xnu-3248.30.4.tar.gz

[apple/xnu.git] / osfmk / vm / vm_purgeable.c

/*
 * Copyright (c) 2007 Apple 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@
 */

#include <kern/sched_prim.h>
#include <kern/ledger.h>

#include <libkern/OSDebug.h>

#include <mach/mach_types.h>

#include <machine/limits.h>

#include <vm/vm_compressor_pager.h>
#include <vm/vm_kern.h>                         /* kmem_alloc */
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_protos.h>
#include <vm/vm_purgeable_internal.h>

#include <sys/kdebug.h>

extern vm_pressure_level_t memorystatus_vm_pressure_level;

struct token {
        token_cnt_t     count;
        token_idx_t     prev;
        token_idx_t     next;
};

struct token    *tokens;
token_idx_t     token_q_max_cnt = 0;
vm_size_t       token_q_cur_size = 0;

token_idx_t     token_free_idx = 0;             /* head of free queue */
token_idx_t     token_init_idx = 1;             /* token 0 is reserved!! */
int32_t         token_new_pagecount = 0;        /* count of pages that will
                                                 * be added onto token queue */

int             available_for_purge = 0;        /* increase when ripe token
                                                 * added, decrease when ripe
                                                 * token removed.
                                                 * protected by page_queue_lock 
                                                 */

static int token_q_allocating = 0;              /* flag for singlethreading 
                                                 * allocator */

struct purgeable_q purgeable_queues[PURGEABLE_Q_TYPE_MAX];
queue_head_t purgeable_nonvolatile_queue;
int purgeable_nonvolatile_count;

decl_lck_mtx_data(,vm_purgeable_queue_lock)

static token_idx_t vm_purgeable_token_remove_first(purgeable_q_t queue);

static void vm_purgeable_stats_helper(vm_purgeable_stat_t *stat, purgeable_q_t queue, int group, task_t target_task);

void vm_purgeable_nonvolatile_owner_update(task_t       owner,
                                           int          delta);
void vm_purgeable_volatile_owner_update(task_t          owner,
                                        int             delta);


#if MACH_ASSERT
static void
vm_purgeable_token_check_queue(purgeable_q_t queue)
{
        int             token_cnt = 0, page_cnt = 0;
        token_idx_t     token = queue->token_q_head;
        token_idx_t     unripe = 0;
        int             our_inactive_count;

#if DEVELOPMENT
        static unsigned lightweight_check = 0;

        /*
         * Due to performance impact, only perform this check
         * every 100 times on DEVELOPMENT kernels.
         */
        if (lightweight_check++ < 100) {
                return;
        }

        lightweight_check = 0;
#endif

        while (token) {
                if (tokens[token].count != 0) {
                        assert(queue->token_q_unripe);
                        if (unripe == 0) {
                                assert(token == queue->token_q_unripe);
                                unripe = token;
                        }
                        page_cnt += tokens[token].count;
                }
                if (tokens[token].next == 0)
                        assert(queue->token_q_tail == token);

                token_cnt++;
                token = tokens[token].next;
        }

        if (unripe)
                assert(queue->token_q_unripe == unripe);
        assert(token_cnt == queue->debug_count_tokens);
        
        /* obsolete queue doesn't maintain token counts */
        if(queue->type != PURGEABLE_Q_TYPE_OBSOLETE)
        {
                our_inactive_count = page_cnt + queue->new_pages + token_new_pagecount;
                assert(our_inactive_count >= 0);
                assert((uint32_t) our_inactive_count == vm_page_inactive_count - vm_page_cleaned_count);
        }
}
#endif

/*
 * Add a token. Allocate token queue memory if necessary.
 * Call with page queue locked.
 */
kern_return_t
vm_purgeable_token_add(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        
        /* new token */
        token_idx_t     token;
        enum purgeable_q_type i;

find_available_token:

        if (token_free_idx) {                           /* unused tokens available */
                token = token_free_idx;
                token_free_idx = tokens[token_free_idx].next;
        } else if (token_init_idx < token_q_max_cnt) {  /* lazy token array init */
                token = token_init_idx;
                token_init_idx++;
        } else {                                        /* allocate more memory */
                /* Wait if another thread is inside the memory alloc section */
                while(token_q_allocating) {
                        wait_result_t res = lck_mtx_sleep(&vm_page_queue_lock,
                                                          LCK_SLEEP_DEFAULT,
                                                          (event_t)&token_q_allocating,
                                                          THREAD_UNINT);
                        if(res != THREAD_AWAKENED) return KERN_ABORTED;
                };
                
                /* Check whether memory is still maxed out */
                if(token_init_idx < token_q_max_cnt)
                        goto find_available_token;
                
                /* Still no memory. Allocate some. */
                token_q_allocating = 1;
                
                /* Drop page queue lock so we can allocate */
                vm_page_unlock_queues();
                
                struct token *new_loc;
                vm_size_t alloc_size = token_q_cur_size + PAGE_SIZE;
                kern_return_t result;
                
                if (alloc_size / sizeof (struct token) > TOKEN_COUNT_MAX) {
                        result = KERN_RESOURCE_SHORTAGE;
                } else {
                        if (token_q_cur_size) {
                                result = kmem_realloc(kernel_map,
                                                      (vm_offset_t) tokens,
                                                      token_q_cur_size,
                                                      (vm_offset_t *) &new_loc,
                                                      alloc_size, VM_KERN_MEMORY_OSFMK);
                        } else {
                                result = kmem_alloc(kernel_map,
                                                    (vm_offset_t *) &new_loc,
                                                    alloc_size, VM_KERN_MEMORY_OSFMK);
                        }
                }
                
                vm_page_lock_queues();
                
                if (result) {
                        /* Unblock waiting threads */
                        token_q_allocating = 0;
                        thread_wakeup((event_t)&token_q_allocating);
                        return result;
                }
                
                /* If we get here, we allocated new memory. Update pointers and
                 * dealloc old range */
                struct token *old_tokens=tokens;
                tokens=new_loc;
                vm_size_t old_token_q_cur_size=token_q_cur_size;
                token_q_cur_size=alloc_size;
                token_q_max_cnt = (token_idx_t) (token_q_cur_size /
                                                 sizeof(struct token));
                assert (token_init_idx < token_q_max_cnt);      /* We must have a free token now */
                
                if (old_token_q_cur_size) {     /* clean up old mapping */
                        vm_page_unlock_queues();
                        /* kmem_realloc leaves the old region mapped. Get rid of it. */
                        kmem_free(kernel_map, (vm_offset_t)old_tokens, old_token_q_cur_size);
                        vm_page_lock_queues();
                }
                
                /* Unblock waiting threads */
                token_q_allocating = 0;
                thread_wakeup((event_t)&token_q_allocating);
                
                goto find_available_token;
        }
        
        assert (token);
        
        /*
         * the new pagecount we got need to be applied to all queues except
         * obsolete
         */
        for (i = PURGEABLE_Q_TYPE_FIFO; i < PURGEABLE_Q_TYPE_MAX; i++) {
                int64_t pages = purgeable_queues[i].new_pages += token_new_pagecount;
                assert(pages >= 0);
                assert(pages <= TOKEN_COUNT_MAX);
                purgeable_queues[i].new_pages = (int32_t) pages;
                assert(purgeable_queues[i].new_pages == pages);
        }
        token_new_pagecount = 0;

        /* set token counter value */
        if (queue->type != PURGEABLE_Q_TYPE_OBSOLETE)
                tokens[token].count = queue->new_pages;
        else
                tokens[token].count = 0;        /* all obsolete items are
                                                 * ripe immediately */
        queue->new_pages = 0;

        /* put token on token counter list */
        tokens[token].next = 0;
        if (queue->token_q_tail == 0) {
                assert(queue->token_q_head == 0 && queue->token_q_unripe == 0);
                queue->token_q_head = token;
                tokens[token].prev = 0;
        } else {
                tokens[queue->token_q_tail].next = token;
                tokens[token].prev = queue->token_q_tail;
        }
        if (queue->token_q_unripe == 0) {       /* only ripe tokens (token
                                                 * count == 0) in queue */
                if (tokens[token].count > 0)
                        queue->token_q_unripe = token;  /* first unripe token */
                else
                        available_for_purge++;  /* added a ripe token?
                                                 * increase available count */
        }
        queue->token_q_tail = token;

#if MACH_ASSERT
        queue->debug_count_tokens++;
        /* Check both queues, since we modified the new_pages count on each */
        vm_purgeable_token_check_queue(&purgeable_queues[PURGEABLE_Q_TYPE_FIFO]);
        vm_purgeable_token_check_queue(&purgeable_queues[PURGEABLE_Q_TYPE_LIFO]);

        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, TOKEN_ADD)),
                              queue->type,
                              tokens[token].count,      /* num pages on token
                                                         * (last token) */
                              queue->debug_count_tokens,
                              0,
                              0);
#endif

        return KERN_SUCCESS;
}

/*
 * Remove first token from queue and return its index. Add its count to the
 * count of the next token.
 * Call with page queue locked. 
 */
static token_idx_t 
vm_purgeable_token_remove_first(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        
        token_idx_t     token;
        token = queue->token_q_head;

        assert(token);

        if (token) {
                assert(queue->token_q_tail);
                if (queue->token_q_head == queue->token_q_unripe) {
                        /* no ripe tokens... must move unripe pointer */
                        queue->token_q_unripe = tokens[token].next;
                } else {
                        /* we're removing a ripe token. decrease count */
                        available_for_purge--;
                        assert(available_for_purge >= 0);
                }

                if (queue->token_q_tail == queue->token_q_head)
                        assert(tokens[token].next == 0);

                queue->token_q_head = tokens[token].next;
                if (queue->token_q_head) {
                        tokens[queue->token_q_head].count += tokens[token].count;
                        tokens[queue->token_q_head].prev = 0;
                } else {
                        /* currently no other tokens in the queue */
                        /*
                         * the page count must be added to the next newly
                         * created token
                         */
                        queue->new_pages += tokens[token].count;
                        /* if head is zero, tail is too */
                        queue->token_q_tail = 0;
                }

#if MACH_ASSERT
                queue->debug_count_tokens--;
                vm_purgeable_token_check_queue(queue);

                KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, TOKEN_DELETE)),
                                      queue->type,
                                      tokens[queue->token_q_head].count,        /* num pages on new
                                                                                 * first token */
                                      token_new_pagecount,      /* num pages waiting for
                                                                 * next token */
                                      available_for_purge,
                                      0);
#endif
        }
        return token;
}

static token_idx_t 
vm_purgeable_token_remove_last(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        
        token_idx_t     token;
        token = queue->token_q_tail;

        assert(token);

        if (token) {
                assert(queue->token_q_head);

                if (queue->token_q_tail == queue->token_q_head)
                        assert(tokens[token].next == 0);

                if (queue->token_q_unripe == 0) {
                        /* we're removing a ripe token. decrease count */
                        available_for_purge--;
                        assert(available_for_purge >= 0);
                } else if (queue->token_q_unripe == token) {
                        /* we're removing the only unripe token */
                        queue->token_q_unripe = 0;
                }
                        
                if (token == queue->token_q_head) {
                        /* token is the last one in the queue */
                        queue->token_q_head = 0;
                        queue->token_q_tail = 0;
                } else {
                        token_idx_t new_tail;

                        new_tail = tokens[token].prev;

                        assert(new_tail);
                        assert(tokens[new_tail].next == token);

                        queue->token_q_tail = new_tail;
                        tokens[new_tail].next = 0;
                }

                queue->new_pages += tokens[token].count;

#if MACH_ASSERT
                queue->debug_count_tokens--;
                vm_purgeable_token_check_queue(queue);

                KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, TOKEN_DELETE)),
                                      queue->type,
                                      tokens[queue->token_q_head].count,        /* num pages on new
                                                                                 * first token */
                                      token_new_pagecount,      /* num pages waiting for
                                                                 * next token */
                                      available_for_purge,
                                      0);
#endif
        }
        return token;
}

/* 
 * Delete first token from queue. Return token to token queue.
 * Call with page queue locked. 
 */
void
vm_purgeable_token_delete_first(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        token_idx_t     token = vm_purgeable_token_remove_first(queue);

        if (token) {
                /* stick removed token on free queue */
                tokens[token].next = token_free_idx;
                tokens[token].prev = 0;
                token_free_idx = token;
        }
}

void
vm_purgeable_token_delete_last(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        token_idx_t     token = vm_purgeable_token_remove_last(queue);

        if (token) {
                /* stick removed token on free queue */
                tokens[token].next = token_free_idx;
                tokens[token].prev = 0;
                token_free_idx = token;
        }
}


/* Call with page queue locked. */
void
vm_purgeable_q_advance_all()
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        
        /* check queue counters - if they get really large, scale them back.
         * They tend to get that large when there is no purgeable queue action */
        int i;
        if(token_new_pagecount > (TOKEN_NEW_PAGECOUNT_MAX >> 1))        /* a system idling years might get there */
        {
                for (i = PURGEABLE_Q_TYPE_FIFO; i < PURGEABLE_Q_TYPE_MAX; i++) {
                        int64_t pages = purgeable_queues[i].new_pages += token_new_pagecount;
                        assert(pages >= 0);
                        assert(pages <= TOKEN_COUNT_MAX);
                        purgeable_queues[i].new_pages = (int32_t) pages;
                        assert(purgeable_queues[i].new_pages == pages);
                }
                token_new_pagecount = 0;
        }
        
        /*
         * Decrement token counters. A token counter can be zero, this means the
         * object is ripe to be purged. It is not purged immediately, because that
         * could cause several objects to be purged even if purging one would satisfy
         * the memory needs. Instead, the pageout thread purges one after the other
         * by calling vm_purgeable_object_purge_one and then rechecking the memory
         * balance.
         *
         * No need to advance obsolete queue - all items are ripe there,
         * always
         */
        for (i = PURGEABLE_Q_TYPE_FIFO; i < PURGEABLE_Q_TYPE_MAX; i++) {
                purgeable_q_t queue = &purgeable_queues[i];
                uint32_t num_pages = 1;
                
                /* Iterate over tokens as long as there are unripe tokens. */
                while (queue->token_q_unripe) {
                        if (tokens[queue->token_q_unripe].count && num_pages)
                        {
                                tokens[queue->token_q_unripe].count -= 1;
                                num_pages -= 1;
                        }

                        if (tokens[queue->token_q_unripe].count == 0) {
                                queue->token_q_unripe = tokens[queue->token_q_unripe].next;
                                available_for_purge++;
                                KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, TOKEN_RIPEN)),
                                                      queue->type,
                                                      tokens[queue->token_q_head].count,        /* num pages on new
                                                                                         * first token */
                                                      0,
                                                      available_for_purge,
                                                      0);
                                continue;       /* One token ripened. Make sure to
                                                 * check the next. */
                        }
                        if (num_pages == 0)
                                break;  /* Current token not ripe and no more pages.
                                         * Work done. */
                }

                /*
                 * if there are no unripe tokens in the queue, decrement the
                 * new_pages counter instead new_pages can be negative, but must be
                 * canceled out by token_new_pagecount -- since inactive queue as a
                 * whole always contains a nonnegative number of pages
                 */
                if (!queue->token_q_unripe) {
                        queue->new_pages -= num_pages;
                        assert((int32_t) token_new_pagecount + queue->new_pages >= 0);
                }
#if MACH_ASSERT
                vm_purgeable_token_check_queue(queue);
#endif
        }
}

/*
 * grab any ripe object and purge it obsolete queue first. then, go through
 * each volatile group. Select a queue with a ripe token.
 * Start with first group (0)
 * 1. Look at queue. Is there an object?
 *   Yes - purge it. Remove token.
 *   No - check other queue. Is there an object?
 *     No - increment group, then go to (1)
 *     Yes - purge it. Remove token. If there is no ripe token, remove ripe
 *      token from other queue and migrate unripe token from this
 *      queue to other queue.
 * Call with page queue locked.
 */
static void
vm_purgeable_token_remove_ripe(purgeable_q_t queue)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        assert(queue->token_q_head && tokens[queue->token_q_head].count == 0);
        /* return token to free list. advance token list. */
        token_idx_t     new_head = tokens[queue->token_q_head].next;
        tokens[queue->token_q_head].next = token_free_idx;
        tokens[queue->token_q_head].prev = 0;
        token_free_idx = queue->token_q_head;
        queue->token_q_head = new_head;
        tokens[new_head].prev = 0;
        if (new_head == 0)
                queue->token_q_tail = 0;

#if MACH_ASSERT
        queue->debug_count_tokens--;
        vm_purgeable_token_check_queue(queue);
#endif

        available_for_purge--;
        assert(available_for_purge >= 0);
}

/*
 * Delete a ripe token from the given queue. If there are no ripe tokens on
 * that queue, delete a ripe token from queue2, and migrate an unripe token
 * from queue to queue2
 * Call with page queue locked.
 */
static void
vm_purgeable_token_choose_and_delete_ripe(purgeable_q_t queue, purgeable_q_t queue2)
{
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        assert(queue->token_q_head);

        if (tokens[queue->token_q_head].count == 0) {
                /* This queue has a ripe token. Remove. */
                vm_purgeable_token_remove_ripe(queue);
        } else {
                assert(queue2);
                /*
                 * queue2 must have a ripe token. Remove, and migrate one
                 * from queue to queue2.
                 */
                vm_purgeable_token_remove_ripe(queue2);
                /* migrate unripe token */
                token_idx_t     token;
                token_cnt_t     count;

                /* remove token from queue1 */
                assert(queue->token_q_unripe == queue->token_q_head);   /* queue1 had no unripe
                                                                         * tokens, remember? */
                token = vm_purgeable_token_remove_first(queue);
                assert(token);

                count = tokens[token].count;

                /* migrate to queue2 */
                /* go to migration target loc */

                token_idx_t token_to_insert_before = queue2->token_q_head, token_to_insert_after;

                while (token_to_insert_before != 0 && count > tokens[token_to_insert_before].count) {
                        count -= tokens[token_to_insert_before].count;
                        token_to_insert_before = tokens[token_to_insert_before].next;
                }

                /* token_to_insert_before is now set correctly */
        
                /* should the inserted token become the first unripe token? */
                if ((token_to_insert_before == queue2->token_q_unripe) || (queue2->token_q_unripe == 0))
                        queue2->token_q_unripe = token; /* if so, must update unripe pointer */

                /*
                 * insert token.
                 * if inserting at end, reduce new_pages by that value;
                 * otherwise, reduce counter of next token
                 */

                tokens[token].count = count;

                if (token_to_insert_before != 0) {
                        token_to_insert_after = tokens[token_to_insert_before].prev;

                        tokens[token].next = token_to_insert_before;
                        tokens[token_to_insert_before].prev = token;

                        assert(tokens[token_to_insert_before].count >= count);
                        tokens[token_to_insert_before].count -= count;
                } else {
                        /* if we ran off the end of the list, the token to insert after is the tail */
                        token_to_insert_after = queue2->token_q_tail;

                        tokens[token].next = 0;
                        queue2->token_q_tail = token;

                        assert(queue2->new_pages >= (int32_t) count);
                        queue2->new_pages -= count;
                }

                if (token_to_insert_after != 0) {
                        tokens[token].prev = token_to_insert_after;
                        tokens[token_to_insert_after].next = token;
                } else {
                        /* is this case possible? */
                        tokens[token].prev = 0;
                        queue2->token_q_head = token;
                }

#if MACH_ASSERT
                queue2->debug_count_tokens++;
                vm_purgeable_token_check_queue(queue2);
#endif
        }
}

/* Find an object that can be locked. Returns locked object. */
/* Call with purgeable queue locked. */
static vm_object_t
vm_purgeable_object_find_and_lock(
        purgeable_q_t   queue,
        int             group,
        boolean_t       pick_ripe)
{
        vm_object_t     object, best_object;
        int             object_task_importance;
        int             best_object_task_importance;
        int             best_object_skipped;
        int             num_objects_skipped;
        int             try_lock_failed = 0;
        int             try_lock_succeeded = 0;
        task_t          owner;

        best_object = VM_OBJECT_NULL;
        best_object_task_importance = INT_MAX;

        lck_mtx_assert(&vm_purgeable_queue_lock, LCK_MTX_ASSERT_OWNED);
        /*
         * Usually we would pick the first element from a queue. However, we
         * might not be able to get a lock on it, in which case we try the
         * remaining elements in order.
         */

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, (MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE_LOOP) | DBG_FUNC_START),
                              pick_ripe,
                              group,
                              VM_KERNEL_UNSLIDE_OR_PERM(queue),
                              0,
                              0);

        num_objects_skipped = 0;
        for (object = (vm_object_t) queue_first(&queue->objq[group]);
             !queue_end(&queue->objq[group], (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq),
                num_objects_skipped++) {

                /*
                 * To prevent us looping for an excessively long time, choose
                 * the best object we've seen after looking at PURGEABLE_LOOP_MAX elements.
                 * If we haven't seen an eligible object after PURGEABLE_LOOP_MAX elements,
                 * we keep going until we find the first eligible object.
                 */
                if ((num_objects_skipped >= PURGEABLE_LOOP_MAX) && (best_object != NULL)) {
                        break;
                }

                if (pick_ripe &&
                    ! object->purgeable_when_ripe) {
                        /* we want an object that has a ripe token */
                        continue;
                }

                object_task_importance = 0;

                owner = object->vo_purgeable_owner;
                if (owner) {
                        object_task_importance = task_importance_estimate(owner);
                }

                if (object_task_importance < best_object_task_importance) {
                        if (vm_object_lock_try(object)) {
                                try_lock_succeeded++;
                                if (best_object != VM_OBJECT_NULL) {
                                        /* forget about previous best object */
                                        vm_object_unlock(best_object);
                                }
                                best_object = object;
                                best_object_task_importance = object_task_importance;
                                best_object_skipped = num_objects_skipped;
                                if (best_object_task_importance == 0) {
                                        /* can't get any better: stop looking */
                                        break;
                                }
                        } else {
                                try_lock_failed++;
                        }
                }
        }

        KERNEL_DEBUG_CONSTANT_IST(KDEBUG_TRACE, (MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE_LOOP) | DBG_FUNC_END),
                              num_objects_skipped, /* considered objects */
                              try_lock_failed,
                              try_lock_succeeded,
                              VM_KERNEL_UNSLIDE_OR_PERM(best_object),
                              ((best_object == NULL) ? 0 : best_object->resident_page_count));

        object = best_object;

        if (object == VM_OBJECT_NULL) {
                return VM_OBJECT_NULL;
        }

        /* Locked. Great. We'll take it. Remove and return. */
//      printf("FOUND PURGEABLE object %p skipped %d\n", object, num_objects_skipped);

        vm_object_lock_assert_exclusive(object);

        queue_remove(&queue->objq[group], object,
                     vm_object_t, objq);
        object->objq.next = NULL;
        object->objq.prev = NULL;
        object->purgeable_queue_type = PURGEABLE_Q_TYPE_MAX;
        object->purgeable_queue_group = 0;
        /* one less volatile object for this object's owner */
        vm_purgeable_volatile_owner_update(object->vo_purgeable_owner, -1);

#if DEBUG
        object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */

        /* keep queue of non-volatile objects */
        queue_enter(&purgeable_nonvolatile_queue, object,
                    vm_object_t, objq);
        assert(purgeable_nonvolatile_count >= 0);
        purgeable_nonvolatile_count++;
        assert(purgeable_nonvolatile_count > 0);
        /* one more nonvolatile object for this object's owner */
        vm_purgeable_nonvolatile_owner_update(object->vo_purgeable_owner, +1);

#if MACH_ASSERT
        queue->debug_count_objects--;
#endif
        return object;
}

/* Can be called without holding locks */
void
vm_purgeable_object_purge_all(void)
{
        enum purgeable_q_type i;
        int             group;
        vm_object_t     object;
        unsigned int    purged_count;
        uint32_t        collisions;

        purged_count = 0;
        collisions = 0;

restart:
        lck_mtx_lock(&vm_purgeable_queue_lock);
        /* Cycle through all queues */
        for (i = PURGEABLE_Q_TYPE_OBSOLETE; i < PURGEABLE_Q_TYPE_MAX; i++) {
                purgeable_q_t   queue;

                queue = &purgeable_queues[i];

                /*
                 * Look through all groups, starting from the lowest. If
                 * we find an object in that group, try to lock it (this can
                 * fail). If locking is successful, we can drop the queue
                 * lock, remove a token and then purge the object.
                 */
                for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                        while (!queue_empty(&queue->objq[group])) {
                                object = vm_purgeable_object_find_and_lock(queue, group, FALSE);
                                if (object == VM_OBJECT_NULL) {
                                        lck_mtx_unlock(&vm_purgeable_queue_lock);
                                        mutex_pause(collisions++);
                                        goto restart;
                                }

                                lck_mtx_unlock(&vm_purgeable_queue_lock);
                                
                                /* Lock the page queue here so we don't hold it
                                 * over the whole, legthy operation */
                                if (object->purgeable_when_ripe) {
                                        vm_page_lock_queues();
                                        vm_purgeable_token_remove_first(queue);
                                        vm_page_unlock_queues();
                                }
                                
                                (void) vm_object_purge(object, 0);
                                assert(object->purgable == VM_PURGABLE_EMPTY);
                                /* no change in purgeable accounting */

                                vm_object_unlock(object);
                                purged_count++;
                                goto restart;
                        }
                        assert(queue->debug_count_objects >= 0);
                }
        }
        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE_ALL)),
                              purged_count, /* # of purged objects */
                              0,
                              available_for_purge,
                              0,
                              0);
        lck_mtx_unlock(&vm_purgeable_queue_lock);
        return;
}

boolean_t
vm_purgeable_object_purge_one_unlocked(
        int     force_purge_below_group)
{
        boolean_t       retval;

        vm_page_lock_queues();
        retval = vm_purgeable_object_purge_one(force_purge_below_group, 0);
        vm_page_unlock_queues();

        return retval;
}

boolean_t
vm_purgeable_object_purge_one(
        int     force_purge_below_group,
        int     flags)
{
        enum purgeable_q_type i;
        int             group;
        vm_object_t     object = 0;
        purgeable_q_t   queue, queue2;
        boolean_t       forced_purge;

        /* Need the page queue lock since we'll be changing the token queue. */
#if MACH_ASSERT
        lck_mtx_assert(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
#endif
        lck_mtx_lock(&vm_purgeable_queue_lock);
        
        /* Cycle through all queues */
        for (i = PURGEABLE_Q_TYPE_OBSOLETE; i < PURGEABLE_Q_TYPE_MAX; i++) {
                queue = &purgeable_queues[i];

                if (force_purge_below_group == 0) {
                        /*
                         * Are there any ripe tokens on this queue? If yes,
                         * we'll find an object to purge there
                         */
                        if (!queue->token_q_head) {
                                /* no token: look at next purgeable queue */
                                continue;
                        }

                        if (tokens[queue->token_q_head].count != 0) {
                                /* no ripe token: next queue */
                                continue;
                        }
                }

                /*
                 * Now look through all groups, starting from the lowest. If
                 * we find an object in that group, try to lock it (this can
                 * fail). If locking is successful, we can drop the queue
                 * lock, remove a token and then purge the object.
                 */
                for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                        if (!queue->token_q_head ||
                            tokens[queue->token_q_head].count != 0) {
                                /* no tokens or no ripe tokens */

                                if (group >= force_purge_below_group) {
                                        /* no more groups to force-purge */
                                        break;
                                }

                                /*
                                 * Try and purge an object in this group
                                 * even though no tokens are ripe.
                                 */
                                if (!queue_empty(&queue->objq[group]) &&
                                    (object = vm_purgeable_object_find_and_lock(queue, group, FALSE))) {
                                        lck_mtx_unlock(&vm_purgeable_queue_lock);
                                        if (object->purgeable_when_ripe) {
                                                vm_purgeable_token_delete_first(queue);
                                        }
                                        forced_purge = TRUE;
                                        goto purge_now;
                                }

                                /* nothing to purge in this group: next group */
                                continue;
                        }
                        if (!queue_empty(&queue->objq[group]) && 
                            (object = vm_purgeable_object_find_and_lock(queue, group, TRUE))) {
                                lck_mtx_unlock(&vm_purgeable_queue_lock);
                                if (object->purgeable_when_ripe) {
                                        vm_purgeable_token_choose_and_delete_ripe(queue, 0);
                                }
                                forced_purge = FALSE;
                                goto purge_now;
                        }
                        if (i != PURGEABLE_Q_TYPE_OBSOLETE) { 
                                /* This is the token migration case, and it works between
                                 * FIFO and LIFO only */
                                queue2 = &purgeable_queues[i != PURGEABLE_Q_TYPE_FIFO ? 
                                                           PURGEABLE_Q_TYPE_FIFO : 
                                                           PURGEABLE_Q_TYPE_LIFO];

                                if (!queue_empty(&queue2->objq[group]) && 
                                    (object = vm_purgeable_object_find_and_lock(queue2, group, TRUE))) {
                                        lck_mtx_unlock(&vm_purgeable_queue_lock);
                                        if (object->purgeable_when_ripe) {
                                                vm_purgeable_token_choose_and_delete_ripe(queue2, queue);
                                        }
                                        forced_purge = FALSE;
                                        goto purge_now;
                                }
                        }
                        assert(queue->debug_count_objects >= 0);
                }
        }
        /*
         * because we have to do a try_lock on the objects which could fail,
         * we could end up with no object to purge at this time, even though
         * we have objects in a purgeable state
         */
        lck_mtx_unlock(&vm_purgeable_queue_lock);
        return FALSE;

purge_now:

        assert(object);
        vm_page_unlock_queues();  /* Unlock for call to vm_object_purge() */
//      printf("%sPURGING object %p task %p importance %d queue %d group %d force_purge_below_group %d memorystatus_vm_pressure_level %d\n", forced_purge ? "FORCED " : "", object, object->vo_purgeable_owner, task_importance_estimate(object->vo_purgeable_owner), i, group, force_purge_below_group, memorystatus_vm_pressure_level);
        (void) vm_object_purge(object, flags);
        assert(object->purgable == VM_PURGABLE_EMPTY);
        /* no change in purgeable accounting */
        vm_object_unlock(object);
        vm_page_lock_queues();

        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE)),
                              object,   /* purged object */
                              0,
                              available_for_purge,
                              0,
                              0);
        
        return TRUE;
}

/* Called with object lock held */
void
vm_purgeable_object_add(vm_object_t object, purgeable_q_t queue, int group)
{
        vm_object_lock_assert_exclusive(object);
        lck_mtx_lock(&vm_purgeable_queue_lock);

        assert(object->objq.next != NULL);
        assert(object->objq.prev != NULL);
        queue_remove(&purgeable_nonvolatile_queue, object,
                     vm_object_t, objq);
        object->objq.next = NULL;
        object->objq.prev = NULL;
        assert(purgeable_nonvolatile_count > 0);
        purgeable_nonvolatile_count--;
        assert(purgeable_nonvolatile_count >= 0);
        /* one less nonvolatile object for this object's owner */
        vm_purgeable_nonvolatile_owner_update(object->vo_purgeable_owner, -1);

        if (queue->type == PURGEABLE_Q_TYPE_OBSOLETE)
                group = 0;

        if (queue->type != PURGEABLE_Q_TYPE_LIFO)       /* fifo and obsolete are
                                                         * fifo-queued */
                queue_enter(&queue->objq[group], object, vm_object_t, objq);    /* last to die */
        else
                queue_enter_first(&queue->objq[group], object, vm_object_t, objq);      /* first to die */
        /* one more volatile object for this object's owner */
        vm_purgeable_volatile_owner_update(object->vo_purgeable_owner, +1);

        object->purgeable_queue_type = queue->type;
        object->purgeable_queue_group = group;

#if DEBUG
        assert(object->vo_purgeable_volatilizer == NULL);
        object->vo_purgeable_volatilizer = current_task();
        OSBacktrace(&object->purgeable_volatilizer_bt[0], 16);
#endif /* DEBUG */

#if MACH_ASSERT
        queue->debug_count_objects++;
        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_ADD)),
                              0,
                              tokens[queue->token_q_head].count,
                              queue->type,
                              group,
                              0);
#endif

        lck_mtx_unlock(&vm_purgeable_queue_lock);
}

/* Look for object. If found, remove from purgeable queue. */
/* Called with object lock held */
purgeable_q_t
vm_purgeable_object_remove(vm_object_t object)
{
        int group;
        enum purgeable_q_type type;
        purgeable_q_t queue;

        vm_object_lock_assert_exclusive(object);

        type = object->purgeable_queue_type;
        group = object->purgeable_queue_group;

        if (type == PURGEABLE_Q_TYPE_MAX) {
                if (object->objq.prev || object->objq.next)
                        panic("unmarked object on purgeable q");

                return NULL;
        } else if (!(object->objq.prev && object->objq.next))
                panic("marked object not on purgeable q");

        lck_mtx_lock(&vm_purgeable_queue_lock);

        queue = &purgeable_queues[type];

        queue_remove(&queue->objq[group], object, vm_object_t, objq);
        object->objq.next = NULL;
        object->objq.prev = NULL;
        /* one less volatile object for this object's owner */
        vm_purgeable_volatile_owner_update(object->vo_purgeable_owner, -1);
#if DEBUG
        object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */
        /* keep queue of non-volatile objects */
        if (object->alive && !object->terminating) {
                task_t  owner;
                queue_enter(&purgeable_nonvolatile_queue, object,
                            vm_object_t, objq);
                assert(purgeable_nonvolatile_count >= 0);
                purgeable_nonvolatile_count++;
                assert(purgeable_nonvolatile_count > 0);
                /* one more nonvolatile object for this object's owner */
                owner = object->vo_purgeable_owner;
                vm_purgeable_nonvolatile_owner_update(owner, +1);
        }

#if MACH_ASSERT
        queue->debug_count_objects--;
        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_REMOVE)),
                              0,
                              tokens[queue->token_q_head].count,
                              queue->type,
                              group,
                              0);
#endif

        lck_mtx_unlock(&vm_purgeable_queue_lock);

        object->purgeable_queue_type = PURGEABLE_Q_TYPE_MAX;
        object->purgeable_queue_group = 0;

        vm_object_lock_assert_exclusive(object);

        return &purgeable_queues[type];
}

void
vm_purgeable_stats_helper(vm_purgeable_stat_t *stat, purgeable_q_t queue, int group, task_t target_task)
{
        lck_mtx_assert(&vm_purgeable_queue_lock, LCK_MTX_ASSERT_OWNED);

        stat->count = stat->size = 0;
        vm_object_t     object;
        for (object = (vm_object_t) queue_first(&queue->objq[group]);
             !queue_end(&queue->objq[group], (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq)) {
                        if (!target_task || object->vo_purgeable_owner == target_task) {
                                stat->count++;
                                stat->size += (object->resident_page_count * PAGE_SIZE);
                        }
        }
        return;
}

void
vm_purgeable_stats(vm_purgeable_info_t info, task_t target_task)
{
        purgeable_q_t   queue;
        int             group;

        lck_mtx_lock(&vm_purgeable_queue_lock);
        
        /* Populate fifo_data */
        queue = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++)
                vm_purgeable_stats_helper(&(info->fifo_data[group]), queue, group, target_task);
        
        /* Populate lifo_data */
        queue = &purgeable_queues[PURGEABLE_Q_TYPE_LIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++)
                vm_purgeable_stats_helper(&(info->lifo_data[group]), queue, group, target_task);

        /* Populate obsolete data */
        queue = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
        vm_purgeable_stats_helper(&(info->obsolete_data), queue, 0, target_task);

        lck_mtx_unlock(&vm_purgeable_queue_lock);
        return;
}

#if DEVELOPMENT || DEBUG
static void
vm_purgeable_account_volatile_queue(
        purgeable_q_t queue,
        int group,
        task_t task,
        pvm_account_info_t acnt_info)
{
        vm_object_t object;
        uint64_t compressed_count;

        for (object = (vm_object_t) queue_first(&queue->objq[group]);
            !queue_end(&queue->objq[group], (queue_entry_t) object);
            object = (vm_object_t) queue_next(&object->objq)) {
                if (object->vo_purgeable_owner == task) {
                        compressed_count = vm_compressor_pager_get_count(object->pager);
                        acnt_info->pvm_volatile_compressed_count += compressed_count;
                        acnt_info->pvm_volatile_count += (object->resident_page_count - object->wired_page_count);
                        acnt_info->pvm_nonvolatile_count += object->wired_page_count;
                }
        }

}

/*
 * Walks the purgeable object queues and calculates the usage
 * associated with the objects for the given task.
 */
kern_return_t
vm_purgeable_account(
        task_t                  task,
        pvm_account_info_t      acnt_info)
{
        queue_head_t    *nonvolatile_q;
        vm_object_t     object;
        int             group;
        int             state;
        uint64_t        compressed_count;
        purgeable_q_t   volatile_q;


        if ((task == NULL) || (acnt_info == NULL)) {
                return KERN_INVALID_ARGUMENT;
        }

        acnt_info->pvm_volatile_count = 0;
        acnt_info->pvm_volatile_compressed_count = 0;
        acnt_info->pvm_nonvolatile_count = 0;
        acnt_info->pvm_nonvolatile_compressed_count = 0;

        lck_mtx_lock(&vm_purgeable_queue_lock);

        nonvolatile_q = &purgeable_nonvolatile_queue;
        for (object = (vm_object_t) queue_first(nonvolatile_q);
             !queue_end(nonvolatile_q, (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq)) {
                if (object->vo_purgeable_owner == task) {
                        state = object->purgable;
                        compressed_count =  vm_compressor_pager_get_count(object->pager);
                        if (state == VM_PURGABLE_EMPTY) {
                                acnt_info->pvm_volatile_count += (object->resident_page_count - object->wired_page_count);
                                acnt_info->pvm_volatile_compressed_count += compressed_count;
                        } else {
                                acnt_info->pvm_nonvolatile_count += (object->resident_page_count - object->wired_page_count);
                                acnt_info->pvm_nonvolatile_compressed_count += compressed_count;
                        }
                        acnt_info->pvm_nonvolatile_count += object->wired_page_count;
                }
        }

        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
        vm_purgeable_account_volatile_queue(volatile_q, 0, task, acnt_info);

        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                vm_purgeable_account_volatile_queue(volatile_q, group, task, acnt_info);
        }

        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_LIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                vm_purgeable_account_volatile_queue(volatile_q, group, task, acnt_info);
        }
        lck_mtx_unlock(&vm_purgeable_queue_lock);

        acnt_info->pvm_volatile_count = (acnt_info->pvm_volatile_count * PAGE_SIZE);
        acnt_info->pvm_volatile_compressed_count = (acnt_info->pvm_volatile_compressed_count * PAGE_SIZE);
        acnt_info->pvm_nonvolatile_count = (acnt_info->pvm_nonvolatile_count * PAGE_SIZE);
        acnt_info->pvm_nonvolatile_compressed_count = (acnt_info->pvm_nonvolatile_compressed_count * PAGE_SIZE);

        return KERN_SUCCESS;
}
#endif /* DEVELOPMENT || DEBUG */

static void
vm_purgeable_volatile_queue_disown(
        purgeable_q_t   queue,
        int             group,
        task_t          task)
{
        vm_object_t     object;
        int             collisions;

        collisions = 0;

again:
        lck_mtx_assert(&vm_purgeable_queue_lock, LCK_MTX_ASSERT_OWNED);

        for (object = (vm_object_t) queue_first(&queue->objq[group]);
             !queue_end(&queue->objq[group], (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq)) {
#if MACH_ASSERT
                /*
                 * Sanity check: let's scan the entire queues to
                 * make sure we don't leave any purgeable objects
                 * pointing back at a dead task.  If the counters
                 * are off, we would fail to assert that they go
                 * back to 0 after disowning is done.
                 */
#else /* MACH_ASSERT */
                if (task->task_volatile_objects == 0) {
                        /* no more volatile objects owned by "task" */
                        break;
                }
#endif /* MACH_ASSERT */
                if (object->vo_purgeable_owner == task) {
                        if (! vm_object_lock_try(object)) {
                                lck_mtx_unlock(&vm_purgeable_queue_lock);
                                mutex_pause(collisions++);
                                lck_mtx_lock(&vm_purgeable_queue_lock);
                                goto again;
                        }
                        assert(object->purgable == VM_PURGABLE_VOLATILE);
                        if (object->vo_purgeable_owner == task) {
                                vm_purgeable_accounting(object,
                                                        object->purgable,
                                                        TRUE); /* disown */
                                assert(object->vo_purgeable_owner == NULL);
                        }
                        vm_object_unlock(object);
                }
        }
}

void
vm_purgeable_disown(
        task_t  task)
{
        purgeable_q_t   volatile_q;
        int             group;
        queue_head_t    *nonvolatile_q;
        vm_object_t     object;
        int             collisions;

        if (task == NULL) {
                return;
        }

        task->task_purgeable_disowning = TRUE;

        /*
         * Scan the purgeable objects queues for objects owned by "task".
         * This has to be done "atomically" under the "vm_purgeable_queue"
         * lock, to ensure that no new purgeable object get associated
         * with this task or moved between queues while we're scanning.
         */

        /*
         * Scan non-volatile queue for objects owned by "task".
         */

        collisions = 0;

again:
        if (task->task_purgeable_disowned) {
                /* task has already disowned its purgeable memory */
                assert(task->task_volatile_objects == 0);
                assert(task->task_nonvolatile_objects == 0);
                return;
        }
        lck_mtx_lock(&vm_purgeable_queue_lock);

        nonvolatile_q = &purgeable_nonvolatile_queue;
        for (object = (vm_object_t) queue_first(nonvolatile_q);
              !queue_end(nonvolatile_q, (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq)) {
#if MACH_ASSERT
                /*
                 * Sanity check: let's scan the entire queues to
                 * make sure we don't leave any purgeable objects
                 * pointing back at a dead task.  If the counters
                 * are off, we would fail to assert that they go
                 * back to 0 after disowning is done.
                 */
#else /* MACH_ASSERT */
                if (task->task_nonvolatile_objects == 0) {
                        /* no more non-volatile objects owned by "task" */
                        break;
                }
#endif /* MACH_ASSERT */
#if DEBUG
                assert(object->vo_purgeable_volatilizer == NULL);
#endif /* DEBUG */
                if (object->vo_purgeable_owner == task) {
                        if (!vm_object_lock_try(object)) {
                                lck_mtx_unlock(&vm_purgeable_queue_lock);
                                mutex_pause(collisions++);
                                goto again;
                        }
                        if (object->vo_purgeable_owner == task) {
                                vm_purgeable_accounting(object,
                                                        object->purgable,
                                                        TRUE); /* disown */
                                assert(object->vo_purgeable_owner == NULL);
                        }
                        vm_object_unlock(object);
                }
        }

        lck_mtx_yield(&vm_purgeable_queue_lock);

        /*
         * Scan volatile queues for objects owned by "task".
         */

        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
        vm_purgeable_volatile_queue_disown(volatile_q, 0, task);
        lck_mtx_yield(&vm_purgeable_queue_lock);

        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                vm_purgeable_volatile_queue_disown(volatile_q, group, task);
                lck_mtx_yield(&vm_purgeable_queue_lock);
        }
        
        volatile_q = &purgeable_queues[PURGEABLE_Q_TYPE_LIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++) {
                vm_purgeable_volatile_queue_disown(volatile_q, group, task);
                lck_mtx_yield(&vm_purgeable_queue_lock);
        }

        if (task->task_volatile_objects != 0 ||
            task->task_nonvolatile_objects != 0) {
                /* some purgeable objects sneaked into a queue: find them */
                lck_mtx_unlock(&vm_purgeable_queue_lock);
                mutex_pause(collisions++);
                goto again;
        }

        /* there shouldn't be any purgeable objects owned by task now */
        assert(task->task_volatile_objects == 0);
        assert(task->task_nonvolatile_objects == 0);
        assert(task->task_purgeable_disowning);

        /* and we don't need to try and disown again */
        task->task_purgeable_disowned = TRUE;

        lck_mtx_unlock(&vm_purgeable_queue_lock);
}


#if notyet
static int
vm_purgeable_queue_purge_task_owned(
        purgeable_q_t   queue,
        int             group,
        task_t          task)
{
        vm_object_t     object;
        int             num_objects;
        int             collisions;
        int             num_objects_purged;

        num_objects_purged = 0;
        collisions = 0;

look_again:
        lck_mtx_lock(&vm_purgeable_queue_lock);

        num_objects = 0;
        for (object = (vm_object_t) queue_first(&queue->objq[group]);
             !queue_end(&queue->objq[group], (queue_entry_t) object);
             object = (vm_object_t) queue_next(&object->objq)) {

                if (object->vo_purgeable_owner != task &&
                    object->vo_purgeable_owner != NULL) {
                        continue;
                }

                /* found an object: try and grab it */
                if (!vm_object_lock_try(object)) {
                        lck_mtx_unlock(&vm_purgeable_queue_lock);
                        mutex_pause(collisions++);
                        goto look_again;
                }
                /* got it ! */

                collisions = 0;

                /* remove object from purgeable queue */
                queue_remove(&queue->objq[group], object,
                             vm_object_t, objq);
                object->objq.next = NULL;
                object->objq.prev = NULL;
                /* one less volatile object for this object's owner */
                assert(object->vo_purgeable_owner == task);
                vm_purgeable_volatile_owner_update(task, -1);

#if DEBUG
                object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */
                queue_enter(&purgeable_nonvolatile_queue, object,
                            vm_object_t, objq);
                assert(purgeable_nonvolatile_count >= 0);
                purgeable_nonvolatile_count++;
                assert(purgeable_nonvolatile_count > 0);
                /* one more nonvolatile object for this object's owner */
                assert(object->vo_purgeable_owner == task);
                vm_purgeable_nonvolatile_owner_update(task, +1);

                /* unlock purgeable queues */
                lck_mtx_unlock(&vm_purgeable_queue_lock);

                if (object->purgeable_when_ripe) {
                        /* remove a token */
                        vm_page_lock_queues();
                        vm_purgeable_token_remove_first(queue);
                        vm_page_unlock_queues();
                }

                /* purge the object */
                (void) vm_object_purge(object, 0);
                assert(object->purgable == VM_PURGABLE_EMPTY);
                /* no change for purgeable accounting */
                vm_object_unlock(object);
                num_objects_purged++;

                /* we unlocked the purgeable queues, so start over */
                goto look_again;
        }

        lck_mtx_unlock(&vm_purgeable_queue_lock);

        return num_objects_purged;
}

int
vm_purgeable_purge_task_owned(
        task_t  task)
{
        purgeable_q_t   queue;
        int             group;
        int             num_objects_purged;

        num_objects_purged = 0;

        queue = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
        num_objects_purged += vm_purgeable_queue_purge_task_owned(queue,
                                                                  0,
                                                                  task);

        queue = &purgeable_queues[PURGEABLE_Q_TYPE_FIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++)
                num_objects_purged += vm_purgeable_queue_purge_task_owned(queue,
                                                                          group,
                                                                          task);
        
        queue = &purgeable_queues[PURGEABLE_Q_TYPE_LIFO];
        for (group = 0; group < NUM_VOLATILE_GROUPS; group++)
                num_objects_purged += vm_purgeable_queue_purge_task_owned(queue,
                                                                          group,
                                                                          task);

        return num_objects_purged;
}
#endif

void
vm_purgeable_nonvolatile_enqueue(
        vm_object_t     object,
        task_t          owner)
{
        int page_count;

        vm_object_lock_assert_exclusive(object);

        assert(object->purgable == VM_PURGABLE_NONVOLATILE);
        assert(object->vo_purgeable_owner == NULL);
        assert(owner != NULL);

        lck_mtx_lock(&vm_purgeable_queue_lock);

        if (owner->task_purgeable_disowning) {
                /* task is exiting and no longer tracking purgeable objects */
                owner = NULL;
        }

        object->vo_purgeable_owner = owner;
#if DEBUG
        object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */

#if DEBUG
        OSBacktrace(&object->purgeable_owner_bt[0], 16);
#endif /* DEBUG */

        page_count = object->resident_page_count;
        assert(page_count == 0); /* should be a freshly-created object */
        if (owner != NULL && page_count != 0) {
                ledger_credit(owner->ledger,
                              task_ledgers.purgeable_nonvolatile,
                              ptoa(page_count));
                ledger_credit(owner->ledger,
                              task_ledgers.phys_footprint,
                              ptoa(page_count));
        }
                      
        assert(object->objq.next == NULL);
        assert(object->objq.prev == NULL);

        queue_enter(&purgeable_nonvolatile_queue, object,
                    vm_object_t, objq);
        assert(purgeable_nonvolatile_count >= 0);
        purgeable_nonvolatile_count++;
        assert(purgeable_nonvolatile_count > 0);
        /* one more nonvolatile object for this object's owner */
        assert(object->vo_purgeable_owner == owner);
        vm_purgeable_nonvolatile_owner_update(owner, +1);
        lck_mtx_unlock(&vm_purgeable_queue_lock);

        vm_object_lock_assert_exclusive(object);
}

void
vm_purgeable_nonvolatile_dequeue(
        vm_object_t     object)
{
        task_t  owner;

        vm_object_lock_assert_exclusive(object);

        owner = object->vo_purgeable_owner;
#if DEBUG
        assert(object->vo_purgeable_volatilizer == NULL);
#endif /* DEBUG */
        if (owner != NULL) {
                /*
                 * Update the owner's ledger to stop accounting
                 * for this object.
                 */
                vm_purgeable_accounting(object,
                                        object->purgable,
                                        TRUE); /* disown */
        }

        lck_mtx_lock(&vm_purgeable_queue_lock);
        assert(object->objq.next != NULL);
        assert(object->objq.prev != NULL);
        queue_remove(&purgeable_nonvolatile_queue, object,
                     vm_object_t, objq);
        object->objq.next = NULL;
        object->objq.prev = NULL;
        assert(purgeable_nonvolatile_count > 0);
        purgeable_nonvolatile_count--;
        assert(purgeable_nonvolatile_count >= 0);
        lck_mtx_unlock(&vm_purgeable_queue_lock);

        vm_object_lock_assert_exclusive(object);
}

void
vm_purgeable_accounting(
        vm_object_t     object,
        vm_purgable_t   old_state,
        boolean_t       disown)
{
        task_t          owner;
        int             resident_page_count;
        int             wired_page_count;
        int             compressed_page_count;
        boolean_t       disown_on_the_fly;

        vm_object_lock_assert_exclusive(object);

        owner = object->vo_purgeable_owner;
        if (owner == NULL)
                return;

        if (!disown && owner->task_purgeable_disowning) {
                /* task is disowning its purgeable objects: help it */
                disown_on_the_fly = TRUE;
        } else {
                disown_on_the_fly = FALSE;
        }

        resident_page_count = object->resident_page_count;
        wired_page_count = object->wired_page_count;
        if ((COMPRESSED_PAGER_IS_ACTIVE ||
             DEFAULT_FREEZER_COMPRESSED_PAGER_IS_ACTIVE) &&
            object->pager != NULL) {
                compressed_page_count =
                        vm_compressor_pager_get_count(object->pager);
        } else {
                compressed_page_count = 0;
        }

        if (old_state == VM_PURGABLE_VOLATILE ||
            old_state == VM_PURGABLE_EMPTY) {
                /* less volatile bytes in ledger */
                ledger_debit(owner->ledger,
                             task_ledgers.purgeable_volatile,
                             ptoa(resident_page_count - wired_page_count));
                /* less compressed volatile bytes in ledger */
                ledger_debit(owner->ledger,
                             task_ledgers.purgeable_volatile_compressed,
                             ptoa(compressed_page_count));

                if (disown || !object->alive || object->terminating) {
                        /* wired pages were accounted as "non-volatile"... */
                        ledger_debit(owner->ledger,
                                     task_ledgers.purgeable_nonvolatile,
                                     ptoa(wired_page_count));
                        /* ... and in phys_footprint */
                        ledger_debit(owner->ledger,
                                     task_ledgers.phys_footprint,
                                     ptoa(wired_page_count));

                        if (!disown_on_the_fly &&
                            (object->purgeable_queue_type ==
                             PURGEABLE_Q_TYPE_MAX)) {
                                /*
                                 * Not on a volatile queue:  must be empty
                                 * or emptying.
                                 */
                                vm_purgeable_nonvolatile_owner_update(owner,-1);
                        } else {
                                /* on a volatile queue */
                                vm_purgeable_volatile_owner_update(owner, -1);
                        }
                        /* no more accounting for this dead object */
                        object->vo_purgeable_owner = NULL;
#if DEBUG
                        object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */
                        return;
                }

                /* more non-volatile bytes in ledger */
                ledger_credit(owner->ledger,
                              task_ledgers.purgeable_nonvolatile,
                              ptoa(resident_page_count - wired_page_count));
                /* more compressed non-volatile bytes in ledger */
                ledger_credit(owner->ledger,
                              task_ledgers.purgeable_nonvolatile_compressed,
                              ptoa(compressed_page_count));
                /* more footprint */
                ledger_credit(owner->ledger,
                              task_ledgers.phys_footprint,
                              ptoa(resident_page_count
                                   + compressed_page_count
                                   - wired_page_count));

        } else if (old_state == VM_PURGABLE_NONVOLATILE) {

                /* less non-volatile bytes in ledger */
                ledger_debit(owner->ledger,
                             task_ledgers.purgeable_nonvolatile,
                             ptoa(resident_page_count - wired_page_count));
                /* less compressed non-volatile bytes in ledger */
                ledger_debit(owner->ledger,
                             task_ledgers.purgeable_nonvolatile_compressed,
                             ptoa(compressed_page_count));
                /* less footprint */
                ledger_debit(owner->ledger,
                             task_ledgers.phys_footprint,
                             ptoa(resident_page_count
                                  + compressed_page_count
                                  - wired_page_count));

                if (disown || !object->alive || object->terminating) {
                        /* wired pages still accounted as "non-volatile" */
                        ledger_debit(owner->ledger,
                                     task_ledgers.purgeable_nonvolatile,
                                     ptoa(wired_page_count));
                        ledger_debit(owner->ledger,
                                     task_ledgers.phys_footprint,
                                     ptoa(wired_page_count));

                        /* one less "non-volatile" object for the owner */
                        if (!disown_on_the_fly) {
                                assert(object->purgeable_queue_type ==
                                       PURGEABLE_Q_TYPE_MAX);
                        }
                        vm_purgeable_nonvolatile_owner_update(owner, -1);
                        /* no more accounting for this dead object */
                        object->vo_purgeable_owner = NULL;
#if DEBUG
                        object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */
                        return;
                }
                /* more volatile bytes in ledger */
                ledger_credit(owner->ledger,
                              task_ledgers.purgeable_volatile,
                              ptoa(resident_page_count - wired_page_count));
                /* more compressed volatile bytes in ledger */
                ledger_credit(owner->ledger,
                              task_ledgers.purgeable_volatile_compressed,
                              ptoa(compressed_page_count));
        } else {
                panic("vm_purgeable_accounting(%p): "
                      "unexpected old_state=%d\n",
                      object, old_state);
        }

        vm_object_lock_assert_exclusive(object);
}

void
vm_purgeable_nonvolatile_owner_update(
        task_t  owner,
        int     delta)
{
        if (owner == NULL || delta == 0) {
                return;
        }

        if (delta > 0) {
                assert(owner->task_nonvolatile_objects >= 0);
                OSAddAtomic(delta, &owner->task_nonvolatile_objects);
                assert(owner->task_nonvolatile_objects > 0);
        } else {
                assert(owner->task_nonvolatile_objects > delta);
                OSAddAtomic(delta, &owner->task_nonvolatile_objects);
                assert(owner->task_nonvolatile_objects >= 0);
        }
}

void
vm_purgeable_volatile_owner_update(
        task_t  owner,
        int     delta)
{
        if (owner == NULL || delta == 0) {
                return;
        }

        if (delta > 0) {
                assert(owner->task_volatile_objects >= 0);
                OSAddAtomic(delta, &owner->task_volatile_objects);
                assert(owner->task_volatile_objects > 0);
        } else {
                assert(owner->task_volatile_objects > delta);
                OSAddAtomic(delta, &owner->task_volatile_objects);
                assert(owner->task_volatile_objects >= 0);
        }
}

void
vm_purgeable_compressed_update(
        vm_object_t     object,
        int             delta)
{
        task_t  owner;

        vm_object_lock_assert_exclusive(object);

        if (delta == 0 ||
            !object->internal ||
            object->purgable == VM_PURGABLE_DENY ||
            object->vo_purgeable_owner == NULL) {
                /* not an owned purgeable VM object: nothing to update */
                return;
        }
        
        owner = object->vo_purgeable_owner;
        switch (object->purgable) {
        case VM_PURGABLE_DENY:
                break;
        case VM_PURGABLE_NONVOLATILE:
                if (delta > 0) {
                        ledger_credit(owner->ledger,
                                      task_ledgers.purgeable_nonvolatile_compressed,
                                      ptoa(delta));
                        ledger_credit(owner->ledger,
                                      task_ledgers.phys_footprint,
                                      ptoa(delta));
                } else {
                        ledger_debit(owner->ledger,
                                     task_ledgers.purgeable_nonvolatile_compressed,
                                     ptoa(-delta));
                        ledger_debit(owner->ledger,
                                     task_ledgers.phys_footprint,
                                     ptoa(-delta));
                }
                break;
        case VM_PURGABLE_VOLATILE:
        case VM_PURGABLE_EMPTY:
                if (delta > 0) {
                        ledger_credit(owner->ledger,
                                      task_ledgers.purgeable_volatile_compressed,
                                      ptoa(delta));
                } else {
                        ledger_debit(owner->ledger,
                                     task_ledgers.purgeable_volatile_compressed,
                                     ptoa(-delta));
                }
                break;
        default:
                panic("vm_purgeable_compressed_update(): "
                      "unexpected purgable %d for object %p\n",
                      object->purgable, object);
        }
}