path: root/vm/vm_resident.c

/*
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University.
 * Copyright (c) 1993,1994 The University of Utah and
 * the Computer Systems Laboratory (CSL).
 * All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON, THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF
 * THIS SOFTWARE IN ITS "AS IS" CONDITION, AND DISCLAIM ANY LIABILITY
 * OF ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF
 * THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 *	File:	vm/vm_page.c
 *	Author:	Avadis Tevanian, Jr., Michael Wayne Young
 *
 *	Resident memory management module.
 */

#include <kern/printf.h>
#include <string.h>

#include <mach/vm_prot.h>
#include <kern/counters.h>
#include <kern/debug.h>
#include <kern/sched_prim.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <mach/vm_statistics.h>
#include <machine/vm_param.h>
#include <kern/xpr.h>
#include <kern/slab.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_kern.h>

#if	MACH_VM_DEBUG
#include <mach/kern_return.h>
#include <mach_debug/hash_info.h>
#include <vm/vm_user.h>
#endif

#if	MACH_KDB
#include <ddb/db_output.h>
#endif	/* MACH_KDB */


/*
 *	Associated with eacn page of user-allocatable memory is a
 *	page structure.
 */

/*
 *	These variables record the values returned by vm_page_bootstrap,
 *	for debugging purposes.  The implementation of pmap_steal_memory
 *	and pmap_startup here also uses them internally.
 */

vm_offset_t virtual_space_start;
vm_offset_t virtual_space_end;

/*
 *	The vm_page_lookup() routine, which provides for fast
 *	(virtual memory object, offset) to page lookup, employs
 *	the following hash table.  The vm_page_{insert,remove}
 *	routines install and remove associations in the table.
 *	[This table is often called the virtual-to-physical,
 *	or VP, table.]
 */
typedef struct {
	decl_simple_lock_data(,lock)
	vm_page_t pages;
} vm_page_bucket_t;

vm_page_bucket_t *vm_page_buckets;		/* Array of buckets */
unsigned int	vm_page_bucket_count = 0;	/* How big is array? */
unsigned int	vm_page_hash_mask;		/* Mask for hash function */

/*
 *	Resident page structures are initialized from
 *	a template (see vm_page_alloc).
 *
 *	When adding a new field to the virtual memory
 *	object structure, be sure to add initialization
 *	(see vm_page_bootstrap).
 */
struct vm_page	vm_page_template;

/*
 *	Resident pages that represent real memory
 *	are allocated from a free list.
 */
vm_page_t	vm_page_queue_free;
vm_page_t	vm_page_queue_fictitious;
decl_simple_lock_data(,vm_page_queue_free_lock)
unsigned int	vm_page_free_wanted;
int		vm_page_free_count;
int		vm_page_fictitious_count;
int		vm_page_external_count;

unsigned int	vm_page_free_count_minimum;	/* debugging */

/*
 *	Occasionally, the virtual memory system uses
 *	resident page structures that do not refer to
 *	real pages, for example to leave a page with
 *	important state information in the VP table.
 *
 *	These page structures are allocated the way
 *	most other kernel structures are.
 */
struct kmem_cache	vm_page_cache;

/*
 *	Fictitious pages don't have a physical address,
 *	but we must initialize phys_addr to something.
 *	For debugging, this should be a strange value
 *	that the pmap module can recognize in assertions.
 */
vm_offset_t vm_page_fictitious_addr = (vm_offset_t) -1;

/*
 *	Resident page structures are also chained on
 *	queues that are used by the page replacement
 *	system (pageout daemon).  These queues are
 *	defined here, but are shared by the pageout
 *	module.
 */
queue_head_t	vm_page_queue_active;
queue_head_t	vm_page_queue_inactive;
decl_simple_lock_data(,vm_page_queue_lock)
int	vm_page_active_count;
int	vm_page_inactive_count;
int	vm_page_wire_count;

/*
 *	Several page replacement parameters are also
 *	shared with this module, so that page allocation
 *	(done here in vm_page_alloc) can trigger the
 *	pageout daemon.
 */
int	vm_page_free_target = 0;
int	vm_page_free_min = 0;
int	vm_page_inactive_target = 0;
int	vm_page_free_reserved = 0;
int	vm_page_laundry_count = 0;
int	vm_page_external_limit = 0;


/*
 *	The VM system has a couple of heuristics for deciding
 *	that pages are "uninteresting" and should be placed
 *	on the inactive queue as likely candidates for replacement.
 *	These variables let the heuristics be controlled at run-time
 *	to make experimentation easier.
 */

boolean_t vm_page_deactivate_behind = TRUE;
boolean_t vm_page_deactivate_hint = TRUE;

/*
 *	vm_page_bootstrap:
 *
 *	Initializes the resident memory module.
 *
 *	Allocates memory for the page cells, and
 *	for the object/offset-to-page hash table headers.
 *	Each page cell is initialized and placed on the free list.
 *	Returns the range of available kernel virtual memory.
 */

void vm_page_bootstrap(
	vm_offset_t *startp,
	vm_offset_t *endp)
{
	register vm_page_t m;
	int i;

	/*
	 *	Initialize the vm_page template.
	 */

	m = &vm_page_template;
	m->object = VM_OBJECT_NULL;	/* reset later */
	m->offset = 0;			/* reset later */
	m->wire_count = 0;

	m->inactive = FALSE;
	m->active = FALSE;
	m->laundry = FALSE;
	m->free = FALSE;
	m->external = FALSE;

	m->busy = TRUE;
	m->wanted = FALSE;
	m->tabled = FALSE;
	m->fictitious = FALSE;
	m->private = FALSE;
	m->absent = FALSE;
	m->error = FALSE;
	m->dirty = FALSE;
	m->precious = FALSE;
	m->reference = FALSE;

	m->phys_addr = 0;		/* reset later */

	m->page_lock = VM_PROT_NONE;
	m->unlock_request = VM_PROT_NONE;

	/*
	 *	Initialize the page queues.
	 */

	simple_lock_init(&vm_page_queue_free_lock);
	simple_lock_init(&vm_page_queue_lock);

	vm_page_queue_free = VM_PAGE_NULL;
	vm_page_queue_fictitious = VM_PAGE_NULL;
	queue_init(&vm_page_queue_active);
	queue_init(&vm_page_queue_inactive);

	vm_page_free_wanted = 0;

	/*
	 *	Steal memory for the kernel map entries.
	 */

	kentry_data = pmap_steal_memory(kentry_data_size);

	/*
	 *	Allocate (and initialize) the virtual-to-physical
	 *	table hash buckets.
	 *
	 *	The number of buckets should be a power of two to
	 *	get a good hash function.  The following computation
	 *	chooses the first power of two that is greater
	 *	than the number of physical pages in the system.
	 */

	if (vm_page_bucket_count == 0) {
		unsigned int npages = pmap_free_pages();

		vm_page_bucket_count = 1;
		while (vm_page_bucket_count < npages)
			vm_page_bucket_count <<= 1;
	}

	vm_page_hash_mask = vm_page_bucket_count - 1;

	if (vm_page_hash_mask & vm_page_bucket_count)
		printf("vm_page_bootstrap: WARNING -- strange page hash\n");

	vm_page_buckets = (vm_page_bucket_t *)
		pmap_steal_memory(vm_page_bucket_count *
				  sizeof(vm_page_bucket_t));

	for (i = 0; i < vm_page_bucket_count; i++) {
		register vm_page_bucket_t *bucket = &vm_page_buckets[i];

		bucket->pages = VM_PAGE_NULL;
		simple_lock_init(&bucket->lock);
	}

	/*
	 *	Machine-dependent code allocates the resident page table.
	 *	It uses vm_page_init to initialize the page frames.
	 *	The code also returns to us the virtual space available
	 *	to the kernel.  We don't trust the pmap module
	 *	to get the alignment right.
	 */

	pmap_startup(&virtual_space_start, &virtual_space_end);
	virtual_space_start = round_page(virtual_space_start);
	virtual_space_end = trunc_page(virtual_space_end);

	*startp = virtual_space_start;
	*endp = virtual_space_end;

	/*	printf("vm_page_bootstrap: %d free pages\n", vm_page_free_count);*/
	vm_page_free_count_minimum = vm_page_free_count;
}

#ifndef	MACHINE_PAGES
/*
 *	We implement pmap_steal_memory and pmap_startup with the help
 *	of two simpler functions, pmap_virtual_space and pmap_next_page.
 */

vm_offset_t pmap_steal_memory(
	vm_size_t size)
{
	vm_offset_t addr, vaddr, paddr;

	/*
	 *	We round the size to an integer multiple.
	 */

	size = (size + 3) &~ 3;

	/*
	 *	If this is the first call to pmap_steal_memory,
	 *	we have to initialize ourself.
	 */

	if (virtual_space_start == virtual_space_end) {
		pmap_virtual_space(&virtual_space_start, &virtual_space_end);

		/*
		 *	The initial values must be aligned properly, and
		 *	we don't trust the pmap module to do it right.
		 */

		virtual_space_start = round_page(virtual_space_start);
		virtual_space_end = trunc_page(virtual_space_end);
	}

	/*
	 *	Allocate virtual memory for this request.
	 */

	addr = virtual_space_start;
	virtual_space_start += size;

	/*
	 *	Allocate and map physical pages to back new virtual pages.
	 */

	for (vaddr = round_page(addr);
	     vaddr < addr + size;
	     vaddr += PAGE_SIZE) {
		if (!pmap_next_page(&paddr))
			panic("pmap_steal_memory");

		/*
		 *	XXX Logically, these mappings should be wired,
		 *	but some pmap modules barf if they are.
		 */

		pmap_enter(kernel_pmap, vaddr, paddr,
			   VM_PROT_READ|VM_PROT_WRITE, FALSE);
	}

	return addr;
}

void pmap_startup(
	vm_offset_t *startp,
	vm_offset_t *endp)
{
	unsigned int i, npages, pages_initialized;
	vm_page_t pages;
	vm_offset_t paddr;

	/*
	 *	We calculate how many page frames we will have
	 *	and then allocate the page structures in one chunk.
	 */

	npages = ((PAGE_SIZE * pmap_free_pages() +
		   (round_page(virtual_space_start) - virtual_space_start)) /
		  (PAGE_SIZE + sizeof *pages));

	pages = (vm_page_t) pmap_steal_memory(npages * sizeof *pages);

	/*
	 *	Initialize the page frames.
	 */

	for (i = 0, pages_initialized = 0; i < npages; i++) {
		if (!pmap_next_page(&paddr))
			break;

		vm_page_init(&pages[i], paddr);
		pages_initialized++;
	}
	i = 0;
	while (pmap_next_page(&paddr))
		i++;
	if (i)
		printf("%u memory page(s) left away\n", i);

	/*
	 * Release pages in reverse order so that physical pages
	 * initially get allocated in ascending addresses. This keeps
	 * the devices (which must address physical memory) happy if
	 * they require several consecutive pages.
	 */

	for (i = pages_initialized; i > 0; i--) {
		vm_page_release(&pages[i - 1], FALSE);
	}

	/*
	 *	We have to re-align virtual_space_start,
	 *	because pmap_steal_memory has been using it.
	 */

	virtual_space_start = round_page(virtual_space_start);

	*startp = virtual_space_start;
	*endp = virtual_space_end;
}
#endif	/* MACHINE_PAGES */

/*
 *	Routine:	vm_page_module_init
 *	Purpose:
 *		Second initialization pass, to be done after
 *		the basic VM system is ready.
 */
void		vm_page_module_init(void)
{
	kmem_cache_init(&vm_page_cache, "vm_page", sizeof(struct vm_page), 0,
			NULL, NULL, NULL, 0);
}

/*
 *	Routine:	vm_page_create
 *	Purpose:
 *		After the VM system is up, machine-dependent code
 *		may stumble across more physical memory.  For example,
 *		memory that it was reserving for a frame buffer.
 *		vm_page_create turns this memory into available pages.
 */

void vm_page_create(
	vm_offset_t	start,
	vm_offset_t	end)
{
	vm_offset_t paddr;
	vm_page_t m;

	for (paddr = round_page(start);
	     paddr < trunc_page(end);
	     paddr += PAGE_SIZE) {
		m = (vm_page_t) kmem_cache_alloc(&vm_page_cache);
		if (m == VM_PAGE_NULL)
			panic("vm_page_create");

		vm_page_init(m, paddr);
		vm_page_release(m, FALSE);
	}
}

/*
 *	vm_page_hash:
 *
 *	Distributes the object/offset key pair among hash buckets.
 *
 *	NOTE:	To get a good hash function, the bucket count should
 *		be a power of two.
 */
#define vm_page_hash(object, offset) \
	(((unsigned int)(vm_offset_t)object + (unsigned int)atop(offset)) \
		& vm_page_hash_mask)

/*
 *	vm_page_insert:		[ internal use only ]
 *
 *	Inserts the given mem entry into the object/object-page
 *	table and object list.
 *
 *	The object and page must be locked.
 */

void vm_page_insert(
	register vm_page_t	mem,
	register vm_object_t	object,
	register vm_offset_t	offset)
{
	register vm_page_bucket_t *bucket;

	VM_PAGE_CHECK(mem);

	if (mem->tabled)
		panic("vm_page_insert");

	/*
	 *	Record the object/offset pair in this page
	 */

	mem->object = object;
	mem->offset = offset;

	/*
	 *	Insert it into the object_object/offset hash table
	 */

	bucket = &vm_page_buckets[vm_page_hash(object, offset)];
	simple_lock(&bucket->lock);
	mem->next = bucket->pages;
	bucket->pages = mem;
	simple_unlock(&bucket->lock);

	/*
	 *	Now link into the object's list of backed pages.
	 */

	queue_enter(&object->memq, mem, vm_page_t, listq);
	mem->tabled = TRUE;

	/*
	 *	Show that the object has one more resident page.
	 */

	object->resident_page_count++;
	assert(object->resident_page_count >= 0);

	if (object->can_persist && (object->ref_count == 0))
		vm_object_cached_pages_update(1);

	/*
	 *	Detect sequential access and inactivate previous page.
	 *	We ignore busy pages.
	 */

	if (vm_page_deactivate_behind &&
	    (offset == object->last_alloc + PAGE_SIZE)) {
		vm_page_t	last_mem;

		last_mem = vm_page_lookup(object, object->last_alloc);
		if ((last_mem != VM_PAGE_NULL) && !last_mem->busy)
			vm_page_deactivate(last_mem);
	}
	object->last_alloc = offset;
}

/*
 *	vm_page_replace:
 *
 *	Exactly like vm_page_insert, except that we first
 *	remove any existing page at the given offset in object
 *	and we don't do deactivate-behind.
 *
 *	The object and page must be locked.
 */

void vm_page_replace(
	register vm_page_t	mem,
	register vm_object_t	object,
	register vm_offset_t	offset)
{
	register vm_page_bucket_t *bucket;

	VM_PAGE_CHECK(mem);

	if (mem->tabled)
		panic("vm_page_replace");

	/*
	 *	Record the object/offset pair in this page
	 */

	mem->object = object;
	mem->offset = offset;

	/*
	 *	Insert it into the object_object/offset hash table,
	 *	replacing any page that might have been there.
	 */

	bucket = &vm_page_buckets[vm_page_hash(object, offset)];
	simple_lock(&bucket->lock);
	if (bucket->pages) {
		vm_page_t *mp = &bucket->pages;
		register vm_page_t m = *mp;
		do {
			if (m->object == object && m->offset == offset) {
				/*
				 * Remove page from bucket and from object,
				 * and return it to the free list.
				 */
				*mp = m->next;
				queue_remove(&object->memq, m, vm_page_t,
					     listq);
				m->tabled = FALSE;
				object->resident_page_count--;

				if (object->can_persist
				    && (object->ref_count == 0))
					vm_object_cached_pages_update(-1);

				/*
				 * Return page to the free list.
				 * Note the page is not tabled now, so this
				 * won't self-deadlock on the bucket lock.
				 */

				vm_page_free(m);
				break;
			}
			mp = &m->next;
		} while ((m = *mp) != 0);
		mem->next = bucket->pages;
	} else {
		mem->next = VM_PAGE_NULL;
	}
	bucket->pages = mem;
	simple_unlock(&bucket->lock);

	/*
	 *	Now link into the object's list of backed pages.
	 */

	queue_enter(&object->memq, mem, vm_page_t, listq);
	mem->tabled = TRUE;

	/*
	 *	And show that the object has one more resident
	 *	page.
	 */

	object->resident_page_count++;
	assert(object->resident_page_count >= 0);

	if (object->can_persist && (object->ref_count == 0))
		vm_object_cached_pages_update(1);
}

/*
 *	vm_page_remove:		[ internal use only ]
 *
 *	Removes the given mem entry from the object/offset-page
 *	table and the object page list.
 *
 *	The object and page must be locked.
 */

void vm_page_remove(
	register vm_page_t	mem)
{
	register vm_page_bucket_t	*bucket;
	register vm_page_t	this;

	assert(mem->tabled);
	VM_PAGE_CHECK(mem);

	/*
	 *	Remove from the object_object/offset hash table
	 */

	bucket = &vm_page_buckets[vm_page_hash(mem->object, mem->offset)];
	simple_lock(&bucket->lock);
	if ((this = bucket->pages) == mem) {
		/* optimize for common case */

		bucket->pages = mem->next;
	} else {
		register vm_page_t	*prev;

		for (prev = &this->next;
		     (this = *prev) != mem;
		     prev = &this->next)
			continue;
		*prev = this->next;
	}
	simple_unlock(&bucket->lock);

	/*
	 *	Now remove from the object's list of backed pages.
	 */

	queue_remove(&mem->object->memq, mem, vm_page_t, listq);

	/*
	 *	And show that the object has one fewer resident
	 *	page.
	 */

	mem->object->resident_page_count--;

	mem->tabled = FALSE;

	if (mem->object->can_persist && (mem->object->ref_count == 0))
		vm_object_cached_pages_update(-1);
}

/*
 *	vm_page_lookup:
 *
 *	Returns the page associated with the object/offset
 *	pair specified; if none is found, VM_PAGE_NULL is returned.
 *
 *	The object must be locked.  No side effects.
 */

vm_page_t vm_page_lookup(
	register vm_object_t	object,
	register vm_offset_t	offset)
{
	register vm_page_t	mem;
	register vm_page_bucket_t *bucket;

	/*
	 *	Search the hash table for this object/offset pair
	 */

	bucket = &vm_page_buckets[vm_page_hash(object, offset)];

	simple_lock(&bucket->lock);
	for (mem = bucket->pages; mem != VM_PAGE_NULL; mem = mem->next) {
		VM_PAGE_CHECK(mem);
		if ((mem->object == object) && (mem->offset == offset))
			break;
	}
	simple_unlock(&bucket->lock);
	return mem;
}

/*
 *	vm_page_rename:
 *
 *	Move the given memory entry from its
 *	current object to the specified target object/offset.
 *
 *	The object must be locked.
 */
void vm_page_rename(
	register vm_page_t	mem,
	register vm_object_t	new_object,
	vm_offset_t		new_offset)
{
	/*
	 *	Changes to mem->object require the page lock because
	 *	the pageout daemon uses that lock to get the object.
	 */

	vm_page_lock_queues();
    	vm_page_remove(mem);
	vm_page_insert(mem, new_object, new_offset);
	vm_page_unlock_queues();
}

/*
 *	vm_page_init:
 *
 *	Initialize the fields in a new page.
 *	This takes a structure with random values and initializes it
 *	so that it can be given to vm_page_release or vm_page_insert.
 */
void vm_page_init(
	vm_page_t	mem,
	vm_offset_t	phys_addr)
{
	*mem = vm_page_template;
	mem->phys_addr = phys_addr;
}

/*
 *	vm_page_grab_fictitious:
 *
 *	Remove a fictitious page from the free list.
 *	Returns VM_PAGE_NULL if there are no free pages.
 */

vm_page_t vm_page_grab_fictitious(void)
{
	register vm_page_t m;

	simple_lock(&vm_page_queue_free_lock);
	m = vm_page_queue_fictitious;
	if (m != VM_PAGE_NULL) {
		vm_page_fictitious_count--;
		vm_page_queue_fictitious = (vm_page_t) m->pageq.next;
		m->free = FALSE;
	}
	simple_unlock(&vm_page_queue_free_lock);

	return m;
}

/*
 *	vm_page_release_fictitious:
 *
 *	Release a fictitious page to the free list.
 */

void vm_page_release_fictitious(
	register vm_page_t m)
{
	simple_lock(&vm_page_queue_free_lock);
	if (m->free)
		panic("vm_page_release_fictitious");
	m->free = TRUE;
	m->pageq.next = (queue_entry_t) vm_page_queue_fictitious;
	vm_page_queue_fictitious = m;
	vm_page_fictitious_count++;
	simple_unlock(&vm_page_queue_free_lock);
}

/*
 *	vm_page_more_fictitious:
 *
 *	Add more fictitious pages to the free list.
 *	Allowed to block.
 */

int vm_page_fictitious_quantum = 5;

void vm_page_more_fictitious(void)
{
	register vm_page_t m;
	int i;

	for (i = 0; i < vm_page_fictitious_quantum; i++) {
		m = (vm_page_t) kmem_cache_alloc(&vm_page_cache);
		if (m == VM_PAGE_NULL)
			panic("vm_page_more_fictitious");

		vm_page_init(m, vm_page_fictitious_addr);
		m->fictitious = TRUE;
		vm_page_release_fictitious(m);
	}
}

/*
 *	vm_page_convert:
 *
 *	Attempt to convert a fictitious page into a real page.
 */

boolean_t vm_page_convert(
	register vm_page_t m,
	boolean_t external)
{
	register vm_page_t real_m;

	real_m = vm_page_grab(external);
	if (real_m == VM_PAGE_NULL)
		return FALSE;

	m->phys_addr = real_m->phys_addr;
	m->fictitious = FALSE;

	real_m->phys_addr = vm_page_fictitious_addr;
	real_m->fictitious = TRUE;

	vm_page_release_fictitious(real_m);
	return TRUE;
}

/*
 *	vm_page_grab:
 *
 *	Remove a page from the free list.
 *	Returns VM_PAGE_NULL if the free list is too small.
 */

vm_page_t vm_page_grab(
	boolean_t external)
{
	register vm_page_t	mem;

	simple_lock(&vm_page_queue_free_lock);

	/*
	 *	Only let privileged threads (involved in pageout)
	 *	dip into the reserved pool or exceed the limit
	 *	for externally-managed pages.
	 */

	if (((vm_page_free_count < vm_page_free_reserved)
	     || (external
		 && (vm_page_external_count > vm_page_external_limit)))
	    && !current_thread()->vm_privilege) {
		simple_unlock(&vm_page_queue_free_lock);
		return VM_PAGE_NULL;
	}

	if (vm_page_queue_free == VM_PAGE_NULL)
		panic("vm_page_grab");

	if (--vm_page_free_count < vm_page_free_count_minimum)
		vm_page_free_count_minimum = vm_page_free_count;
	if (external)
		vm_page_external_count++;
	mem = vm_page_queue_free;
	vm_page_queue_free = (vm_page_t) mem->pageq.next;
	mem->free = FALSE;
	mem->extcounted = mem->external = external;
	simple_unlock(&vm_page_queue_free_lock);

	/*
	 *	Decide if we should poke the pageout daemon.
	 *	We do this if the free count is less than the low
	 *	water mark, or if the free count is less than the high
	 *	water mark (but above the low water mark) and the inactive
	 *	count is less than its target.
	 *
	 *	We don't have the counts locked ... if they change a little,
	 *	it doesn't really matter.
	 */

	if ((vm_page_free_count < vm_page_free_min) ||
	    ((vm_page_free_count < vm_page_free_target) &&
	     (vm_page_inactive_count < vm_page_inactive_target)))
		thread_wakeup((event_t) &vm_page_free_wanted);

	return mem;
}

vm_offset_t vm_page_grab_phys_addr()
{
	vm_page_t p = vm_page_grab(FALSE);
	if (p == VM_PAGE_NULL)
		return -1;
	else
		return p->phys_addr;
}

/*
 *	vm_page_grab_contiguous_pages:
 *
 *	Take N pages off the free list, the pages should
 *	cover a contiguous range of physical addresses.
 *	[Used by device drivers to cope with DMA limitations]
 *
 *	Returns the page descriptors in ascending order, or
 *	Returns KERN_RESOURCE_SHORTAGE if it could not.
 */

/* Biggest phys page number for the pages we handle in VM */

vm_size_t	vm_page_big_pagenum = 0;	/* Set this before call! */

kern_return_t
vm_page_grab_contiguous_pages(
	int		npages,
	vm_page_t	pages[],
	natural_t	*bits,
	boolean_t	external)
{
	register int	first_set;
	int		size, alloc_size;
	kern_return_t	ret;
	vm_page_t       mem, *prevmemp;

#ifndef	NBBY
#define	NBBY	8	/* size in bits of sizeof()`s unity */
#endif

#define	NBPEL	(sizeof(natural_t)*NBBY)

	size = (vm_page_big_pagenum + NBPEL - 1)
		& ~(NBPEL - 1);				/* in bits */

	size = size / NBBY;				/* in bytes */

	/*
	 * If we are called before the VM system is fully functional
	 * the invoker must provide us with the work space. [one bit
	 * per page starting at phys 0 and up to vm_page_big_pagenum]
	 */
	if (bits == 0) {
		alloc_size = round_page(size);
		if (kmem_alloc_wired(kernel_map,
				     (vm_offset_t *)&bits,
				     alloc_size)
			!= KERN_SUCCESS)
		    return KERN_RESOURCE_SHORTAGE;
	} else
		alloc_size = 0;

	memset(bits, 0, size);

	/*
	 * A very large granularity call, its rare so that is ok
	 */
	simple_lock(&vm_page_queue_free_lock);

	/*
	 *	Do not dip into the reserved pool.
	 */

	if ((vm_page_free_count < vm_page_free_reserved)
	    || (vm_page_external_count >= vm_page_external_limit)) {
		printf_once("no more room for vm_page_grab_contiguous_pages");
		simple_unlock(&vm_page_queue_free_lock);
		return KERN_RESOURCE_SHORTAGE;
	}

	/*
	 *	First pass through, build a big bit-array of
	 *	the pages that are free.  It is not going to
	 *	be too large anyways, in 4k we can fit info
	 *	for 32k pages.
	 */
	mem = vm_page_queue_free;
	while (mem) {
		register int word_index, bit_index;

		bit_index = (mem->phys_addr >> PAGE_SHIFT);
		word_index = bit_index / NBPEL;
		bit_index = bit_index - (word_index * NBPEL);
		bits[word_index] |= 1 << bit_index;

		mem = (vm_page_t) mem->pageq.next;
	}

	/*
	 *	Second loop. Scan the bit array for NPAGES
	 *	contiguous bits.  That gives us, if any,
	 *	the range of pages we will be grabbing off
	 *	the free list.
	 */
	{
	    register int	bits_so_far = 0, i;

		first_set = 0;

		for (i = 0; i < size; i += sizeof(natural_t)) {

		    register natural_t	v = bits[i / sizeof(natural_t)];
		    register int	bitpos;

		    /*
		     * Bitscan this one word
		     */
		    if (v) {
			/*
			 * keep counting them beans ?
			 */
			bitpos = 0;

			if (bits_so_far) {
count_ones:
			    while (v & 1) {
				bitpos++;
				/*
				 * got enough beans ?
				 */
				if (++bits_so_far == npages)
				    goto found_em;
				v >>= 1;
			    }
			    /* if we are being lucky, roll again */
			    if (bitpos == NBPEL)
			    	continue;
			}

			/*
			 * search for beans here
			 */
			bits_so_far = 0;
			while ((bitpos < NBPEL) && ((v & 1) == 0)) {
			    bitpos++;
			    v >>= 1;
			}
			if (v & 1) {
			    first_set = (i * NBBY) + bitpos;
			    goto count_ones;
			}
		    }
		    /*
		     * No luck
		     */
		    bits_so_far = 0;
		}
	}

	/*
	 *	We could not find enough contiguous pages.
	 */
	simple_unlock(&vm_page_queue_free_lock);

	printf_once("no contiguous room for vm_page_grab_contiguous_pages");
	ret = KERN_RESOURCE_SHORTAGE;
	goto out;

	/*
	 *	Final pass. Now we know which pages we want.
	 *	Scan the list until we find them all, grab
	 *	pages as we go.  FIRST_SET tells us where
	 *	in the bit-array our pages start.
	 */
found_em:
	vm_page_free_count -= npages;
	if (vm_page_free_count < vm_page_free_count_minimum)
		vm_page_free_count_minimum = vm_page_free_count;
	if (external)
		vm_page_external_count += npages;
	{
	    register vm_offset_t	first_phys, last_phys;

	    /* cache values for compare */
	    first_phys = first_set << PAGE_SHIFT;
	    last_phys = first_phys + (npages << PAGE_SHIFT);/* not included */

	    /* running pointers */
	    mem = vm_page_queue_free;
	    prevmemp = &vm_page_queue_free;

	    while (mem) {

		register vm_offset_t	addr;

		addr = mem->phys_addr;

		if ((addr >= first_phys) &&
		    (addr <  last_phys)) {
		    *prevmemp = (vm_page_t) mem->pageq.next;
		    pages[(addr - first_phys) >> PAGE_SHIFT] = mem;
		    mem->free = FALSE;
		    mem->extcounted = mem->external = external;
		    /*
		     * Got them all ?
		     */
		    if (--npages == 0) break;
		} else
		    prevmemp = (vm_page_t *) &mem->pageq.next;

		mem = (vm_page_t) mem->pageq.next;
	    }
	}

	simple_unlock(&vm_page_queue_free_lock);

	/*
	 *	Decide if we should poke the pageout daemon.
	 *	We do this if the free count is less than the low
	 *	water mark, or if the free count is less than the high
	 *	water mark (but above the low water mark) and the inactive
	 *	count is less than its target.
	 *
	 *	We don't have the counts locked ... if they change a little,
	 *	it doesn't really matter.
	 */

	if ((vm_page_free_count < vm_page_free_min) ||
	    ((vm_page_free_count < vm_page_free_target) &&
	     (vm_page_inactive_count < vm_page_inactive_target)))
		thread_wakeup(&vm_page_free_wanted);

	ret = KERN_SUCCESS;
out:
	if (alloc_size)
		kmem_free(kernel_map, (vm_offset_t) bits, alloc_size);

	return ret;
}

/*
 *	vm_page_release:
 *
 *	Return a page to the free list.
 */

void vm_page_release(
	register vm_page_t	mem,
	boolean_t external)
{
	simple_lock(&vm_page_queue_free_lock);
	if (mem->free)
		panic("vm_page_release");
	mem->free = TRUE;
	mem->pageq.next = (queue_entry_t) vm_page_queue_free;
	vm_page_queue_free = mem;
	vm_page_free_count++;
	if (external)
		vm_page_external_count--;

	/*
	 *	Check if we should wake up someone waiting for page.
	 *	But don't bother waking them unless they can allocate.
	 *
	 *	We wakeup only one thread, to prevent starvation.
	 *	Because the scheduling system handles wait queues FIFO,
	 *	if we wakeup all waiting threads, one greedy thread
	 *	can starve multiple niceguy threads.  When the threads
	 *	all wakeup, the greedy threads runs first, grabs the page,
	 *	and waits for another page.  It will be the first to run
	 *	when the next page is freed.
	 *
	 *	However, there is a slight danger here.
	 *	The thread we wake might not use the free page.
	 *	Then the other threads could wait indefinitely
	 *	while the page goes unused.  To forestall this,
	 *	the pageout daemon will keep making free pages
	 *	as long as vm_page_free_wanted is non-zero.
	 */

	if ((vm_page_free_wanted > 0) &&
	    (vm_page_free_count >= vm_page_free_reserved)) {
		vm_page_free_wanted--;
		thread_wakeup_one((event_t) &vm_page_free_count);
	}

	simple_unlock(&vm_page_queue_free_lock);
}

/*
 *	vm_page_wait:
 *
 *	Wait for a page to become available.
 *	If there are plenty of free pages, then we don't sleep.
 */

void vm_page_wait(
	void (*continuation)(void))
{

	/*
	 *	We can't use vm_page_free_reserved to make this
	 *	determination.  Consider: some thread might
	 *	need to allocate two pages.  The first allocation
	 *	succeeds, the second fails.  After the first page is freed,
	 *	a call to vm_page_wait must really block.
	 */

	simple_lock(&vm_page_queue_free_lock);
	if ((vm_page_free_count < vm_page_free_target)
	    || (vm_page_external_count > vm_page_external_limit)) {
		if (vm_page_free_wanted++ == 0)
			thread_wakeup((event_t)&vm_page_free_wanted);
		assert_wait((event_t)&vm_page_free_count, FALSE);
		simple_unlock(&vm_page_queue_free_lock);
		if (continuation != 0) {
			counter(c_vm_page_wait_block_user++);
			thread_block(continuation);
		} else {
			counter(c_vm_page_wait_block_kernel++);
			thread_block((void (*)(void)) 0);
		}
	} else
		simple_unlock(&vm_page_queue_free_lock);
}

/*
 *	vm_page_alloc:
 *
 *	Allocate and return a memory cell associated
 *	with this VM object/offset pair.
 *
 *	Object must be locked.
 */

vm_page_t vm_page_alloc(
	vm_object_t	object,
	vm_offset_t	offset)
{
	register vm_page_t	mem;

	mem = vm_page_grab(!object->internal);
	if (mem == VM_PAGE_NULL)
		return VM_PAGE_NULL;

	vm_page_lock_queues();
	vm_page_insert(mem, object, offset);
	vm_page_unlock_queues();

	return mem;
}

/*
 *	vm_page_free:
 *
 *	Returns the given page to the free list,
 *	disassociating it with any VM object.
 *
 *	Object and page queues must be locked prior to entry.
 */
void vm_page_free(
	register vm_page_t	mem)
{
	if (mem->free)
		panic("vm_page_free");

	if (mem->tabled)
		vm_page_remove(mem);
	VM_PAGE_QUEUES_REMOVE(mem);

	if (mem->wire_count != 0) {
		if (!mem->private && !mem->fictitious)
			vm_page_wire_count--;
		mem->wire_count = 0;
	}

	if (mem->laundry) {
		vm_page_laundry_count--;
		mem->laundry = FALSE;
	}

	PAGE_WAKEUP_DONE(mem);

	if (mem->absent)
		vm_object_absent_release(mem->object);

	/*
	 *	XXX The calls to vm_page_init here are
	 *	really overkill.
	 */

	if (mem->private || mem->fictitious) {
		vm_page_init(mem, vm_page_fictitious_addr);
		mem->fictitious = TRUE;
		vm_page_release_fictitious(mem);
	} else {
		int external = mem->external && mem->extcounted;
		vm_page_init(mem, mem->phys_addr);
		vm_page_release(mem, external);
	}
}

/*
 *	vm_page_wire:
 *
 *	Mark this page as wired down by yet
 *	another map, removing it from paging queues
 *	as necessary.
 *
 *	The page's object and the page queues must be locked.
 */
void vm_page_wire(
	register vm_page_t	mem)
{
	VM_PAGE_CHECK(mem);

	if (mem->wire_count == 0) {
		VM_PAGE_QUEUES_REMOVE(mem);
		if (!mem->private && !mem->fictitious)
			vm_page_wire_count++;
	}
	mem->wire_count++;
}

/*
 *	vm_page_unwire:
 *
 *	Release one wiring of this page, potentially
 *	enabling it to be paged again.
 *
 *	The page's object and the page queues must be locked.
 */
void vm_page_unwire(
	register vm_page_t	mem)
{
	VM_PAGE_CHECK(mem);

	if (--mem->wire_count == 0) {
		queue_enter(&vm_page_queue_active, mem, vm_page_t, pageq);
		vm_page_active_count++;
		mem->active = TRUE;
		if (!mem->private && !mem->fictitious)
			vm_page_wire_count--;
	}
}

/*
 *	vm_page_deactivate:
 *
 *	Returns the given page to the inactive list,
 *	indicating that no physical maps have access
 *	to this page.  [Used by the physical mapping system.]
 *
 *	The page queues must be locked.
 */
void vm_page_deactivate(
	register vm_page_t	m)
{
	VM_PAGE_CHECK(m);

	/*
	 *	This page is no longer very interesting.  If it was
	 *	interesting (active or inactive/referenced), then we
	 *	clear the reference bit and (re)enter it in the
	 *	inactive queue.  Note wired pages should not have
	 *	their reference bit cleared.
	 */

	if (m->active || (m->inactive && m->reference)) {
		if (!m->fictitious && !m->absent)
			pmap_clear_reference(m->phys_addr);
		m->reference = FALSE;
		VM_PAGE_QUEUES_REMOVE(m);
	}
	if (m->wire_count == 0 && !m->inactive) {
		queue_enter(&vm_page_queue_inactive, m, vm_page_t, pageq);
		m->inactive = TRUE;
		vm_page_inactive_count++;
	}
}

/*
 *	vm_page_activate:
 *
 *	Put the specified page on the active list (if appropriate).
 *
 *	The page queues must be locked.
 */

void vm_page_activate(
	register vm_page_t	m)
{
	VM_PAGE_CHECK(m);

	if (m->inactive) {
		queue_remove(&vm_page_queue_inactive, m, vm_page_t,
						pageq);
		vm_page_inactive_count--;
		m->inactive = FALSE;
	}
	if (m->wire_count == 0) {
		if (m->active)
			panic("vm_page_activate: already active");

		queue_enter(&vm_page_queue_active, m, vm_page_t, pageq);
		m->active = TRUE;
		vm_page_active_count++;
	}
}

/*
 *	vm_page_zero_fill:
 *
 *	Zero-fill the specified page.
 */
void vm_page_zero_fill(
	vm_page_t	m)
{
	VM_PAGE_CHECK(m);

	pmap_zero_page(m->phys_addr);
}

/*
 *	vm_page_copy:
 *
 *	Copy one page to another
 */

void vm_page_copy(
	vm_page_t	src_m,
	vm_page_t	dest_m)
{
	VM_PAGE_CHECK(src_m);
	VM_PAGE_CHECK(dest_m);

	pmap_copy_page(src_m->phys_addr, dest_m->phys_addr);
}

#if	MACH_VM_DEBUG
/*
 *	Routine:	vm_page_info
 *	Purpose:
 *		Return information about the global VP table.
 *		Fills the buffer with as much information as possible
 *		and returns the desired size of the buffer.
 *	Conditions:
 *		Nothing locked.  The caller should provide
 *		possibly-pageable memory.
 */

unsigned int
vm_page_info(
	hash_info_bucket_t *info,
	unsigned int	count)
{
	int i;

	if (vm_page_bucket_count < count)
		count = vm_page_bucket_count;

	for (i = 0; i < count; i++) {
		vm_page_bucket_t *bucket = &vm_page_buckets[i];
		unsigned int bucket_count = 0;
		vm_page_t m;

		simple_lock(&bucket->lock);
		for (m = bucket->pages; m != VM_PAGE_NULL; m = m->next)
			bucket_count++;
		simple_unlock(&bucket->lock);

		/* don't touch pageable memory while holding locks */
		info[i].hib_count = bucket_count;
	}

	return vm_page_bucket_count;
}
#endif	/* MACH_VM_DEBUG */


#if	MACH_KDB
#define	printf	kdbprintf

/*
 *	Routine:	vm_page_print [exported]
 */
void		vm_page_print(p)
	vm_page_t	p;
{
	iprintf("Page 0x%X: object 0x%X,", (vm_offset_t) p, (vm_offset_t) p->object);
	 printf(" offset 0x%X", (vm_offset_t) p->offset);
	 printf("wire_count %d,", p->wire_count);
	 printf(" %s",
		(p->active ? "active" : (p->inactive ? "inactive" : "loose")));
	 printf("%s",
		(p->free ? " free" : ""));
	 printf("%s ",
		(p->laundry ? " laundry" : ""));
	 printf("%s",
		(p->dirty ? "dirty" : "clean"));
	 printf("%s",
	 	(p->busy ? " busy" : ""));
	 printf("%s",
	 	(p->absent ? " absent" : ""));
	 printf("%s",
	 	(p->error ? " error" : ""));
	 printf("%s",
		(p->fictitious ? " fictitious" : ""));
	 printf("%s",
		(p->private ? " private" : ""));
	 printf("%s",
		(p->wanted ? " wanted" : ""));
	 printf("%s,",
		(p->tabled ? "" : "not_tabled"));
	 printf("phys_addr = 0x%X, lock = 0x%X, unlock_request = 0x%X\n",
	 	(vm_offset_t) p->phys_addr,
		(vm_offset_t) p->page_lock,
		(vm_offset_t) p->unlock_request);
}
#endif	/* MACH_KDB */