freebsd-nq/sys/vm/swap_pager.c

/*
 * Copyright (c) 1994 John S. Dyson
 * Copyright (c) 1990 University of Utah.
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * the Systems Programming Group of the University of Utah Computer
 * Science Department.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
 *
 *	@(#)swap_pager.c	8.9 (Berkeley) 3/21/94
 * $Id: swap_pager.c,v 1.93 1998/04/15 17:47:35 bde Exp $
 */

/*
 * Quick hack to page to dedicated partition(s).
 * TODO:
 *	Add multiprocessor locks
 *	Deal with async writes in a better fashion
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/malloc.h>
#include <sys/vmmeter.h>
#include <sys/rlist.h>

#ifndef MAX_PAGEOUT_CLUSTER
#define MAX_PAGEOUT_CLUSTER 16
#endif

#ifndef NPENDINGIO
#define NPENDINGIO	16
#endif

#define SWB_NPAGES MAX_PAGEOUT_CLUSTER

#include <vm/vm.h>
#include <vm/vm_prot.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>
#include <vm/vm_pageout.h>
#include <vm/swap_pager.h>
#include <vm/vm_extern.h>

static int nswiodone;
int swap_pager_full;
extern int vm_swap_size;
static int suggest_more_swap = 0;
static int no_swap_space = 1;
static int max_pageout_cluster;
struct rlisthdr swaplist;

TAILQ_HEAD(swpclean, swpagerclean);

typedef struct swpagerclean *swp_clean_t;

static struct swpagerclean {
	TAILQ_ENTRY(swpagerclean) spc_list;
	int spc_flags;
	struct buf *spc_bp;
	vm_object_t spc_object;
	vm_offset_t spc_kva;
	int spc_first;
	int spc_count;
	vm_page_t spc_m[MAX_PAGEOUT_CLUSTER];
} swcleanlist[NPENDINGIO];


/* spc_flags values */
#define SPC_ERROR	0x01

#define SWB_EMPTY (-1)

/* list of completed page cleans */
static struct swpclean swap_pager_done;

/* list of pending page cleans */
static struct swpclean swap_pager_inuse;

/* list of free pager clean structs */
static struct swpclean swap_pager_free;
static int swap_pager_free_count;
static int swap_pager_free_pending;

/* list of "named" anon region objects */
static struct pagerlst swap_pager_object_list;

/* list of "unnamed" anon region objects */
struct pagerlst swap_pager_un_object_list;

#define	SWAP_FREE_NEEDED	0x1	/* need a swap block */
#define SWAP_FREE_NEEDED_BY_PAGEOUT 0x2
static int swap_pager_needflags;

static struct pagerlst *swp_qs[] = {
	&swap_pager_object_list, &swap_pager_un_object_list, (struct pagerlst *) 0
};

/*
 * pagerops for OBJT_SWAP - "swap pager".
 */
static vm_object_t
		swap_pager_alloc __P((void *handle, vm_size_t size,
				      vm_prot_t prot, vm_ooffset_t offset));
static void	swap_pager_dealloc __P((vm_object_t object));
static boolean_t
		swap_pager_haspage __P((vm_object_t object, vm_pindex_t pindex,
					int *before, int *after));
static int	swap_pager_getpages __P((vm_object_t, vm_page_t *, int, int));
static void	swap_pager_init __P((void));
static void spc_free __P((swp_clean_t));

struct pagerops swappagerops = {
	swap_pager_init,
	swap_pager_alloc,
	swap_pager_dealloc,
	swap_pager_getpages,
	swap_pager_putpages,
	swap_pager_haspage,
	swap_pager_sync
};

static int npendingio;
static int dmmin;
int dmmax;

static int	swap_pager_block_index __P((vm_pindex_t pindex));
static int	swap_pager_block_offset __P((vm_pindex_t pindex));
static daddr_t *swap_pager_diskaddr __P((vm_object_t object,
					  vm_pindex_t pindex, int *valid));
static void	swap_pager_finish __P((swp_clean_t spc));
static void	swap_pager_free_swap __P((vm_object_t object));
static void	swap_pager_freeswapspace __P((vm_object_t object,
					      unsigned int from,
					      unsigned int to));
static int	swap_pager_getswapspace __P((vm_object_t object,
					     unsigned int amount,
					     daddr_t *rtval));
static void	swap_pager_iodone __P((struct buf *));
static void	swap_pager_iodone1 __P((struct buf *bp));
static void	swap_pager_reclaim __P((void));
static void	swap_pager_ridpages __P((vm_page_t *m, int count,
					 int reqpage));
static void	swap_pager_setvalid __P((vm_object_t object,
					 vm_offset_t offset, int valid));
static __inline void	swapsizecheck __P((void));

#define SWAPLOW (vm_swap_size < (512 * btodb(PAGE_SIZE)))

static __inline void
swapsizecheck()
{
	if (vm_swap_size < 128 * btodb(PAGE_SIZE)) {
		if (swap_pager_full == 0)
			printf("swap_pager: out of swap space\n");
		swap_pager_full = 1;
	} else if (vm_swap_size > 192 * btodb(PAGE_SIZE))
		swap_pager_full = 0;
}

static void
swap_pager_init()
{
	int maxsafepending;
	TAILQ_INIT(&swap_pager_object_list);
	TAILQ_INIT(&swap_pager_un_object_list);

	/*
	 * Initialize clean lists
	 */
	TAILQ_INIT(&swap_pager_inuse);
	TAILQ_INIT(&swap_pager_done);
	TAILQ_INIT(&swap_pager_free);
	swap_pager_free_count = 0;

	/*
	 * Calculate the swap allocation constants.
	 */
	dmmin = PAGE_SIZE / DEV_BSIZE;
	dmmax = btodb(SWB_NPAGES * PAGE_SIZE) * 2;

	maxsafepending = cnt.v_free_min - cnt.v_free_reserved;
	npendingio = NPENDINGIO;
	max_pageout_cluster = MAX_PAGEOUT_CLUSTER;

	if ((2 * NPENDINGIO * MAX_PAGEOUT_CLUSTER) > maxsafepending) {
		max_pageout_cluster = MAX_PAGEOUT_CLUSTER / 2;
		npendingio = maxsafepending / (2 * max_pageout_cluster);
		if (npendingio < 2)
			npendingio = 2;
	}
}

void
swap_pager_swap_init()
{
	swp_clean_t spc;
	struct buf *bp;
	int i;

	/*
	 * kva's are allocated here so that we dont need to keep doing
	 * kmem_alloc pageables at runtime
	 */
	for (i = 0, spc = swcleanlist; i < npendingio; i++, spc++) {
		spc->spc_kva = kmem_alloc_pageable(pager_map, PAGE_SIZE * max_pageout_cluster);
		if (!spc->spc_kva) {
			break;
		}
		spc->spc_bp = malloc(sizeof(*bp), M_TEMP, M_KERNEL);
		if (!spc->spc_bp) {
			kmem_free_wakeup(pager_map, spc->spc_kva, PAGE_SIZE);
			break;
		}
		spc->spc_flags = 0;
		TAILQ_INSERT_TAIL(&swap_pager_free, spc, spc_list);
		swap_pager_free_count++;
	}
}

int
swap_pager_swp_alloc(object, wait)
	vm_object_t object;
	int wait;
{
	sw_blk_t swb;
	int nblocks;
	int i, j;

	nblocks = (object->size + SWB_NPAGES - 1) / SWB_NPAGES;
	swb = malloc(nblocks * sizeof(*swb), M_VMPGDATA, wait);
	if (swb == NULL)
		return 1;

	for (i = 0; i < nblocks; i++) {
		swb[i].swb_valid = 0;
		swb[i].swb_locked = 0;
		for (j = 0; j < SWB_NPAGES; j++)
			swb[i].swb_block[j] = SWB_EMPTY;
	}

	object->un_pager.swp.swp_nblocks = nblocks;
	object->un_pager.swp.swp_allocsize = 0;
	object->un_pager.swp.swp_blocks = swb;
	object->un_pager.swp.swp_poip = 0;

	if (object->handle != NULL) {
		TAILQ_INSERT_TAIL(&swap_pager_object_list, object, pager_object_list);
	} else {
		TAILQ_INSERT_TAIL(&swap_pager_un_object_list, object, pager_object_list);
	}

	return 0;
}

/*
 * Allocate an object and associated resources.
 * Note that if we are called from the pageout daemon (handle == NULL)
 * we should not wait for memory as it could resulting in deadlock.
 */
static vm_object_t
swap_pager_alloc(void *handle, vm_size_t size, vm_prot_t prot,
		 vm_ooffset_t offset)
{
	vm_object_t object;

	/*
	 * If this is a "named" anonymous region, look it up and use the
	 * object if it exists, otherwise allocate a new one.
	 */
	if (handle) {
		object = vm_pager_object_lookup(&swap_pager_object_list, handle);
		if (object != NULL) {
			vm_object_reference(object);
		} else {
			/*
			 * XXX - there is a race condition here. Two processes
			 * can request the same named object simultaneuously,
			 * and if one blocks for memory, the result is a disaster.
			 * Probably quite rare, but is yet another reason to just
			 * rip support of "named anonymous regions" out altogether.
			 */
			object = vm_object_allocate(OBJT_SWAP,
				OFF_TO_IDX(offset + PAGE_MASK) + size);
			object->handle = handle;
			(void) swap_pager_swp_alloc(object, M_WAITOK);
		}
	} else {
		object = vm_object_allocate(OBJT_SWAP,
			OFF_TO_IDX(offset + PAGE_MASK) + size);
		(void) swap_pager_swp_alloc(object, M_WAITOK);
	}

	return (object);
}

/*
 * returns disk block associated with pager and offset
 * additionally, as a side effect returns a flag indicating
 * if the block has been written
 */

static __inline daddr_t *
swap_pager_diskaddr(object, pindex, valid)
	vm_object_t object;
	vm_pindex_t pindex;
	int *valid;
{
	register sw_blk_t swb;
	int ix;

	if (valid)
		*valid = 0;
	ix = pindex / SWB_NPAGES;
	if ((ix >= object->un_pager.swp.swp_nblocks) ||
	    (pindex >= object->size)) {
		return (FALSE);
	}
	swb = &object->un_pager.swp.swp_blocks[ix];
	ix = pindex % SWB_NPAGES;
	if (valid)
		*valid = swb->swb_valid & (1 << ix);
	return &swb->swb_block[ix];
}

/*
 * Utility routine to set the valid (written) bit for
 * a block associated with a pager and offset
 */
static void
swap_pager_setvalid(object, offset, valid)
	vm_object_t object;
	vm_offset_t offset;
	int valid;
{
	register sw_blk_t swb;
	int ix;

	ix = offset / SWB_NPAGES;
	if (ix >= object->un_pager.swp.swp_nblocks)
		return;

	swb = &object->un_pager.swp.swp_blocks[ix];
	ix = offset % SWB_NPAGES;
	if (valid)
		swb->swb_valid |= (1 << ix);
	else
		swb->swb_valid &= ~(1 << ix);
	return;
}

/*
 * this routine allocates swap space with a fragmentation
 * minimization policy.
 */
static int
swap_pager_getswapspace(object, amount, rtval)
	vm_object_t object;
	unsigned int amount;
	daddr_t *rtval;
{
	unsigned location;

	vm_swap_size -= amount;
	if (!suggest_more_swap && (vm_swap_size < btodb(cnt.v_page_count * PAGE_SIZE))) {
		printf("swap_pager: suggest more swap space: %d MB\n",
			(2 * cnt.v_page_count * (PAGE_SIZE / 1024)) / 1000);
		suggest_more_swap = 1;
	}
		
	if (!rlist_alloc(&swaplist, amount, &location)) {
		vm_swap_size += amount;
		return 0;
	} else {
		swapsizecheck();
		object->un_pager.swp.swp_allocsize += amount;
		*rtval = location;
		return 1;
	}
}

/*
 * this routine frees swap space with a fragmentation
 * minimization policy.
 */
static void
swap_pager_freeswapspace(object, from, to)
	vm_object_t object;
	unsigned int from;
	unsigned int to;
{
	rlist_free(&swaplist, from, to);
	vm_swap_size += (to - from) + 1;
	object->un_pager.swp.swp_allocsize -= (to - from) + 1;
	swapsizecheck();
}
/*
 * this routine frees swap blocks from a specified pager
 */
void
swap_pager_freespace(object, start, size)
	vm_object_t object;
	vm_pindex_t start;
	vm_size_t size;
{
	vm_pindex_t i;
	int s;

	s = splvm();
	for (i = start; i < start + size; i += 1) {
		int valid;
		daddr_t *addr = swap_pager_diskaddr(object, i, &valid);

		if (addr && *addr != SWB_EMPTY) {
			swap_pager_freeswapspace(object, *addr, *addr + btodb(PAGE_SIZE) - 1);
			if (valid) {
				swap_pager_setvalid(object, i, 0);
			}
			*addr = SWB_EMPTY;
		}
	}
	splx(s);
}

/*
 * same as freespace, but don't free, just force a DMZ next time
 */
void
swap_pager_dmzspace(object, start, size)
	vm_object_t object;
	vm_pindex_t start;
	vm_size_t size;
{
	vm_pindex_t i;
	int s;

	s = splvm();
	for (i = start; i < start + size; i += 1) {
		int valid;
		daddr_t *addr = swap_pager_diskaddr(object, i, &valid);

		if (addr && *addr != SWB_EMPTY) {
			if (valid) {
				swap_pager_setvalid(object, i, 0);
			}
		}
	}
	splx(s);
}

static void
swap_pager_free_swap(object)
	vm_object_t object;
{
	register int i, j;
	register sw_blk_t swb;
	int first_block=0, block_count=0;
	int s;
	/*
	 * Free left over swap blocks
	 */
	swb = object->un_pager.swp.swp_blocks;
	if (swb == NULL) {
		return;
	}

	s = splvm();
	for (i = 0; i < object->un_pager.swp.swp_nblocks; i++, swb++) {
		for (j = 0; j < SWB_NPAGES; j++) {
			if (swb->swb_block[j] != SWB_EMPTY) {
				/*
   				 * initially the length of the run is zero
   				 */
				if (block_count == 0) {
					first_block = swb->swb_block[j];
					block_count = btodb(PAGE_SIZE);
					swb->swb_block[j] = SWB_EMPTY;
				/*
   				 * if the new block can be included into the current run
   				 */
				} else if (swb->swb_block[j] == first_block + block_count) {
					block_count += btodb(PAGE_SIZE);
					swb->swb_block[j] = SWB_EMPTY;
				/*
   				 * terminate the previous run, and start a new one
   				 */
				} else {
					swap_pager_freeswapspace(object, first_block,
   					(unsigned) first_block + block_count - 1);
					first_block = swb->swb_block[j];
					block_count = btodb(PAGE_SIZE);
					swb->swb_block[j] = SWB_EMPTY;
				}
			}
		}
	}

	if (block_count) {
		swap_pager_freeswapspace(object, first_block,
		   	 (unsigned) first_block + block_count - 1);
	}
	splx(s);
}


/*
 * swap_pager_reclaim frees up over-allocated space from all pagers
 * this eliminates internal fragmentation due to allocation of space
 * for segments that are never swapped to. It has been written so that
 * it does not block until the rlist_free operation occurs; it keeps
 * the queues consistant.
 */

/*
 * Maximum number of blocks (pages) to reclaim per pass
 */
#define MAXRECLAIM 128

static void
swap_pager_reclaim()
{
	vm_object_t object;
	int i, j, k;
	int s;
	int reclaimcount;
	static struct {
		int address;
		vm_object_t object;
	} reclaims[MAXRECLAIM];
	static int in_reclaim;

	/*
	 * allow only one process to be in the swap_pager_reclaim subroutine
	 */
	s = splvm();
	if (in_reclaim) {
		tsleep(&in_reclaim, PSWP, "swrclm", 0);
		splx(s);
		return;
	}
	in_reclaim = 1;
	reclaimcount = 0;

	/* for each pager queue */
	for (k = 0; swp_qs[k]; k++) {

		object = TAILQ_FIRST(swp_qs[k]);
		while (object && (reclaimcount < MAXRECLAIM)) {

			/*
			 * see if any blocks associated with a pager has been
			 * allocated but not used (written)
			 */
			if ((object->flags & OBJ_DEAD) == 0 &&
				(object->paging_in_progress == 0)) {
				for (i = 0; i < object->un_pager.swp.swp_nblocks; i++) {
					sw_blk_t swb = &object->un_pager.swp.swp_blocks[i];

					if (swb->swb_locked)
						continue;
					for (j = 0; j < SWB_NPAGES; j++) {
						if (swb->swb_block[j] != SWB_EMPTY &&
						    (swb->swb_valid & (1 << j)) == 0) {
							reclaims[reclaimcount].address = swb->swb_block[j];
							reclaims[reclaimcount++].object = object;
							swb->swb_block[j] = SWB_EMPTY;
							if (reclaimcount >= MAXRECLAIM)
								goto rfinished;
						}
					}
				}
			}
			object = TAILQ_NEXT(object, pager_object_list);
		}
	}

rfinished:

	/*
	 * free the blocks that have been added to the reclaim list
	 */
	for (i = 0; i < reclaimcount; i++) {
		swap_pager_freeswapspace(reclaims[i].object,
		    reclaims[i].address, reclaims[i].address + btodb(PAGE_SIZE) - 1);
	}
	splx(s);
	in_reclaim = 0;
	wakeup(&in_reclaim);
}


/*
 * swap_pager_copy copies blocks from one pager to another and
 * destroys the source pager
 */

void
swap_pager_copy(srcobject, srcoffset, dstobject, dstoffset, offset, destroysource)
	vm_object_t srcobject;
	vm_pindex_t srcoffset;
	vm_object_t dstobject;
	vm_pindex_t dstoffset;
	vm_pindex_t offset;
	int destroysource;
{
	vm_pindex_t i;
	int origsize;
	int s;

	if (vm_swap_size)
		no_swap_space = 0;

	origsize = srcobject->un_pager.swp.swp_allocsize;

	/*
	 * remove the source object from the swap_pager internal queue
	 */
	if (srcobject->handle == NULL) {
		TAILQ_REMOVE(&swap_pager_un_object_list, srcobject, pager_object_list);
	} else {
		TAILQ_REMOVE(&swap_pager_object_list, srcobject, pager_object_list);
	}

	s = splvm();
	while (srcobject->un_pager.swp.swp_poip) {
		tsleep(srcobject, PVM, "spgout", 0);
	}

	/*
	 * clean all of the pages that are currently active and finished
	 */
	if (swap_pager_free_pending)
		swap_pager_sync();

	/*
	 * transfer source to destination
	 */
	for (i = 0; i < dstobject->size; i += 1) {
		int srcvalid, dstvalid;
		daddr_t *srcaddrp = swap_pager_diskaddr(srcobject, i + offset + srcoffset,
						    &srcvalid);
		daddr_t *dstaddrp;

		/*
		 * see if the source has space allocated
		 */
		if (srcaddrp && *srcaddrp != SWB_EMPTY) {
			/*
			 * if the source is valid and the dest has no space,
			 * then copy the allocation from the srouce to the
			 * dest.
			 */
			if (srcvalid) {
				dstaddrp = swap_pager_diskaddr(dstobject, i + dstoffset,
							&dstvalid);
				/*
				 * if the dest already has a valid block,
				 * deallocate the source block without
				 * copying.
				 */
				if (!dstvalid && dstaddrp && *dstaddrp != SWB_EMPTY) {
					swap_pager_freeswapspace(dstobject, *dstaddrp,
						*dstaddrp + btodb(PAGE_SIZE) - 1);
					*dstaddrp = SWB_EMPTY;
				}
				if (dstaddrp && *dstaddrp == SWB_EMPTY) {
					*dstaddrp = *srcaddrp;
					*srcaddrp = SWB_EMPTY;
					dstobject->un_pager.swp.swp_allocsize += btodb(PAGE_SIZE);
					srcobject->un_pager.swp.swp_allocsize -= btodb(PAGE_SIZE);
					swap_pager_setvalid(dstobject, i + dstoffset, 1);
				}
			}
			/*
			 * if the source is not empty at this point, then
			 * deallocate the space.
			 */
			if (*srcaddrp != SWB_EMPTY) {
				swap_pager_freeswapspace(srcobject, *srcaddrp,
					*srcaddrp + btodb(PAGE_SIZE) - 1);
				*srcaddrp = SWB_EMPTY;
			}
		}
	}
	splx(s);

	/*
	 * Free left over swap blocks
	 */
	if (destroysource) {
		swap_pager_free_swap(srcobject);

		if (srcobject->un_pager.swp.swp_allocsize) {
			printf("swap_pager_copy: *warning* pager with %d blocks (orig: %d)\n",
			    srcobject->un_pager.swp.swp_allocsize, origsize);
		}

		free(srcobject->un_pager.swp.swp_blocks, M_VMPGDATA);
		srcobject->un_pager.swp.swp_blocks = NULL;
	}
	return;
}

static void
swap_pager_dealloc(object)
	vm_object_t object;
{
	int s;
	sw_blk_t swb;

	/*
	 * Remove from list right away so lookups will fail if we block for
	 * pageout completion.
	 */
	if (object->handle == NULL) {
		TAILQ_REMOVE(&swap_pager_un_object_list, object, pager_object_list);
	} else {
		TAILQ_REMOVE(&swap_pager_object_list, object, pager_object_list);
	}

	/*
	 * Wait for all pageouts to finish and remove all entries from
	 * cleaning list.
	 */

	s = splvm();
	while (object->un_pager.swp.swp_poip) {
		tsleep(object, PVM, "swpout", 0);
	}
	splx(s);

	if (swap_pager_free_pending)
		swap_pager_sync();

	/*
	 * Free left over swap blocks
	 */
	swap_pager_free_swap(object);

	if (object->un_pager.swp.swp_allocsize) {
		printf("swap_pager_dealloc: *warning* freeing pager with %d blocks\n",
		    object->un_pager.swp.swp_allocsize);
	}
	swb = object->un_pager.swp.swp_blocks;
	if (swb) {
		/*
   		* Free swap management resources
   		*/
		free(swb, M_VMPGDATA);
		object->un_pager.swp.swp_blocks = NULL;
	}
}

static __inline int
swap_pager_block_index(pindex)
	vm_pindex_t pindex;
{
	return (pindex / SWB_NPAGES);
}

static __inline int
swap_pager_block_offset(pindex)
	vm_pindex_t pindex;
{
	return (pindex % SWB_NPAGES);
}

/*
 * swap_pager_haspage returns TRUE if the pager has data that has
 * been written out.
 */
static boolean_t
swap_pager_haspage(object, pindex, before, after)
	vm_object_t object;
	vm_pindex_t pindex;
	int *before;
	int *after;
{
	register sw_blk_t swb;
	int ix;

	if (before != NULL)
		*before = 0;
	if (after != NULL)
		*after = 0;
	ix = pindex / SWB_NPAGES;
	if (ix >= object->un_pager.swp.swp_nblocks) {
		return (FALSE);
	}
	swb = &object->un_pager.swp.swp_blocks[ix];
	ix = pindex % SWB_NPAGES;

	if (swb->swb_block[ix] != SWB_EMPTY) {

		if (swb->swb_valid & (1 << ix)) {
			int tix;
			if (before) {
				for(tix = ix - 1; tix >= 0; --tix) {
					if ((swb->swb_valid & (1 << tix)) == 0)
						break;
					if ((swb->swb_block[tix] +
						(ix - tix) * (PAGE_SIZE/DEV_BSIZE)) !=
						swb->swb_block[ix])
						break;
					(*before)++;
				}
			}

			if (after) {
				for(tix = ix + 1; tix < SWB_NPAGES; tix++) {
					if ((swb->swb_valid & (1 << tix)) == 0)
						break;
					if ((swb->swb_block[tix] -
						(tix - ix) * (PAGE_SIZE/DEV_BSIZE)) !=
						swb->swb_block[ix])
						break;
					(*after)++;
				}
			}

			return TRUE;
		}
	}
	return (FALSE);
}

/*
 * Wakeup based upon spc state
 */
static void
spc_wakeup(void)
{
	if( swap_pager_needflags & SWAP_FREE_NEEDED_BY_PAGEOUT) {
		swap_pager_needflags &= ~SWAP_FREE_NEEDED_BY_PAGEOUT;
		wakeup(&swap_pager_needflags);
	} else if ((swap_pager_needflags & SWAP_FREE_NEEDED) &&
		swap_pager_free_count >= ((2 * npendingio) / 3)) {
		swap_pager_needflags &= ~SWAP_FREE_NEEDED;
		wakeup(&swap_pager_free);
	}
}

/*
 * Free an spc structure
 */
static void
spc_free(spc)
	swp_clean_t spc;
{
	spc->spc_flags = 0;
	TAILQ_INSERT_TAIL(&swap_pager_free, spc, spc_list);
	swap_pager_free_count++;
	if (swap_pager_needflags) {
		spc_wakeup();
	}
}

/*
 * swap_pager_ridpages is a convienience routine that deallocates all
 * but the required page.  this is usually used in error returns that
 * need to invalidate the "extra" readahead pages.
 */
static void
swap_pager_ridpages(m, count, reqpage)
	vm_page_t *m;
	int count;
	int reqpage;
{
	int i;

	for (i = 0; i < count; i++) {
		if (i != reqpage) {
			vm_page_free(m[i]);
		}
	}
}

/*
 * swap_pager_iodone1 is the completion routine for both reads and async writes
 */
static void
swap_pager_iodone1(bp)
	struct buf *bp;
{
	bp->b_flags |= B_DONE;
	bp->b_flags &= ~B_ASYNC;
	wakeup(bp);
}

static int
swap_pager_getpages(object, m, count, reqpage)
	vm_object_t object;
	vm_page_t *m;
	int count, reqpage;
{
	register struct buf *bp;
	sw_blk_t swb[count];
	register int s;
	int i;
	boolean_t rv;
	vm_offset_t kva, off[count];
	vm_pindex_t paging_offset;
	int reqaddr[count];
	int sequential;

	int first, last;
	int failed;
	int reqdskregion;

	object = m[reqpage]->object;
	paging_offset = OFF_TO_IDX(object->paging_offset);
	sequential = (m[reqpage]->pindex == (object->last_read + 1));

	for (i = 0; i < count; i++) {
		vm_pindex_t fidx = m[i]->pindex + paging_offset;
		int ix = swap_pager_block_index(fidx);

		if (ix >= object->un_pager.swp.swp_nblocks) {
			int j;

			if (i <= reqpage) {
				swap_pager_ridpages(m, count, reqpage);
				return (VM_PAGER_FAIL);
			}
			for (j = i; j < count; j++) {
				vm_page_free(m[j]);
			}
			count = i;
			break;
		}
		swb[i] = &object->un_pager.swp.swp_blocks[ix];
		off[i] = swap_pager_block_offset(fidx);
		reqaddr[i] = swb[i]->swb_block[off[i]];
	}

	/* make sure that our required input request is existant */

	if (reqaddr[reqpage] == SWB_EMPTY ||
	    (swb[reqpage]->swb_valid & (1 << off[reqpage])) == 0) {
		swap_pager_ridpages(m, count, reqpage);
		return (VM_PAGER_FAIL);
	}
	reqdskregion = reqaddr[reqpage] / dmmax;

	/*
	 * search backwards for the first contiguous page to transfer
	 */
	failed = 0;
	first = 0;
	for (i = reqpage - 1; i >= 0; --i) {
		if (sequential || failed || (reqaddr[i] == SWB_EMPTY) ||
		    (swb[i]->swb_valid & (1 << off[i])) == 0 ||
		    (reqaddr[i] != (reqaddr[reqpage] + (i - reqpage) * btodb(PAGE_SIZE))) ||
		    ((reqaddr[i] / dmmax) != reqdskregion)) {
			failed = 1;
			vm_page_free(m[i]);
			if (first == 0)
				first = i + 1;
		}
	}
	/*
	 * search forwards for the last contiguous page to transfer
	 */
	failed = 0;
	last = count;
	for (i = reqpage + 1; i < count; i++) {
		if (failed || (reqaddr[i] == SWB_EMPTY) ||
		    (swb[i]->swb_valid & (1 << off[i])) == 0 ||
		    (reqaddr[i] != (reqaddr[reqpage] + (i - reqpage) * btodb(PAGE_SIZE))) ||
		    ((reqaddr[i] / dmmax) != reqdskregion)) {
			failed = 1;
			vm_page_free(m[i]);
			if (last == count)
				last = i;
		}
	}

	count = last;
	if (first != 0) {
		for (i = first; i < count; i++) {
			m[i - first] = m[i];
			reqaddr[i - first] = reqaddr[i];
			off[i - first] = off[i];
		}
		count -= first;
		reqpage -= first;
	}
	++swb[reqpage]->swb_locked;

	/*
	 * at this point: "m" is a pointer to the array of vm_page_t for
	 * paging I/O "count" is the number of vm_page_t entries represented
	 * by "m" "object" is the vm_object_t for I/O "reqpage" is the index
	 * into "m" for the page actually faulted
	 */

	/*
	 * Get a swap buffer header to perform the IO
	 */
	bp = getpbuf();
	kva = (vm_offset_t) bp->b_data;

	/*
	 * map our page(s) into kva for input
	 */
	pmap_qenter(kva, m, count);

	bp->b_flags = B_BUSY | B_READ | B_CALL | B_PAGING;
	bp->b_iodone = swap_pager_iodone1;
	bp->b_proc = &proc0;	/* XXX (but without B_PHYS set this is ok) */
	bp->b_rcred = bp->b_wcred = bp->b_proc->p_ucred;
	crhold(bp->b_rcred);
	crhold(bp->b_wcred);
	bp->b_data = (caddr_t) kva;
	bp->b_blkno = reqaddr[0];
	bp->b_bcount = PAGE_SIZE * count;
	bp->b_bufsize = PAGE_SIZE * count;

	pbgetvp(swapdev_vp, bp);

	cnt.v_swapin++;
	cnt.v_swappgsin += count;
	/*
	 * perform the I/O
	 */
	VOP_STRATEGY(bp);

	/*
	 * wait for the sync I/O to complete
	 */
	s = splvm();
	while ((bp->b_flags & B_DONE) == 0) {
		if (tsleep(bp, PVM, "swread", hz*20)) {
			printf("swap_pager: indefinite wait buffer: device: %#x, blkno: %d, size: %d\n",
				bp->b_dev, bp->b_blkno, bp->b_bcount);
		}
	}

	if (bp->b_flags & B_ERROR) {
		printf("swap_pager: I/O error - pagein failed; blkno %d, size %d, error %d\n",
		    bp->b_blkno, bp->b_bcount, bp->b_error);
		rv = VM_PAGER_ERROR;
	} else {
		rv = VM_PAGER_OK;
	}

	splx(s);
	swb[reqpage]->swb_locked--;

	/*
	 * remove the mapping for kernel virtual
	 */
	pmap_qremove(kva, count);

	/*
	 * release the physical I/O buffer
	 */
	relpbuf(bp);
	/*
	 * finish up input if everything is ok
	 */
	if (rv == VM_PAGER_OK) {
		for (i = 0; i < count; i++) {
			m[i]->dirty = 0;
			m[i]->flags &= ~PG_ZERO;
			if (i != reqpage) {
				/*
				 * whether or not to leave the page
				 * activated is up in the air, but we
				 * should put the page on a page queue
				 * somewhere. (it already is in the
				 * object). After some emperical
				 * results, it is best to deactivate
				 * the readahead pages.
				 */
				vm_page_deactivate(m[i]);

				/*
				 * just in case someone was asking for
				 * this page we now tell them that it
				 * is ok to use
				 */
				m[i]->valid = VM_PAGE_BITS_ALL;
				PAGE_WAKEUP(m[i]);
			}
		}

		m[reqpage]->object->last_read = m[count-1]->pindex;

		/*
		 * If we're out of swap space, then attempt to free
		 * some whenever multiple pages are brought in. We
		 * must set the dirty bits so that the page contents
		 * will be preserved.
		 */
		if (SWAPLOW ||
			(vm_swap_size < btodb((cnt.v_page_count - cnt.v_wire_count)) * PAGE_SIZE)) {
			for (i = 0; i < count; i++) {
				m[i]->dirty = VM_PAGE_BITS_ALL;
			}
			swap_pager_freespace(object,
				m[0]->pindex + paging_offset, count);
		}

	} else {
		swap_pager_ridpages(m, count, reqpage);
	}
	return (rv);
}

int
swap_pager_putpages(object, m, count, sync, rtvals)
	vm_object_t object;
	vm_page_t *m;
	int count;
	boolean_t sync;
	int *rtvals;
{
	register struct buf *bp;
	sw_blk_t swb[count];
	register int s;
	int i, j, ix, firstidx, lastidx;
	boolean_t rv;
	vm_offset_t kva, off, fidx;
	swp_clean_t spc;
	vm_pindex_t paging_pindex;
	int reqaddr[count];
	int failed;

	if (vm_swap_size)
		no_swap_space = 0;

	if (no_swap_space) {
		for (i = 0; i < count; i++)
			rtvals[i] = VM_PAGER_FAIL;
		return VM_PAGER_FAIL;
	}

	if (curproc != pageproc)
		sync = TRUE;

	object = m[0]->object;
	paging_pindex = OFF_TO_IDX(object->paging_offset);

	failed = 0;
	for (j = 0; j < count; j++) {
		fidx = m[j]->pindex + paging_pindex;
		ix = swap_pager_block_index(fidx);
		swb[j] = 0;
		if (ix >= object->un_pager.swp.swp_nblocks) {
			rtvals[j] = VM_PAGER_FAIL;
			failed = 1;
			continue;
		} else {
			rtvals[j] = VM_PAGER_OK;
		}
		swb[j] = &object->un_pager.swp.swp_blocks[ix];
		swb[j]->swb_locked++;
		if (failed) {
			rtvals[j] = VM_PAGER_FAIL;
			continue;
		}
		off = swap_pager_block_offset(fidx);
		reqaddr[j] = swb[j]->swb_block[off];
		if (reqaddr[j] == SWB_EMPTY) {
			daddr_t blk;
			int tries;
			int ntoget;

			tries = 0;
			s = splvm();

			/*
			 * if any other pages have been allocated in this
			 * block, we only try to get one page.
			 */
			for (i = 0; i < SWB_NPAGES; i++) {
				if (swb[j]->swb_block[i] != SWB_EMPTY)
					break;
			}

			ntoget = (i == SWB_NPAGES) ? SWB_NPAGES : 1;
			/*
			 * this code is alittle conservative, but works (the
			 * intent of this code is to allocate small chunks for
			 * small objects)
			 */
			if ((off == 0) && ((fidx + ntoget) > object->size)) {
				ntoget = object->size - fidx;
			}
	retrygetspace:
			if (!swap_pager_full && ntoget > 1 &&
			    swap_pager_getswapspace(object, ntoget * btodb(PAGE_SIZE),
				&blk)) {

				for (i = 0; i < ntoget; i++) {
					swb[j]->swb_block[i] = blk + btodb(PAGE_SIZE) * i;
					swb[j]->swb_valid = 0;
				}

				reqaddr[j] = swb[j]->swb_block[off];
			} else if (!swap_pager_getswapspace(object, btodb(PAGE_SIZE),
				&swb[j]->swb_block[off])) {
				/*
				 * if the allocation has failed, we try to
				 * reclaim space and retry.
				 */
				if (++tries == 1) {
					swap_pager_reclaim();
					goto retrygetspace;
				}
				rtvals[j] = VM_PAGER_AGAIN;
				failed = 1;
				swap_pager_full = 1;
			} else {
				reqaddr[j] = swb[j]->swb_block[off];
				swb[j]->swb_valid &= ~(1 << off);
			}
			splx(s);
		}
	}

	/*
	 * search forwards for the last contiguous page to transfer
	 */
	failed = 0;
	for (i = 0; i < count; i++) {
		if (failed ||
			(reqaddr[i] != reqaddr[0] + i * btodb(PAGE_SIZE)) ||
		    ((reqaddr[i] / dmmax) != (reqaddr[0] / dmmax)) ||
		    (rtvals[i] != VM_PAGER_OK)) {
			failed = 1;
			if (rtvals[i] == VM_PAGER_OK)
				rtvals[i] = VM_PAGER_AGAIN;
		}
	}

	ix = 0;
	firstidx = -1;
	for (i = 0; i < count; i++) {
		if (rtvals[i] == VM_PAGER_OK) {
			ix++;
			if (firstidx == -1) {
				firstidx = i;
			}
		} else if (firstidx >= 0) {
			break;
		}
	}

	if (firstidx == -1) {
		for (i = 0; i < count; i++) {
			if (rtvals[i] == VM_PAGER_OK)
				rtvals[i] = VM_PAGER_AGAIN;
		}
		return VM_PAGER_AGAIN;
	}

	lastidx = firstidx + ix;

	if (ix > max_pageout_cluster) {
		for (i = firstidx + max_pageout_cluster; i < lastidx; i++) {
			if (rtvals[i] == VM_PAGER_OK)
				rtvals[i] = VM_PAGER_AGAIN;
		}
		ix = max_pageout_cluster;
		lastidx = firstidx + ix;
	}

	for (i = 0; i < firstidx; i++) {
		if (swb[i])
			swb[i]->swb_locked--;
	}

	for (i = lastidx; i < count; i++) {
		if (swb[i])
			swb[i]->swb_locked--;
	}

#if defined(DIAGNOSTIC)
	for (i = firstidx; i < lastidx; i++) {
		if (reqaddr[i] == SWB_EMPTY) {
			printf("I/O to empty block???? -- pindex: %d, i: %d\n",
				m[i]->pindex, i);
		}
	}
#endif

	/*
	 * Clean up all completed async pageouts.
	 */
	if (swap_pager_free_pending)
		swap_pager_sync();

	/*
	 * get a swap pager clean data structure, block until we get it
	 */
	if (curproc == pageproc) {
		if (swap_pager_free_count == 0) {
			s = splvm();
			while (swap_pager_free_count == 0) {
				swap_pager_needflags |= SWAP_FREE_NEEDED_BY_PAGEOUT;
			/*
			 * if it does not get one within a short time, then
			 * there is a potential deadlock, so we go-on trying
			 * to free pages.  It is important to block here as opposed
			 * to returning, thereby allowing the pageout daemon to continue.
			 * It is likely that pageout daemon will start suboptimally
			 * reclaiming vnode backed pages if we don't block.  Since the
			 * I/O subsystem is probably already fully utilized, might as
			 * well wait.
			 */
				if (tsleep(&swap_pager_needflags, PVM-1, "swpfre", hz/2)) {
					if (swap_pager_free_pending)
						swap_pager_sync();
					if (swap_pager_free_count == 0) {
						for (i = firstidx; i < lastidx; i++) {
							rtvals[i] = VM_PAGER_AGAIN;
						}
						splx(s);
						return VM_PAGER_AGAIN;
					}
				} else {
					swap_pager_sync();
				}
			}
			splx(s);
		}

		spc = TAILQ_FIRST(&swap_pager_free);
#if defined(DIAGNOSTIC)
		if (spc == NULL)
			panic("swap_pager_putpages: free queue is empty, %d expected\n",
				swap_pager_free_count);
#endif
		TAILQ_REMOVE(&swap_pager_free, spc, spc_list);
		swap_pager_free_count--;

		kva = spc->spc_kva;
		bp = spc->spc_bp;
		bzero(bp, sizeof *bp);
		bp->b_spc = spc;
		bp->b_vnbufs.le_next = NOLIST;
		bp->b_data = (caddr_t) kva;
	} else {
		spc = NULL;
		bp = getpbuf();
		kva = (vm_offset_t) bp->b_data;
		bp->b_spc = NULL;
	}

	/*
	 * map our page(s) into kva for I/O
	 */
	pmap_qenter(kva, &m[firstidx], ix);

	/*
	 * get the base I/O offset into the swap file
	 */
	for (i = firstidx; i < lastidx ; i++) {
		fidx = m[i]->pindex + paging_pindex;
		off = swap_pager_block_offset(fidx);
		/*
		 * set the valid bit
		 */
		swb[i]->swb_valid |= (1 << off);
		/*
		 * and unlock the data structure
		 */
		swb[i]->swb_locked--;
	}

	bp->b_flags = B_BUSY | B_PAGING;
	bp->b_proc = &proc0;	/* XXX (but without B_PHYS set this is ok) */
	bp->b_rcred = bp->b_wcred = bp->b_proc->p_ucred;
	if (bp->b_rcred != NOCRED)
		crhold(bp->b_rcred);
	if (bp->b_wcred != NOCRED)
		crhold(bp->b_wcred);
	bp->b_blkno = reqaddr[firstidx];
	pbgetvp(swapdev_vp, bp);

	bp->b_bcount = PAGE_SIZE * ix;
	bp->b_bufsize = PAGE_SIZE * ix;

	s = splvm();
	swapdev_vp->v_numoutput++;

	/*
	 * If this is an async write we set up additional buffer fields and
  	 * place a "cleaning" entry on the inuse queue.
  	 */
 	object->un_pager.swp.swp_poip++;
 
 	if (spc) {
  		spc->spc_flags = 0;
  		spc->spc_object = object;
 		bp->b_npages = ix;
 		for (i = firstidx; i < lastidx; i++) {
  			spc->spc_m[i] = m[i];
 			bp->b_pages[i - firstidx] = m[i];
 			vm_page_protect(m[i], VM_PROT_READ);
 			pmap_clear_modify(VM_PAGE_TO_PHYS(m[i]));
 			m[i]->dirty = 0;
 		}
  		spc->spc_first = firstidx;
  		spc->spc_count = ix;
		/*
		 * the completion routine for async writes
		 */
		bp->b_flags |= B_CALL;
		bp->b_iodone = swap_pager_iodone;
		bp->b_dirtyoff = 0;
		bp->b_dirtyend = bp->b_bcount;
		TAILQ_INSERT_TAIL(&swap_pager_inuse, spc, spc_list);
	} else {
		bp->b_flags |= B_CALL;
		bp->b_iodone = swap_pager_iodone1;
		bp->b_npages = ix;
		for (i = firstidx; i < lastidx; i++)
			bp->b_pages[i - firstidx] = m[i];
	}

	cnt.v_swapout++;
	cnt.v_swappgsout += ix;

	/*
	 * perform the I/O
	 */
	VOP_STRATEGY(bp);
	if (sync == FALSE) {
		if (swap_pager_free_pending) {
			swap_pager_sync();
		}
		for (i = firstidx; i < lastidx; i++) {
			rtvals[i] = VM_PAGER_PEND;
		}
		return VM_PAGER_PEND;
	}

	s = splvm();
	/*
	 * wait for the sync I/O to complete
	 */
	while ((bp->b_flags & B_DONE) == 0) {
		tsleep(bp, PVM, "swwrt", 0);
	}

	if (bp->b_flags & B_ERROR) {
		printf("swap_pager: I/O error - pageout failed; blkno %d, size %d, error %d\n",
		    bp->b_blkno, bp->b_bcount, bp->b_error);
		rv = VM_PAGER_ERROR;
	} else {
		rv = VM_PAGER_OK;
	}

	object->un_pager.swp.swp_poip--;
	if (object->un_pager.swp.swp_poip == 0)
		wakeup(object);

	if (bp->b_vp)
		pbrelvp(bp);

	splx(s);

	/*
	 * remove the mapping for kernel virtual
	 */
	pmap_qremove(kva, ix);

	/*
	 * if we have written the page, then indicate that the page is clean.
	 */
	if (rv == VM_PAGER_OK) {
		for (i = firstidx; i < lastidx; i++) {
			if (rtvals[i] == VM_PAGER_OK) {
				pmap_clear_modify(VM_PAGE_TO_PHYS(m[i]));
				m[i]->dirty = 0;
				/*
				 * optimization, if a page has been read
				 * during the pageout process, we activate it.
				 */
				if (((m[i]->flags & (PG_WANTED|PG_REFERENCED)) ||
				    pmap_ts_referenced(VM_PAGE_TO_PHYS(m[i])))) {
					vm_page_activate(m[i]);
				}
			}
		}
	} else {
		for (i = firstidx; i < lastidx; i++) {
			rtvals[i] = rv;
		}
	}

	if (bp->b_rcred != NOCRED)
		crfree(bp->b_rcred);
	if (bp->b_wcred != NOCRED)
		crfree(bp->b_wcred);

	spc_free(spc);
	if (swap_pager_free_pending)
		swap_pager_sync();

	return (rv);
}

void
swap_pager_sync()
{
	swp_clean_t spc;

	while (spc = TAILQ_FIRST(&swap_pager_done)) {
		swap_pager_finish(spc);
	}
	return;
}

static void
swap_pager_finish(spc)
	register swp_clean_t spc;
{
	int i, s, lastidx;
	vm_object_t object;
	vm_page_t *ma;

	ma = spc->spc_m;
	object = spc->spc_object;
	lastidx = spc->spc_first + spc->spc_count;

	s = splvm();
	TAILQ_REMOVE(&swap_pager_done, spc, spc_list);
	splx(s);

	pmap_qremove(spc->spc_kva, spc->spc_count);

	/*
	 * If no error, mark as clean and inform the pmap system. If error,
	 * mark as dirty so we will try again. (XXX could get stuck doing
	 * this, should give up after awhile)
	 */
	if (spc->spc_flags & SPC_ERROR) {

		for (i = spc->spc_first; i < lastidx; i++) {
			printf("swap_pager_finish: I/O error, clean of page %lx failed\n",
			    (u_long) VM_PAGE_TO_PHYS(ma[i]));
			ma[i]->dirty = VM_PAGE_BITS_ALL;
			PAGE_BWAKEUP(ma[i]);
		}

		object->paging_in_progress -= spc->spc_count;
		if ((object->paging_in_progress == 0) &&
			(object->flags & OBJ_PIPWNT)) {
			object->flags &= ~OBJ_PIPWNT;
			wakeup(object);
		}

	} else {
		for (i = spc->spc_first; i < lastidx; i++) {
			if ((ma[i]->queue != PQ_ACTIVE) &&
			   ((ma[i]->flags & PG_WANTED) ||
				 pmap_ts_referenced(VM_PAGE_TO_PHYS(ma[i])))) {
				vm_page_activate(ma[i]);
			}
		}
	}

	nswiodone -= spc->spc_count;
	swap_pager_free_pending--;
	spc_free(spc);

	return;
}

/*
 * swap_pager_iodone
 */
static void
swap_pager_iodone(bp)
	register struct buf *bp;
{
	int i, s, lastidx;
	register swp_clean_t spc;
	vm_object_t object;
	vm_page_t *ma;


	s = splvm();
	spc = (swp_clean_t) bp->b_spc;
	TAILQ_REMOVE(&swap_pager_inuse, spc, spc_list);
	TAILQ_INSERT_TAIL(&swap_pager_done, spc, spc_list);

	object = spc->spc_object;

#if defined(DIAGNOSTIC)
	if (object->paging_in_progress < spc->spc_count)
		printf("swap_pager_iodone: paging_in_progress(%d) < spc_count(%d)\n",
			object->paging_in_progress, spc->spc_count);
#endif

	if (bp->b_flags & B_ERROR) {
		spc->spc_flags |= SPC_ERROR;
		printf("swap_pager: I/O error - async %s failed; blkno %lu, size %ld, error %d\n",
		    (bp->b_flags & B_READ) ? "pagein" : "pageout",
		    (u_long) bp->b_blkno, bp->b_bcount, bp->b_error);
	} else {
		object->paging_in_progress -= spc->spc_count;
		if ((object->paging_in_progress == 0) &&
			(object->flags & OBJ_PIPWNT)) {
			object->flags &= ~OBJ_PIPWNT;
			wakeup(object);
		}
		ma = spc->spc_m;
		lastidx = spc->spc_first + spc->spc_count;
		for (i = spc->spc_first; i < lastidx; i++) {
			/*
			 * we wakeup any processes that are waiting on these pages.
			 */
			PAGE_BWAKEUP(ma[i]);
		}
	}

	if (bp->b_vp)
		pbrelvp(bp);

	if (bp->b_rcred != NOCRED)
		crfree(bp->b_rcred);
	if (bp->b_wcred != NOCRED)
		crfree(bp->b_wcred);

	nswiodone += spc->spc_count;
	swap_pager_free_pending++;
	if (--spc->spc_object->un_pager.swp.swp_poip == 0) {
		wakeup(spc->spc_object);
	}

	if (swap_pager_needflags &&
	  ((swap_pager_free_count + swap_pager_free_pending) > (npendingio / 2))) {
		spc_wakeup();
	}

	if ((TAILQ_FIRST(&swap_pager_inuse) == NULL) &&
		vm_pageout_pages_needed) {
		wakeup(&vm_pageout_pages_needed);
		vm_pageout_pages_needed = 0;
	}

	splx(s);
}