just after freeing %p still in use num_large_entries=%d\n", ptr, szone->num_large_entries);
            large_debug_print(szone);
            szone_sleep();
        }
#endif
    } else if ((huge = huge_entry_for_pointer_no_lock(szone, ptr))) {
        vm_range_to_deallocate = *huge;
        *huge = szone->huge_entries[--szone->num_huge_entries]; // last entry fills that spot
        szone->num_bytes_in_huge_objects -= (size_t)vm_range_to_deallocate.size;
    } else {
#if DEBUG_MALLOC
        large_debug_print(szone);
#endif
        szone_error(szone, "pointer being freed was not allocated", ptr, NULL);
        return;
    }
    SZONE_UNLOCK(szone); // we release the lock asap
    CHECK(szone, __PRETTY_FUNCTION__);
    // we deallocate_pages, including guard pages
    if (vm_range_to_deallocate.address) {
#if DEBUG_MALLOC
        if (large_entry_for_pointer_no_lock(szone, (void *)vm_range_to_deallocate.address)) {
            malloc_printf("*** invariant broken: %p still in use num_large_entries=%d\n", vm_range_to_deallocate.address, szone->num_large_entries);
            large_debug_print(szone);
            szone_sleep();
        }
#endif
        deallocate_pages(szone, (void *)vm_range_to_deallocate.address, (size_t)vm_range_to_deallocate.size, 0);
    }
}

static INLINE int
try_realloc_large_or_huge_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
    vm_address_t        addr = (vm_address_t)ptr + old_size;
    large_entry_t       *large_entry, saved_entry;
    huge_entry_t        *huge_entry, huge;
    kern_return_t       err;

#if DEBUG_MALLOC
    if (old_size != ((old_size >> vm_page_shift) << vm_page_shift)) {
        malloc_printf("*** old_size is %d\n", old_size);
    }
#endif
    SZONE_LOCK(szone);
    large_entry = large_entry_for_pointer_no_lock(szone, (void *)addr);
    SZONE_UNLOCK(szone);
    if (large_entry) {
        return 0; // large pointer already exists in table - extension is not going to work
    }
    new_size = round_page(new_size);
    /*
     * Ask for allocation at a specific address, and mark as realloc
     * to request coalescing with previous realloc'ed extensions.
     */
    err = vm_allocate(mach_task_self(), &addr, new_size - old_size, VM_MAKE_TAG(VM_MEMORY_REALLOC));
    if (err != KERN_SUCCESS) {
        return 0;
    }
    SZONE_LOCK(szone);
    /*
     * If the new size is still under the large/huge threshold, we can just
     * extend the existing large block.
     *
     * Note: this logic is predicated on the understanding that an allocated
     * block can never really shrink, so that the new size will always be 
     * larger than the old size.
     *
     * Note: the use of 1 << vm_page_shift here has to do with the subdivision
     * of the bits in the large_entry_t, and not the size of a page (directly).
     */
    if ((new_size >> vm_page_shift) < (1 << vm_page_shift)) {
        /* extend existing large entry */
        large_entry = large_entry_for_pointer_no_lock(szone, ptr);
        if (!large_entry) {
            szone_error(szone, "large entry reallocated is not properly in table", ptr, NULL);
            /* XXX will cause fault on next reference to entry */
        }
        large_entry->address_and_num_pages = (uintptr_t)ptr | (new_size >> vm_page_shift);
        szone->num_bytes_in_large_objects += new_size - old_size;
    } else if ((old_size >> vm_page_shift) >= (1 << vm_page_shift)) {
        /* extend existing huge entry */
        huge_entry = huge_entry_for_pointer_no_lock(szone, ptr);
        if (!huge_entry) {
            szone_error(szone, "huge entry reallocated is not properly in table", ptr, NULL);
            /* XXX will cause fault on next reference to huge_entry */
        }
        huge_entry->size = new_size;
        szone->num_bytes_in_huge_objects += new_size - old_size;
    } else {
        /* need to convert large entry to huge entry */

        /* release large entry, note we still have the VM allocation */
        large_entry = large_entry_for_pointer_no_lock(szone, ptr);
        saved_entry = *large_entry; // in case we need to put it back
        large_free_no_lock(szone, large_entry);

        /* and get a huge entry */
        huge.address = (vm_address_t)ptr;
        huge.size = new_size;   /* fix up size */
        SZONE_UNLOCK(szone);
        if (huge_entry_append(szone, huge)) {
            szone->num_bytes_in_huge_objects += new_size;
            return 1; // success!
        }
        SZONE_LOCK(szone);
        // we leak memory (the extra space appended) but data structures are correct
        large_entry_insert_no_lock(szone, saved_entry); // this will reinsert the large entry
    }
    SZONE_UNLOCK(szone); // we release the lock asap
    return 1;
}

/*********************  Zone call backs ************************/

static void
szone_free(szone_t *szone, void *ptr)
{
    region_t    *tiny_region;
    region_t    *small_region;

#if DEBUG_MALLOC
    if (LOG(szone, ptr))
        malloc_printf("in szone_free with %p\n", ptr);
#endif
    if (!ptr)
        return;
    /*
     * Try to free to a tiny region.
     */
    if ((uintptr_t)ptr & (TINY_QUANTUM - 1)) {
        szone_error(szone, "Non-aligned pointer being freed", ptr, NULL);
        return;
    }
    if ((tiny_region = tiny_region_for_ptr_no_lock(szone, ptr)) != NULL) {
        if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS) {
            szone_error(szone, "Pointer to metadata being freed", ptr, NULL);
            return;
        }
        free_tiny(szone, ptr, tiny_region);
        return;
    }

    /*
     * Try to free to a small region.
     */
    if ((uintptr_t)ptr & (SMALL_QUANTUM - 1)) {
        szone_error(szone, "Non-aligned pointer being freed (2)", ptr, NULL);
        return;
    }
    if ((small_region = small_region_for_ptr_no_lock(szone, ptr)) != NULL) {
        if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS) {
            szone_error(szone, "Pointer to metadata being freed (2)", ptr, NULL);
            return;
        }
        free_small(szone, ptr, small_region);
        return;
    }

    /* check that it's a legal large/huge allocation */
    if ((uintptr_t)ptr & (vm_page_size - 1)) {
        szone_error(szone, "non-page-aligned, non-allocated pointer being freed", ptr, NULL);
        return;
    }
    free_large_or_huge(szone, ptr);
}

static INLINE void *
szone_malloc_should_clear(szone_t *szone, size_t size, boolean_t cleared_requested)
{
    void        *ptr;
    msize_t     msize;

    if (size <= 31*TINY_QUANTUM) {
        // think tiny
        msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
        if (!msize)
            msize = 1;
        ptr = tiny_malloc_should_clear(szone, msize, cleared_requested);
    } else if (!((szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) && PROTECT_SMALL) && (size < LARGE_THRESHOLD)) {
        // think small
        msize = SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1);
        if (! msize) msize = 1;
        ptr = small_malloc_should_clear(szone, msize, cleared_requested);
    } else {
        // large or huge
        size_t num_pages = round_page(size) >> vm_page_shift;
        if (num_pages == 0)     /* Overflowed */
                ptr = 0;
        else
        ptr = large_and_huge_malloc(szone, num_pages);
    }
#if DEBUG_MALLOC
    if (LOG(szone, ptr))
        malloc_printf("szone_malloc returned %p\n", ptr);
#endif
    /*
     * If requested, scribble on allocated memory.
     */
    if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && ptr && !cleared_requested && size)
        memset(ptr, 0xaa, size);

    return ptr;
}

static void *
szone_malloc(szone_t *szone, size_t size) {
    return szone_malloc_should_clear(szone, size, 0);
}

static void *
szone_calloc(szone_t *szone, size_t num_items, size_t size)
{
    size_t total_bytes = num_items * size;
    if ((num_items > 1) && (size != 0) && ((total_bytes / size) != num_items))
        return NULL;
    return szone_malloc_should_clear(szone, total_bytes, 1);
}

static void *
szone_valloc(szone_t *szone, size_t size)
{
    void        *ptr;
    size_t num_pages;
    
    num_pages = round_page(size) >> vm_page_shift;
    ptr = large_and_huge_malloc(szone, num_pages);
#if DEBUG_MALLOC
    if (LOG(szone, ptr))
        malloc_printf("szone_valloc returned %p\n", ptr);
#endif
    return ptr;
}

static size_t
szone_size(szone_t *szone, const void *ptr)
{
    size_t              size = 0;
    boolean_t           is_free;
    msize_t             msize, msize_and_free;
    large_entry_t       *entry;
    huge_entry_t        *huge;
    
    if (!ptr)
        return 0;
#if DEBUG_MALLOC
    if (LOG(szone, ptr)) {
        malloc_printf("in szone_size for %p (szone=%p)\n", ptr, szone);
    }
#endif

    /*
     * Look for it in a tiny region.
     */
    if ((uintptr_t)ptr & (TINY_QUANTUM - 1))
        return 0;
    if (tiny_region_for_ptr_no_lock(szone, ptr)) {
        if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS)
            return 0;
        msize = get_tiny_meta_header(ptr, &is_free);
        return (is_free) ? 0 : TINY_BYTES_FOR_MSIZE(msize);
    }
    
    /*
     * Look for it in a small region.
     */
    if ((uintptr_t)ptr & (SMALL_QUANTUM - 1))
        return 0;
    if (small_region_for_ptr_no_lock(szone, ptr)) {
        if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS)
            return 0;
        msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
        return (msize_and_free & SMALL_IS_FREE) ? 0 : SMALL_BYTES_FOR_MSIZE(msize_and_free);
    }

    /*
     * If not page-aligned, it cannot have come from a large or huge allocation.
     */
    if ((uintptr_t)ptr & (vm_page_size - 1))
        return(0);

    /*
     * Look for it in a large or huge entry.
     */
    SZONE_LOCK(szone);
    entry = large_entry_for_pointer_no_lock(szone, ptr);
    if (entry) {
        size = LARGE_ENTRY_SIZE(*entry);
    } else if ((huge = huge_entry_for_pointer_no_lock(szone, ptr))) {
        size = huge->size;
    }
    SZONE_UNLOCK(szone); 
#if DEBUG_MALLOC
    if (LOG(szone, ptr)) {
        malloc_printf("szone_size for %p returned %d\n", ptr, (unsigned)size);
    }
#endif
    return size;
}

static void *
szone_realloc(szone_t *szone, void *ptr, size_t new_size)
{
    size_t              old_size;
    void                *new_ptr;
    
#if DEBUG_MALLOC
    if (LOG(szone, ptr)) {
        malloc_printf("in szone_realloc for %p, %d\n", ptr, (unsigned)new_size);
    }
#endif
    if (!ptr) {
        ptr = szone_malloc(szone, new_size);
        return ptr;
    }
    old_size = szone_size(szone, ptr);
    if (!old_size) {
        szone_error(szone, "pointer being reallocated was not allocated", ptr, NULL);
        return NULL;
    }
    /* we never shrink an allocation */
    if (old_size >= new_size)
        return ptr;

    /*
     * If the old and new sizes both suit the tiny allocator, try to reallocate in-place.
     */
    if ((new_size + TINY_QUANTUM - 1) <= 31 * TINY_QUANTUM) {
        if (try_realloc_tiny_in_place(szone, ptr, old_size, new_size)) {
            return ptr;
        }

        /*
         * If the old and new sizes both suit the small allocator, and we're not protecting the
         * small allocations, try to reallocate in-place.
         */
    } else if (!((szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) && PROTECT_SMALL) &&
      ((new_size + SMALL_QUANTUM - 1) < LARGE_THRESHOLD) &&
      (old_size > 31 * TINY_QUANTUM)) {
        if (try_realloc_small_in_place(szone, ptr, old_size, new_size)) {
            return ptr;
        }

        /*
         * If the allocation's a large or huge allocation, try to reallocate in-place there.
         */
    } else if (!((szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) && PROTECT_SMALL) && (old_size > LARGE_THRESHOLD)) {
        if (try_realloc_large_or_huge_in_place(szone, ptr, old_size, new_size)) {
            return ptr;
        }
    }

    /*
     * Can't reallocate in place for whatever reason; allocate a new buffer and copy.
     */
    new_ptr = szone_malloc(szone, new_size);
    if (new_ptr == NULL)
        return NULL;

    /*
     * If the allocation's large enough, try to copy using VM.  If that fails, or
     * if it's too small, just copy by hand.
     */
    if ((old_size < VM_COPY_THRESHOLD) ||
      vm_copy(mach_task_self(), (vm_address_t)ptr, old_size, (vm_address_t)new_ptr))
        memcpy(new_ptr, ptr, old_size);
    szone_free(szone, ptr);
    
#if DEBUG_MALLOC
    if (LOG(szone, ptr)) {
        malloc_printf("szone_realloc returned %p for %d\n", new_ptr, (unsigned)new_size);
    }
#endif
    return new_ptr;
}

// given a size, returns the number of pointers allocated capable of holding
// that size, up to the limit specified by the 'count' argument.  These pointers
// are stored in the 'results' array, which must be allocated by the caller.
// may return zero, since this function is only a best attempt at allocating
// the pointers.  clients should be prepared to call malloc for any additional
// blocks they need.
static unsigned
szone_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count)
{
    msize_t     msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
    unsigned    found = 0;

    // only bother implementing this for tiny
    if (size > 31*TINY_QUANTUM)
        return 0;
    // make sure to return objects at least one quantum in size
    if (!msize)
        msize = 1;

    CHECK(szone, __PRETTY_FUNCTION__);

        // We must lock the zone now, since tiny_malloc_from_free_list assumes that 
        // the caller has done so.
    SZONE_LOCK(szone);

        // with the zone locked, allocate objects from the free list until all
        // sufficiently large objects have been exhausted, or we have met our quota
        // of objects to allocate.
        while (found < count) {
        void *ptr = tiny_malloc_from_free_list(szone, msize);
        if (!ptr)
            break;

        *results++ = ptr;
        found++;
    }
    SZONE_UNLOCK(szone);
    return found;
}

static void
szone_batch_free(szone_t *szone, void **to_be_freed, unsigned count)
{
    unsigned            cc = 0;
    void                *ptr;
    region_t    *tiny_region;
    boolean_t           is_free;
    msize_t             msize;

    // frees all the pointers in to_be_freed
    // note that to_be_freed may be overwritten during the process
    if (!count)
        return;
    CHECK(szone, __PRETTY_FUNCTION__);
    SZONE_LOCK(szone);
    while (cc < count) {
        ptr = to_be_freed[cc];
        if (ptr) {
            /* XXX this really slows us down */
            tiny_region = tiny_region_for_ptr_no_lock(szone, ptr);
            if (tiny_region) {
                // this is a tiny pointer
                if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS)
                    break; // pointer to metadata; let the standard free deal with it
                msize = get_tiny_meta_header(ptr, &is_free);
                if (is_free)
                    break; // a double free; let the standard free deal with it
                tiny_free_no_lock(szone, tiny_region, ptr, msize);
                to_be_freed[cc] = NULL;
            }
        }
        cc++;
    }
    SZONE_UNLOCK(szone);
    CHECK(szone, __PRETTY_FUNCTION__);
    while (count--) {
        ptr = to_be_freed[count];
        if (ptr)
            szone_free(szone, ptr);
    }
}

static void
szone_destroy(szone_t *szone)
{
    size_t              index;
    large_entry_t       *large;
    vm_range_t          range_to_deallocate;
    huge_entry_t        *huge;

    /* destroy large entries */
    index = szone->num_large_entries;
    while (index--) {
        large = szone->large_entries + index;
        if (!LARGE_ENTRY_IS_EMPTY(*large)) {
            // we deallocate_pages, including guard pages
            deallocate_pages(szone, (void *)LARGE_ENTRY_ADDRESS(*large), LARGE_ENTRY_SIZE(*large), szone->debug_flags);
        }
    }
    if (szone->num_large_entries * sizeof(large_entry_t) >= LARGE_THRESHOLD) {
        // we do not free in the small chunk case
        large_entries_free_no_lock(szone, szone->large_entries, szone->num_large_entries, &range_to_deallocate);
        if (range_to_deallocate.size)
            deallocate_pages(szone, (void *)range_to_deallocate.address, (size_t)range_to_deallocate.size, 0);
    }

    /* destroy huge entries */
    index = szone->num_huge_entries;
    while (index--) {
        huge = szone->huge_entries + index;
        deallocate_pages(szone, (void *)huge->address, huge->size, szone->debug_flags);
    }
    
    /* destroy tiny regions */
    for (index = 0; index < szone->num_tiny_regions_allocated; ++index)
      if (szone->tiny_regions[index])
        deallocate_pages(szone, szone->tiny_regions[index], TINY_REGION_SIZE, 0);

    /* destroy small regions */
    for (index = 0; index < szone->num_small_regions_allocated; ++index)
      if (szone->small_regions[index])
        deallocate_pages(szone, szone->small_regions[index], SMALL_REGION_SIZE, 0);

    /* destroy region hash rings, if any */
    if (szone->tiny_regions != szone->initial_tiny_regions) {
      size_t size = round_page(szone->num_tiny_regions_allocated * sizeof(region_t));
      deallocate_pages(szone, szone->tiny_regions, size, 0);
    }
    if (szone->small_regions != szone->initial_small_regions) {
      size_t size = round_page(szone->num_small_regions_allocated * sizeof(region_t));
      deallocate_pages(szone, szone->small_regions, size, 0);
    }
    /* Now destroy the separate szone region */
    deallocate_pages(szone, (void *)szone, SZONE_PAGED_SIZE, SCALABLE_MALLOC_ADD_GUARD_PAGES);
}

static size_t
szone_good_size(szone_t *szone, size_t size)
{
    msize_t     msize;
    unsigned    num_pages;
    
    if (size <= 31 * TINY_QUANTUM) {
        // think tiny
        msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
        if (! msize) msize = 1;
        return TINY_BYTES_FOR_MSIZE(msize);
    }
    if (!((szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) && PROTECT_SMALL) && (size < LARGE_THRESHOLD)) {
        // think small
        msize = SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1);
        if (! msize) msize = 1;
        return SMALL_BYTES_FOR_MSIZE(msize);
    } else {
        num_pages = round_page(size) >> vm_page_shift;
        if (!num_pages)
            num_pages = 1; // minimal allocation size for this
        return num_pages << vm_page_shift;
    }
}

unsigned szone_check_counter = 0;
unsigned szone_check_start = 0;
unsigned szone_check_modulo = 1;

static boolean_t
szone_check_all(szone_t *szone, const char *function)
{
    size_t index;

    SZONE_LOCK(szone);
    CHECK_LOCKED(szone, __PRETTY_FUNCTION__);

    /* check tiny regions - chould check region count */
    for (index = 0; index < szone->num_tiny_regions_allocated; ++index) {
      region_t tiny = szone->tiny_regions[index];
      if (tiny && !tiny_check_region(szone, tiny)) {
        SZONE_UNLOCK(szone);
        szone->debug_flags &= ~ CHECK_REGIONS;
        szone_error(szone, "check: tiny region incorrect", NULL,
                    "*** tiny region %d incorrect szone_check_all(%s) counter=%d\n",
                    index, function, szone_check_counter);
        return 0;
      }
    }
    /* check tiny free lists */
    for (index = 0; index < NUM_TINY_SLOTS; ++index) {
      if (!tiny_free_list_check(szone, index)) {
        SZONE_UNLOCK(szone);
        szone->debug_flags &= ~ CHECK_REGIONS;
        szone_error(szone, "check: tiny free list incorrect", NULL,
                    "*** tiny free list incorrect (slot=%d) szone_check_all(%s) counter=%d\n",
                    index, function, szone_check_counter);
        return 0;
      }
    }
    /* check small regions - could check region count */
    for (index = 0; index < szone->num_small_regions_allocated; ++index) {
      region_t small = szone->small_regions[index];
      if (small && !szone_check_small_region(szone, small)) {
        SZONE_UNLOCK(szone);
        szone->debug_flags &= ~ CHECK_REGIONS;
        szone_error(szone, "check: small region incorrect", NULL,
                    "*** small region %d incorrect szone_check_all(%s) counter=%d\n",
                    index, function, szone_check_counter);
        return 0;
      }
    }
    /* check small free lists */
    for (index = 0; index < NUM_SMALL_SLOTS; ++index) {
      if (!small_free_list_check(szone, index)) {
        SZONE_UNLOCK(szone);
        szone->debug_flags &= ~ CHECK_REGIONS;
        szone_error(szone, "check: small free list incorrect", NULL,
                    "*** small free list incorrect (grain=%d) szone_check_all(%s) counter=%d\n",
                    index, function, szone_check_counter);
        return 0;
      }
    }
    SZONE_UNLOCK(szone);
    return 1;
}

static boolean_t
szone_check(szone_t *szone)
{
    if ((++szone_check_counter % 10000) == 0)
        _malloc_printf(ASL_LEVEL_NOTICE, "at szone_check counter=%d\n", szone_check_counter);
    if (szone_check_counter < szone_check_start)
        return 1;
    if (szone_check_counter % szone_check_modulo)
        return 1;
    return szone_check_all(szone, "");
}

static kern_return_t
szone_ptr_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t zone_address, memory_reader_t reader, vm_range_recorder_t recorder)
{
    szone_t             *szone;
    kern_return_t       err;
    
    if (!reader) reader = _szone_default_reader;
    err = reader(task, zone_address, sizeof(szone_t), (void **)&szone);
    if (err) return err;
    err = tiny_in_use_enumerator(task, context, type_mask, szone, reader, recorder);
    if (err) return err;
    err = small_in_use_enumerator(task, context, type_mask, szone, reader, recorder);
    if (err) return err;
    err = large_in_use_enumerator(task, context, type_mask,
      (vm_address_t)szone->large_entries, szone->num_large_entries, reader,
      recorder);
    if (err) return err;
    err = huge_in_use_enumerator(task, context, type_mask,
      (vm_address_t)szone->huge_entries, szone->num_huge_entries, reader,
      recorder);
    return err;
}

// Following method is deprecated:  use scalable_zone_statistics instead
void
scalable_zone_info(malloc_zone_t *zone, unsigned *info_to_fill, unsigned count)
{
    szone_t     *szone = (void *)zone;
    unsigned    info[13];
    
    // We do not lock to facilitate debug
    info[4] = szone->num_tiny_objects;
    info[5] = szone->num_bytes_in_tiny_objects;
    info[6] = szone->num_small_objects;
    info[7] = szone->num_bytes_in_small_objects;
    info[8] = szone->num_large_objects_in_use;
    info[9] = szone->num_bytes_in_large_objects;
    info[10] = szone->num_huge_entries;
    info[11] = szone->num_bytes_in_huge_objects;
    info[12] = szone->debug_flags;
    info[0] = info[4] + info[6] + info[8] + info[10];
    info[1] = info[5] + info[7] + info[9] + info[11];
    info[3] = szone->num_tiny_regions * TINY_REGION_SIZE + szone->num_small_regions * SMALL_REGION_SIZE + info[9] + info[11];
    info[2] = info[3] - szone->tiny_bytes_free_at_end - szone->small_bytes_free_at_end;
    memcpy(info_to_fill, info, sizeof(unsigned)*count);
}

static void
szone_print(szone_t *szone, boolean_t verbose)
{
  unsigned  info[13];
  size_t    index;
  region_t  region;
  
  SZONE_LOCK(szone);
  scalable_zone_info((void *)szone, info, 13);
  _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
                 "Scalable zone %p: inUse=%d(%y) touched=%y allocated=%y flags=%d\n",
                 szone, info[0], info[1], info[2], info[3], info[12]);
  _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
                 "\ttiny=%d(%y) small=%d(%y) large=%d(%y) huge=%d(%y)\n",
                 info[4], info[5], info[6], info[7], info[8], info[9], info[10], info[11]);
  // tiny
  _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
                 "%d tiny regions:\n", szone->num_tiny_regions);
  for (index = 0; index < szone->num_tiny_regions_allocated; ++index) {
    region = szone->tiny_regions[index];
    if (region)
      print_tiny_region(verbose, region, (region == szone->last_tiny_region) ? 
                                         szone->tiny_bytes_free_at_end : 0);
  }
  if (verbose)
    print_tiny_free_list(szone);
  // small
  _malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
                 "%d small regions:\n", szone->num_small_regions);
  for (index = 0; index < szone->num_small_regions_allocated; ++index) {
    region = szone->small_regions[index];
    if (region)
      print_small_region(szone, verbose, region,
                         (region == szone->last_small_region) ? 
                         szone->small_bytes_free_at_end : 0);
  }
  if (verbose)
    print_small_free_list(szone);
  SZONE_UNLOCK(szone);
}

static void
szone_log(malloc_zone_t *zone, void *log_address)
{
    szone_t     *szone = (szone_t *)zone;

    szone->log_address = log_address;
}

static void
szone_force_lock(szone_t *szone)
{
    SZONE_LOCK(szone);
}

static void
szone_force_unlock(szone_t *szone)
{
    SZONE_UNLOCK(szone);
}

boolean_t
scalable_zone_statistics(malloc_zone_t *zone, malloc_statistics_t *stats, unsigned subzone)
{
    szone_t *szone = (szone_t *)zone;
    
    switch (subzone) {
        case 0: 
            stats->blocks_in_use = szone->num_tiny_objects;
            stats->size_in_use = szone->num_bytes_in_tiny_objects;
            stats->size_allocated = szone->num_tiny_regions * TINY_REGION_SIZE;
            stats->max_size_in_use = stats->size_allocated - szone->tiny_bytes_free_at_end;
            return 1;
        case 1: 
            stats->blocks_in_use = szone->num_small_objects;
            stats->size_in_use = szone->num_bytes_in_small_objects;
            stats->size_allocated = szone->num_small_regions * SMALL_REGION_SIZE;
            stats->max_size_in_use = stats->size_allocated - szone->small_bytes_free_at_end;
            return 1;
        case 2:
            stats->blocks_in_use = szone->num_large_objects_in_use;
            stats->size_in_use = szone->num_bytes_in_large_objects;
            stats->max_size_in_use = stats->size_allocated = stats->size_in_use;
            return 1;
        case 3:
            stats->blocks_in_use = szone->num_huge_entries;
            stats->size_in_use = szone->num_bytes_in_huge_objects;
            stats->max_size_in_use = stats->size_allocated = stats->size_in_use;
            return 1;
    }
    return 0;
}

static void
szone_statistics(szone_t *szone, malloc_statistics_t *stats)
{
    size_t      big_and_huge;
    
    stats->blocks_in_use =
      szone->num_tiny_objects +
      szone->num_small_objects +
      szone->num_large_objects_in_use +
      szone->num_huge_entries;
    big_and_huge = szone->num_bytes_in_large_objects + szone->num_bytes_in_huge_objects;
    stats->size_in_use = szone->num_bytes_in_tiny_objects + szone->num_bytes_in_small_objects + big_and_huge;
    stats->max_size_in_use = stats->size_allocated =
      szone->num_tiny_regions * TINY_REGION_SIZE +
      szone->num_small_regions * SMALL_REGION_SIZE +
      big_and_huge ; 

    // Now we account for the untouched areas
    stats->max_size_in_use -= szone->tiny_bytes_free_at_end;
    stats->max_size_in_use -= szone->small_bytes_free_at_end;
}

static const struct malloc_introspection_t szone_introspect = {
    (void *)szone_ptr_in_use_enumerator,
    (void *)szone_good_size,
    (void *)szone_check,
    (void *)szone_print,
    szone_log,
    (void *)szone_force_lock,
    (void *)szone_force_unlock,
    (void *)szone_statistics
}; // marked as const to spare the DATA section

malloc_zone_t *
create_scalable_zone(size_t initial_size, unsigned debug_flags)
{
    szone_t             *szone;

    /*
     * Sanity-check our build-time assumptions about the size of a page.
     * Since we have sized various things assuming the default page size,
     * attempting to determine it dynamically is not useful.
     */
    if ((vm_page_size != _vm_page_size) || (vm_page_shift != _vm_page_shift)) {
        malloc_printf("*** FATAL ERROR - machine page size does not match our assumptions.\n");
        exit(-1);
    }

    /* get memory for the zone, which is now separate from any region.
       add guard pages to prevent walking from any other vm allocations
       to here and overwriting the function pointers in basic_zone. */
    szone = allocate_pages(NULL, SZONE_PAGED_SIZE, 0, 
                           SCALABLE_MALLOC_ADD_GUARD_PAGES, 
                           VM_MEMORY_MALLOC);
    if (!szone)
        return NULL;
    /* set up the szone structure */
    szone->tiny_regions = szone->initial_tiny_regions;
    szone->small_regions = szone->initial_small_regions;
    szone->num_tiny_regions_allocated = INITIAL_NUM_REGIONS;
    szone->num_small_regions_allocated = INITIAL_NUM_REGIONS;
    szone->basic_zone.version = 3;
    szone->basic_zone.size = (void *)szone_size;
    szone->basic_zone.malloc = (void *)szone_malloc;
    szone->basic_zone.calloc = (void *)szone_calloc;
    szone->basic_zone.valloc = (void *)szone_valloc;
    szone->basic_zone.free = (void *)szone_free;
    szone->basic_zone.realloc = (void *)szone_realloc;
    szone->basic_zone.destroy = (void *)szone_destroy;
    szone->basic_zone.batch_malloc = (void *)szone_batch_malloc;
    szone->basic_zone.batch_free = (void *)szone_batch_free;
    szone->basic_zone.introspect = (struct malloc_introspection_t *)&szone_introspect;
    szone->debug_flags = debug_flags;
    LOCK_INIT(szone->lock);

#if 0
#warning CHECK_REGIONS enabled
    debug_flags |= CHECK_REGIONS;
#endif
#if 0
#warning LOG enabled
    szone->log_address = ~0;
#endif
    CHECK(szone, __PRETTY_FUNCTION__);
    return (malloc_zone_t *)szone;
}

/********* Support code for emacs unexec ************/

/* History of freezedry version numbers:
 *
 * 1) Old malloc (before the scalable malloc implementation in this file
 *    existed).
 * 2) Original freezedrying code for scalable malloc.  This code was apparently
 *    based on the old freezedrying code and was fundamentally flawed in its
 *    assumption that tracking allocated memory regions was adequate to fake
 *    operations on freezedried memory.  This doesn't work, since scalable
 *    malloc does not store flags in front of large page-aligned allocations.
 * 3) Original szone-based freezedrying code.
 * 4) Fresher malloc with tiny zone
 * 5) 32/64bit compatible malloc
 * 6) Metadata within 1MB and 8MB region for tiny and small
 *
 * No version backward compatibility is provided, but the version number does
 * make it possible for malloc_jumpstart() to return an error if the application
 * was freezedried with an older version of malloc.
 */
#define MALLOC_FREEZEDRY_VERSION 6

typedef struct {
    unsigned version;
    unsigned nszones;
    szone_t *szones;
} malloc_frozen;

static void *
frozen_malloc(szone_t *zone, size_t new_size)
{
    return malloc(new_size);
}

static void *
frozen_calloc(szone_t *zone, size_t num_items, size_t size)
{
    return calloc(num_items, size);
}

static void *
frozen_valloc(szone_t *zone, size_t new_size)
{
    return valloc(new_size);
}

static void *
frozen_realloc(szone_t *zone, void *ptr, size_t new_size)
{
    size_t      old_size = szone_size(zone, ptr);
    void        *new_ptr;
    
    if (new_size <= old_size) {
        return ptr;
    }
    new_ptr = malloc(new_size);
    if (old_size > 0) {
        memcpy(new_ptr, ptr, old_size);
    }
    return new_ptr;
}

static void
frozen_free(szone_t *zone, void *ptr)
{
}

static void
frozen_destroy(szone_t *zone)
{
}

/********* Pseudo-private API for emacs unexec ************/

/*
 * malloc_freezedry() records all of the szones in use, so that they can be
 * partially reconstituted by malloc_jumpstart().  Due to the differences
 * between reconstituted memory regions and those created by the szone code,
 * care is taken not to reallocate from the freezedried memory, except in the
 * case of a non-growing realloc().
 *
 * Due to the flexibility provided by the zone registration mechanism, it is
 * impossible to implement generic freezedrying for any zone type.  This code
 * only handles applications that use the szone allocator, so malloc_freezedry()
 * returns 0 (error) if any non-szone zones are encountered.
 */

uintptr_t
malloc_freezedry(void)
{
    extern unsigned malloc_num_zones;
    extern malloc_zone_t **malloc_zones;
    malloc_frozen *data;
    unsigned i;

    /* Allocate space in which to store the freezedry state. */
    data = (malloc_frozen *) malloc(sizeof(malloc_frozen));

    /* Set freezedry version number so that malloc_jumpstart() can check for compatibility. */
    data->version = MALLOC_FREEZEDRY_VERSION;

    /* Allocate the array of szone pointers. */
    data->nszones = malloc_num_zones;
    data->szones = (szone_t *) calloc(malloc_num_zones, sizeof(szone_t));

    /*
     * Fill in the array of szone structures.  They are copied rather than
     * referenced, since the originals are likely to be clobbered during malloc
     * initialization.
     */
    for (i = 0; i < malloc_num_zones; i++) {
        if (strcmp(malloc_zones[i]->zone_name, "DefaultMallocZone")) {
            /* Unknown zone type. */
            free(data->szones);
            free(data);
            return 0;
        }
        memcpy(&data->szones[i], malloc_zones[i], sizeof(szone_t));
    }

    return((uintptr_t)data);
}

int
malloc_jumpstart(uintptr_t cookie)
{
    malloc_frozen *data = (malloc_frozen *)cookie;
    unsigned i;

    if (data->version != MALLOC_FREEZEDRY_VERSION) {
        /* Unsupported freezedry version. */
        return 1;
    }

    for (i = 0; i < data->nszones; i++) {
        /* Set function pointers.  Even the functions that stay the same must be
         * set, since there are no guarantees that they will be mapped to the
         * same addresses. */
        data->szones[i].basic_zone.size = (void *) szone_size;
        data->szones[i].basic_zone.malloc = (void *) frozen_malloc;
        data->szones[i].basic_zone.calloc = (void *) frozen_calloc;
        data->szones[i].basic_zone.valloc = (void *) frozen_valloc;
        data->szones[i].basic_zone.free = (void *) frozen_free;
        data->szones[i].basic_zone.realloc = (void *) frozen_realloc;
        data->szones[i].basic_zone.destroy = (void *) frozen_destroy;
        data->szones[i].basic_zone.introspect = (struct malloc_introspection_t *)&szone_introspect;

        /* Register the freezedried zone. */
        malloc_zone_register(&data->szones[i].basic_zone);
    }

    return 0;
}