xnu-3248.20.55.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);
	}
}