vm_purgeable.c   [plain text]

/*
 * 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 <kern/policy_internal.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>

/*
 * LOCK ORDERING for task-owned purgeable objects
 *
 * Whenever we need to hold multiple locks while adding to, removing from,
 * or scanning a task's task_objq list of VM objects it owns, locks should
 * be taken in this order:
 *
 * VM object ==> vm_purgeable_queue_lock ==> owner_task->task_objq_lock
 *
 * If one needs to acquire the VM object lock after any of the other 2 locks,
 * one needs to use vm_object_lock_try() and, if that fails, release the
 * other locks and retake them all in the correct order.
 */

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);


#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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);

	/* 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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);

	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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);

	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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
	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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
	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()
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);

	/* 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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
	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)
{
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
	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;

		/*
		 * We don't want to use VM_OBJECT_OWNER() here: we want to
		 * distinguish kernel-owned and disowned objects.
		 * Disowned objects have no owner and will have no importance...
		 */
		owner = object->vo_owner;
		if (owner != NULL && owner != VM_OBJECT_OWNER_DISOWNED) {
#if CONFIG_EMBEDDED
#if CONFIG_JETSAM
			object_task_importance = proc_get_memstat_priority((struct proc *)get_bsdtask_info(owner), TRUE);
#endif /* CONFIG_JETSAM */
#else /* CONFIG_EMBEDDED */
			object_task_importance = task_importance_estimate(owner);
#endif /* CONFIG_EMBEDDED */
		}

		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(VM_OBJECT_OWNER(object), -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(VM_OBJECT_OWNER(object), +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;
	unsigned int    resident_page_count;


	KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE)) | DBG_FUNC_START,
	    force_purge_below_group, flags, 0, 0, 0);

	/* Need the page queue lock since we'll be changing the token queue. */
	LCK_MTX_ASSERT(&vm_page_queue_lock, LCK_MTX_ASSERT_OWNED);
	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);

	KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE)) | DBG_FUNC_END,
	    0, 0, available_for_purge, 0, 0);

	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_owner, task_importance_estimate(object->vo_owner), i, group, force_purge_below_group, memorystatus_vm_pressure_level);
	resident_page_count = object->resident_page_count;
	(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();

	vm_pageout_vminfo.vm_pageout_pages_purged += resident_page_count;

	KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, OBJECT_PURGE)) | DBG_FUNC_END,
	    VM_KERNEL_UNSLIDE_OR_PERM(object),                          /* purged object */
	    resident_page_count,
	    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(VM_OBJECT_OWNER(object), -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(VM_OBJECT_OWNER(object), +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],
	    ARRAY_COUNT(object->purgeable_volatilizer_bt));
#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(VM_OBJECT_OWNER(object), -1);
#if DEBUG
	object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */
	/* keep queue of non-volatile objects */
	if (object->alive && !object->terminating) {
		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(VM_OBJECT_OWNER(object), +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 || VM_OBJECT_OWNER(object) == 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 (VM_OBJECT_OWNER(object) == 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 (VM_OBJECT_OWNER(object) == 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 */

void
vm_purgeable_disown(
	task_t  task)
{
	vm_object_t     next_object;
	vm_object_t     object;
	int             collisions;

	if (task == NULL) {
		return;
	}

	/*
	 * 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);
	task_objq_lock(task);

	task->task_purgeable_disowning = TRUE;

	for (object = (vm_object_t) queue_first(&task->task_objq);
	    !queue_end(&task->task_objq, (queue_entry_t) object);
	    object = next_object) {
		if (task->task_nonvolatile_objects == 0 &&
		    task->task_volatile_objects == 0) {
			/* no more purgeable objects owned by "task" */
			break;
		}

		next_object = (vm_object_t) queue_next(&object->task_objq);
		if (object->purgable == VM_PURGABLE_DENY) {
			/* not a purgeable object: skip */
			continue;
		}

#if DEBUG
		assert(object->vo_purgeable_volatilizer == NULL);
#endif /* DEBUG */
		assert(object->vo_owner == task);
		if (!vm_object_lock_try(object)) {
			lck_mtx_unlock(&vm_purgeable_queue_lock);
			task_objq_unlock(task);
			mutex_pause(collisions++);
			goto again;
		}
		/* transfer ownership to the kernel */
		assert(VM_OBJECT_OWNER(object) != kernel_task);
		vm_object_ownership_change(
			object,
			object->vo_ledger_tag, /* unchanged */
			VM_OBJECT_OWNER_DISOWNED, /* new owner */
			TRUE);  /* old_owner->task_objq locked */
		assert(object->vo_owner == VM_OBJECT_OWNER_DISOWNED);
		vm_object_unlock(object);
	}

	if (__improbable(task->task_volatile_objects != 0 ||
	    task->task_nonvolatile_objects != 0)) {
		panic("%s(%p): volatile=%d nonvolatile=%d q=%p q_first=%p q_last=%p",
		    __FUNCTION__,
		    task,
		    task->task_volatile_objects,
		    task->task_nonvolatile_objects,
		    &task->task_objq,
		    queue_first(&task->task_objq),
		    queue_last(&task->task_objq));
	}

	/* 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);
	task_objq_unlock(task);
}


static uint64_t
vm_purgeable_queue_purge_task_owned(
	purgeable_q_t   queue,
	int             group,
	task_t          task)
{
	vm_object_t     object = VM_OBJECT_NULL;
	int             collisions = 0;
	uint64_t        num_pages_purged = 0;

	num_pages_purged = 0;
	collisions = 0;

look_again:
	lck_mtx_lock(&vm_purgeable_queue_lock);

	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_owner != task) {
			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;
		object->purgeable_queue_type = PURGEABLE_Q_TYPE_MAX;
		object->purgeable_queue_group = 0;
		/* one less volatile object for this object's owner */
		assert(object->vo_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_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 */
		num_pages_purged += vm_object_purge(object, 0);

		assert(object->purgable == VM_PURGABLE_EMPTY);
		/* no change for purgeable accounting */
		vm_object_unlock(object);

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

	lck_mtx_unlock(&vm_purgeable_queue_lock);

	return num_pages_purged;
}

uint64_t
vm_purgeable_purge_task_owned(
	task_t  task)
{
	purgeable_q_t   queue = NULL;
	int             group = 0;
	uint64_t        num_pages_purged = 0;

	num_pages_purged = 0;

	queue = &purgeable_queues[PURGEABLE_Q_TYPE_OBSOLETE];
	num_pages_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_pages_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_pages_purged += vm_purgeable_queue_purge_task_owned(queue,
		    group,
		    task);
	}

	return num_pages_purged;
}

void
vm_purgeable_nonvolatile_enqueue(
	vm_object_t     object,
	task_t          owner)
{
	vm_object_lock_assert_exclusive(object);

	assert(object->purgable == VM_PURGABLE_NONVOLATILE);
	assert(object->vo_owner == NULL);

	lck_mtx_lock(&vm_purgeable_queue_lock);

	if (owner != NULL &&
	    owner->task_purgeable_disowning) {
		/* task is exiting and no longer tracking purgeable objects */
		owner = VM_OBJECT_OWNER_DISOWNED;
	}
	if (owner == NULL) {
		owner = kernel_task;
	}
#if DEBUG
	OSBacktrace(&object->purgeable_owner_bt[0],
	    ARRAY_COUNT(object->purgeable_owner_bt));
	object->vo_purgeable_volatilizer = NULL;
#endif /* DEBUG */

	vm_object_ownership_change(object,
	    object->vo_ledger_tag,                        /* tag unchanged */
	    owner,
	    FALSE);                             /* task_objq_locked */

	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);
	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 = VM_OBJECT_OWNER(object);
#if DEBUG
	assert(object->vo_purgeable_volatilizer == NULL);
#endif /* DEBUG */
	if (owner != NULL) {
		/*
		 * Update the owner's ledger to stop accounting
		 * for this object.
		 */
		/* transfer ownership to the kernel */
		assert(VM_OBJECT_OWNER(object) != kernel_task);
		vm_object_ownership_change(
			object,
			object->vo_ledger_tag,  /* unchanged */
			VM_OBJECT_OWNER_DISOWNED, /* new owner */
			FALSE); /* old_owner->task_objq locked */
		assert(object->vo_owner == VM_OBJECT_OWNER_DISOWNED);
	}

	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)
{
	task_t          owner;
	int             resident_page_count;
	int             wired_page_count;
	int             compressed_page_count;
	int             ledger_idx_volatile;
	int             ledger_idx_nonvolatile;
	int             ledger_idx_volatile_compressed;
	int             ledger_idx_nonvolatile_compressed;
	boolean_t       do_footprint;

	vm_object_lock_assert_exclusive(object);
	assert(object->purgable != VM_PURGABLE_DENY);

	owner = VM_OBJECT_OWNER(object);
	if (owner == NULL ||
	    object->purgable == VM_PURGABLE_DENY) {
		return;
	}

	vm_object_ledger_tag_ledgers(object,
	    &ledger_idx_volatile,
	    &ledger_idx_nonvolatile,
	    &ledger_idx_volatile_compressed,
	    &ledger_idx_nonvolatile_compressed,
	    &do_footprint);

	resident_page_count = object->resident_page_count;
	wired_page_count = object->wired_page_count;
	if (VM_CONFIG_COMPRESSOR_IS_PRESENT &&
	    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,
		    ledger_idx_volatile,
		    ptoa_64(resident_page_count - wired_page_count));
		/* less compressed volatile bytes in ledger */
		ledger_debit(owner->ledger,
		    ledger_idx_volatile_compressed,
		    ptoa_64(compressed_page_count));

		/* more non-volatile bytes in ledger */
		ledger_credit(owner->ledger,
		    ledger_idx_nonvolatile,
		    ptoa_64(resident_page_count - wired_page_count));
		/* more compressed non-volatile bytes in ledger */
		ledger_credit(owner->ledger,
		    ledger_idx_nonvolatile_compressed,
		    ptoa_64(compressed_page_count));
		if (do_footprint) {
			/* more footprint */
			ledger_credit(owner->ledger,
			    task_ledgers.phys_footprint,
			    ptoa_64(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,
		    ledger_idx_nonvolatile,
		    ptoa_64(resident_page_count - wired_page_count));
		/* less compressed non-volatile bytes in ledger */
		ledger_debit(owner->ledger,
		    ledger_idx_nonvolatile_compressed,
		    ptoa_64(compressed_page_count));
		if (do_footprint) {
			/* less footprint */
			ledger_debit(owner->ledger,
			    task_ledgers.phys_footprint,
			    ptoa_64(resident_page_count
			    + compressed_page_count
			    - wired_page_count));
		}

		/* more volatile bytes in ledger */
		ledger_credit(owner->ledger,
		    ledger_idx_volatile,
		    ptoa_64(resident_page_count - wired_page_count));
		/* more compressed volatile bytes in ledger */
		ledger_credit(owner->ledger,
		    ledger_idx_volatile_compressed,
		    ptoa_64(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_object_owner_compressed_update(
	vm_object_t     object,
	int             delta)
{
	task_t          owner;
	int             ledger_idx_volatile;
	int             ledger_idx_nonvolatile;
	int             ledger_idx_volatile_compressed;
	int             ledger_idx_nonvolatile_compressed;
	boolean_t       do_footprint;

	vm_object_lock_assert_exclusive(object);

	owner = VM_OBJECT_OWNER(object);

	if (delta == 0 ||
	    !object->internal ||
	    (object->purgable == VM_PURGABLE_DENY &&
	    !object->vo_ledger_tag) ||
	    owner == NULL) {
		/* not an owned purgeable (or tagged) VM object: nothing to update */
		return;
	}

	vm_object_ledger_tag_ledgers(object,
	    &ledger_idx_volatile,
	    &ledger_idx_nonvolatile,
	    &ledger_idx_volatile_compressed,
	    &ledger_idx_nonvolatile_compressed,
	    &do_footprint);
	switch (object->purgable) {
	case VM_PURGABLE_DENY:
		/* not purgeable: must be ledger-tagged */
		assert(object->vo_ledger_tag != VM_OBJECT_LEDGER_TAG_NONE);
	/* fallthru */
	case VM_PURGABLE_NONVOLATILE:
		if (delta > 0) {
			ledger_credit(owner->ledger,
			    ledger_idx_nonvolatile_compressed,
			    ptoa_64(delta));
			if (do_footprint) {
				ledger_credit(owner->ledger,
				    task_ledgers.phys_footprint,
				    ptoa_64(delta));
			}
		} else {
			ledger_debit(owner->ledger,
			    ledger_idx_nonvolatile_compressed,
			    ptoa_64(-delta));
			if (do_footprint) {
				ledger_debit(owner->ledger,
				    task_ledgers.phys_footprint,
				    ptoa_64(-delta));
			}
		}
		break;
	case VM_PURGABLE_VOLATILE:
	case VM_PURGABLE_EMPTY:
		if (delta > 0) {
			ledger_credit(owner->ledger,
			    ledger_idx_volatile_compressed,
			    ptoa_64(delta));
		} else {
			ledger_debit(owner->ledger,
			    ledger_idx_volatile_compressed,
			    ptoa_64(-delta));
		}
		break;
	default:
		panic("vm_purgeable_compressed_update(): "
		    "unexpected purgable %d for object %p\n",
		    object->purgable, object);
	}
}