freebsd-skq/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
 * $Id$
 */

/*
 * 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/proc.h>
#include <sys/buf.h>
#include <sys/vnode.h>
#include <sys/malloc.h>

#include <miscfs/specfs/specdev.h>
#include <sys/rlist.h>

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

#ifndef NPENDINGIO
#define NPENDINGIO	16
#endif

extern int nswbuf;
int nswiodone;
extern int vm_pageout_rate_limit;
static int cleandone;
extern int hz;
int swap_pager_full;
extern vm_map_t pager_map;
extern int vm_pageout_pages_needed;
extern int vm_swap_size;
extern struct vnode *swapdev_vp;

#define MAX_PAGEOUT_CLUSTER 8

TAILQ_HEAD(swpclean, swpagerclean);

typedef	struct swpagerclean	*swp_clean_t;

struct swpagerclean {
	TAILQ_ENTRY(swpagerclean)	spc_list;
	int				spc_flags;
	struct buf			*spc_bp;
	sw_pager_t			spc_swp;
	vm_offset_t			spc_kva;
	vm_offset_t			spc_altkva;
	int				spc_count;
	vm_page_t			spc_m[MAX_PAGEOUT_CLUSTER];
} swcleanlist [NPENDINGIO] ;


extern vm_map_t kernel_map;

/* spc_flags values */
#define SPC_ERROR	0x01

#define SWB_EMPTY (-1)

void		swap_pager_init(void);
vm_pager_t	swap_pager_alloc(caddr_t, vm_size_t, vm_prot_t, vm_offset_t);
void		swap_pager_dealloc(vm_pager_t);
boolean_t	swap_pager_getpage(vm_pager_t, vm_page_t, boolean_t);
boolean_t	swap_pager_putpage(vm_pager_t, vm_page_t, boolean_t);
boolean_t	swap_pager_getmulti(vm_pager_t, vm_page_t *, int, int, boolean_t);
boolean_t	swap_pager_haspage(vm_pager_t, vm_offset_t);
int		swap_pager_io(sw_pager_t, vm_page_t *, int, int, int);
void		swap_pager_iodone(struct buf *);
boolean_t	swap_pager_clean();

extern struct pagerops swappagerops;

struct swpclean swap_pager_done;	/* list of compileted page cleans */
struct swpclean swap_pager_inuse;	/* list of pending page cleans */
struct swpclean swap_pager_free;	/* list of free pager clean structs */
struct pagerlst swap_pager_list;	/* list of "named" anon regions */
struct pagerlst swap_pager_un_list;	/* list of "unnamed" anon pagers */

#define	SWAP_FREE_NEEDED	0x1	/* need a swap block */
int swap_pager_needflags;
struct rlist *swapfrag;

struct pagerlst *swp_qs[]={
	&swap_pager_list, &swap_pager_un_list, (struct pagerlst *) 0
};

int swap_pager_putmulti();

struct pagerops swappagerops = {
	swap_pager_init,
	swap_pager_alloc,
	swap_pager_dealloc,
	swap_pager_getpage,
	swap_pager_getmulti,
	swap_pager_putpage,
	swap_pager_putmulti,
	swap_pager_haspage
};

extern int nswbuf;

int npendingio = NPENDINGIO;
int pendingiowait;
int require_swap_init;
void swap_pager_finish();
int dmmin, dmmax;
extern int vm_page_count;

struct buf * getpbuf() ;
void relpbuf(struct buf *bp) ;

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

void
swap_pager_init()
{
	extern int dmmin, dmmax;

	dfltpagerops = &swappagerops;

	TAILQ_INIT(&swap_pager_list);
	TAILQ_INIT(&swap_pager_un_list);

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

	require_swap_init = 1;

	/*
	 * Calculate the swap allocation constants.
	 */

	dmmin = CLBYTES/DEV_BSIZE;
	dmmax = btodb(SWB_NPAGES*PAGE_SIZE)*2;

}

/*
 * Allocate a pager structure 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.
 */
vm_pager_t
swap_pager_alloc(handle, size, prot, offset)
	caddr_t handle;
	register vm_size_t size;
	vm_prot_t prot;
	vm_offset_t offset;
{
	register vm_pager_t pager;
	register sw_pager_t swp;
	int waitok;
	int i,j;
			
	if (require_swap_init) {
		swp_clean_t spc;
		struct buf *bp;
		/*
		 * 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);
			if (!spc->spc_kva) {
				break;
			}
			spc->spc_bp = malloc( sizeof( *bp), M_TEMP, M_NOWAIT);
			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);
		}
		require_swap_init = 0;
		if( size == 0)
			return(NULL);
	}
		
	/*
	 * If this is a "named" anonymous region, look it up and
	 * return the appropriate pager if it exists.
	 */
	if (handle) {
		pager = vm_pager_lookup(&swap_pager_list, handle);
		if (pager != NULL) {
			/*
			 * Use vm_object_lookup to gain a reference
			 * to the object and also to remove from the
			 * object cache.
			 */
			if (vm_object_lookup(pager) == NULL)
				panic("swap_pager_alloc: bad object");
			return(pager);
		}
	}

	if (swap_pager_full) {
		return(NULL);
	}

	/*
	 * Pager doesn't exist, allocate swap management resources
	 * and initialize.
	 */
	waitok = handle ? M_WAITOK : M_NOWAIT; 
	pager = (vm_pager_t)malloc(sizeof *pager, M_VMPAGER, waitok);
	if (pager == NULL)
		return(NULL);
	swp = (sw_pager_t)malloc(sizeof *swp, M_VMPGDATA, waitok);
	if (swp == NULL) {
		free((caddr_t)pager, M_VMPAGER);
		return(NULL);
	}
	size = round_page(size);
	swp->sw_osize = size;
	swp->sw_nblocks = (btodb(size) + btodb(SWB_NPAGES * PAGE_SIZE) - 1) / btodb(SWB_NPAGES*PAGE_SIZE);
	swp->sw_blocks = (sw_blk_t)
		malloc(swp->sw_nblocks*sizeof(*swp->sw_blocks),
		       M_VMPGDATA, waitok);
	if (swp->sw_blocks == NULL) {
		free((caddr_t)swp, M_VMPGDATA);
		free((caddr_t)pager, M_VMPAGER);
		return(NULL);
	}

	for (i = 0; i < swp->sw_nblocks; i++) {
		swp->sw_blocks[i].swb_valid = 0;
		swp->sw_blocks[i].swb_locked = 0;
		for (j = 0; j < SWB_NPAGES; j++)
			swp->sw_blocks[i].swb_block[j] = SWB_EMPTY;
	}

	swp->sw_poip = 0;
	if (handle) {
		vm_object_t object;

		swp->sw_flags = SW_NAMED;
		TAILQ_INSERT_TAIL(&swap_pager_list, pager, pg_list);
		/*
		 * Consistant with other pagers: return with object
		 * referenced.  Can't do this with handle == NULL
		 * since it might be the pageout daemon calling.
		 */
		object = vm_object_allocate(size);
		vm_object_enter(object, pager);
		vm_object_setpager(object, pager, 0, FALSE);
	} else {
		swp->sw_flags = 0;
		TAILQ_INSERT_TAIL(&swap_pager_un_list, pager, pg_list);
	}
	pager->pg_handle = handle;
	pager->pg_ops = &swappagerops;
	pager->pg_type = PG_SWAP;
	pager->pg_data = (caddr_t)swp;

	return(pager);
}

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

static int *
swap_pager_diskaddr(swp, offset, valid)
	sw_pager_t swp;
	vm_offset_t offset;
	int *valid;
{
	register sw_blk_t swb;
	int ix;

	if (valid)
		*valid = 0;
	ix = offset / (SWB_NPAGES*PAGE_SIZE);
	if (swp->sw_blocks == NULL || ix >= swp->sw_nblocks) {
		return(FALSE);
	}
	swb = &swp->sw_blocks[ix];
	ix = (offset % (SWB_NPAGES*PAGE_SIZE)) / PAGE_SIZE;
	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(swp, offset, valid)
	sw_pager_t swp;
	vm_offset_t offset;
	int valid;
{
	register sw_blk_t swb;
	int ix;
	
	ix = offset / (SWB_NPAGES*PAGE_SIZE);
	if (swp->sw_blocks == NULL || ix >= swp->sw_nblocks) 
		return;

	swb = &swp->sw_blocks[ix];
	ix = (offset % (SWB_NPAGES*PAGE_SIZE)) / PAGE_SIZE;
	if (valid)
		swb->swb_valid |= (1 << ix);
	else
		swb->swb_valid &= ~(1 << ix);
	return;
}

/*
 * this routine allocates swap space with a fragmentation
 * minimization policy.
 */
int
swap_pager_getswapspace( unsigned amount, unsigned *rtval) {
	unsigned tmpalloc;
	unsigned nblocksfrag = btodb(SWB_NPAGES*PAGE_SIZE);
	if( amount < nblocksfrag) {
		if( rlist_alloc(&swapfrag, amount, rtval))
			return 1;
		if( !rlist_alloc(&swapmap, nblocksfrag, &tmpalloc))
			return 0;
		rlist_free( &swapfrag, tmpalloc+amount, tmpalloc + nblocksfrag - 1);
		*rtval = tmpalloc;
		return 1;
	}
	if( !rlist_alloc(&swapmap, amount, rtval))
		return 0;
	else
		return 1;
}

/*
 * this routine frees swap space with a fragmentation
 * minimization policy.
 */
void
swap_pager_freeswapspace( unsigned from, unsigned to) {
	unsigned nblocksfrag = btodb(SWB_NPAGES*PAGE_SIZE);
	unsigned tmpalloc;
	if( ((to + 1) - from) >= nblocksfrag) {
		while( (from + nblocksfrag) <= to + 1) {
			rlist_free(&swapmap, from, from + nblocksfrag - 1);
			from += nblocksfrag;
		}
	}
	if( from >= to)
		return;
	rlist_free(&swapfrag, from, to);
	while( rlist_alloc(&swapfrag, nblocksfrag, &tmpalloc)) {
		rlist_free(&swapmap, tmpalloc, tmpalloc + nblocksfrag-1);
	}
}
/*
 * this routine frees swap blocks from a specified pager
 */
void
_swap_pager_freespace(swp, start, size)
	sw_pager_t swp;
	vm_offset_t start;
	vm_offset_t size;
{
	vm_offset_t i;
	int s;

	s = splbio();
	for (i = start; i < round_page(start + size - 1); i += PAGE_SIZE) {
		int valid;
		int *addr = swap_pager_diskaddr(swp, i, &valid);
		if (addr && *addr != SWB_EMPTY) {
			swap_pager_freeswapspace(*addr, *addr+btodb(PAGE_SIZE) - 1);
			if( valid) {
				vm_swap_size += btodb(PAGE_SIZE);
				swap_pager_setvalid(swp, i, 0);
			}
			*addr = SWB_EMPTY;
		}
	}
	swapsizecheck();
	splx(s);
}

void
swap_pager_freespace(pager, start, size) 
	vm_pager_t pager;
	vm_offset_t start;
	vm_offset_t size;
{
	_swap_pager_freespace((sw_pager_t) pager->pg_data, start, size);
}
	
/*
 * 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 256

void
swap_pager_reclaim()
{
	vm_pager_t p;
	sw_pager_t swp;
	int i, j, k;
	int s;
	int reclaimcount;
	static int reclaims[MAXRECLAIM];
	static int in_reclaim;

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

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

		p = swp_qs[k]->tqh_first;
		while (p && (reclaimcount < MAXRECLAIM)) {

			/*
			 * see if any blocks associated with a pager has been
			 * allocated but not used (written)
			 */
			swp = (sw_pager_t) p->pg_data;
			for (i = 0; i < swp->sw_nblocks; i++) {
				sw_blk_t swb = &swp->sw_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++] = swb->swb_block[j];
						swb->swb_block[j] = SWB_EMPTY;
						if (reclaimcount >= MAXRECLAIM)
							goto rfinished;
					}
				}
			}
			p = p->pg_list.tqe_next;
		}
	}
	
rfinished:

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

	splx(s);
	in_reclaim = 0;
	wakeup((caddr_t) &in_reclaim);
}
		

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

void
swap_pager_copy(srcpager, srcoffset, dstpager, dstoffset, offset)
	vm_pager_t srcpager;
	vm_offset_t srcoffset;
	vm_pager_t dstpager;
	vm_offset_t dstoffset;
	vm_offset_t offset;
{
	sw_pager_t srcswp, dstswp;
	vm_offset_t i;
	int s;

	srcswp = (sw_pager_t) srcpager->pg_data;
	dstswp = (sw_pager_t) dstpager->pg_data;

/*
 * remove the source pager from the swap_pager internal queue
 */
	s = splbio();
	if (srcswp->sw_flags & SW_NAMED) {
		TAILQ_REMOVE(&swap_pager_list, srcpager, pg_list);
		srcswp->sw_flags &= ~SW_NAMED;
	} else {
		TAILQ_REMOVE(&swap_pager_un_list, srcpager, pg_list);
	}
	
	while (srcswp->sw_poip) {
		tsleep((caddr_t)srcswp, PVM, "spgout", 0); 
	}
	splx(s);

/*
 * clean all of the pages that are currently active and finished
 */
	(void) swap_pager_clean();
	
	s = splbio();
/*
 * clear source block before destination object
 * (release allocated space)
 */
	for (i = 0; i < offset + srcoffset; i += PAGE_SIZE) {
		int valid;
		int *addr = swap_pager_diskaddr(srcswp, i, &valid);
		if (addr && *addr != SWB_EMPTY) {
			swap_pager_freeswapspace(*addr, *addr+btodb(PAGE_SIZE) - 1);
			if( valid)
				vm_swap_size += btodb(PAGE_SIZE);
			swapsizecheck();
			*addr = SWB_EMPTY;
		}
	}
/*
 * transfer source to destination
 */
	for (i = 0; i < dstswp->sw_osize; i += PAGE_SIZE) {
		int srcvalid, dstvalid;
		int *srcaddrp = swap_pager_diskaddr(srcswp, i + offset + srcoffset,
			&srcvalid);
		int *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(dstswp, 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(*dstaddrp, *dstaddrp+btodb(PAGE_SIZE) - 1);
					*dstaddrp = SWB_EMPTY;
				}
				if (dstaddrp && *dstaddrp == SWB_EMPTY) {
					*dstaddrp = *srcaddrp;
					*srcaddrp = SWB_EMPTY;
					swap_pager_setvalid(dstswp, i + dstoffset, 1);
					vm_swap_size -= btodb(PAGE_SIZE);
				} 
			} 
		/*
		 * if the source is not empty at this point, then deallocate the space.
		 */
			if (*srcaddrp != SWB_EMPTY) {
				swap_pager_freeswapspace(*srcaddrp, *srcaddrp+btodb(PAGE_SIZE) - 1);
				if( srcvalid)
					vm_swap_size += btodb(PAGE_SIZE);
				*srcaddrp = SWB_EMPTY;
			}
		}
	}

/*
 * deallocate the rest of the source object
 */
	for (i = dstswp->sw_osize + offset + srcoffset; i < srcswp->sw_osize; i += PAGE_SIZE) {
		int valid;
		int *srcaddrp = swap_pager_diskaddr(srcswp, i, &valid);
		if (srcaddrp && *srcaddrp != SWB_EMPTY) {
			swap_pager_freeswapspace(*srcaddrp, *srcaddrp+btodb(PAGE_SIZE) - 1);
			if( valid)
				vm_swap_size += btodb(PAGE_SIZE);
			*srcaddrp = SWB_EMPTY;
		}
	}
				
	swapsizecheck();
	splx(s);

	free((caddr_t)srcswp->sw_blocks, M_VMPGDATA);
	srcswp->sw_blocks = 0;
	free((caddr_t)srcswp, M_VMPGDATA);
	srcpager->pg_data = 0;
	free((caddr_t)srcpager, M_VMPAGER);

	return;
}


void
swap_pager_dealloc(pager)
	vm_pager_t pager;
{
	register int i,j;
	register sw_blk_t bp;
	register sw_pager_t swp;
	int s;

	/*
	 * Remove from list right away so lookups will fail if we
	 * block for pageout completion.
	 */
	s = splbio();
	swp = (sw_pager_t) pager->pg_data;
	if (swp->sw_flags & SW_NAMED) {
		TAILQ_REMOVE(&swap_pager_list, pager, pg_list);
		swp->sw_flags &= ~SW_NAMED;
	} else {
		TAILQ_REMOVE(&swap_pager_un_list, pager, pg_list);
	}
	/*
	 * Wait for all pageouts to finish and remove
	 * all entries from cleaning list.
	 */

	while (swp->sw_poip) {
		tsleep((caddr_t)swp, PVM, "swpout", 0); 
	}
	splx(s);
		

	(void) swap_pager_clean();

	/*
	 * Free left over swap blocks
	 */
	s = splbio();
	for (i = 0, bp = swp->sw_blocks; i < swp->sw_nblocks; i++, bp++) {
		for (j = 0; j < SWB_NPAGES; j++)
		if (bp->swb_block[j] != SWB_EMPTY) {
			swap_pager_freeswapspace((unsigned)bp->swb_block[j],
				(unsigned)bp->swb_block[j] + btodb(PAGE_SIZE) - 1);
			if( bp->swb_valid & (1<<j))
				vm_swap_size += btodb(PAGE_SIZE);
			bp->swb_block[j] = SWB_EMPTY;
		}
	}
	splx(s);
	swapsizecheck();

	/*
	 * Free swap management resources
	 */
	free((caddr_t)swp->sw_blocks, M_VMPGDATA);
	swp->sw_blocks = 0;
	free((caddr_t)swp, M_VMPGDATA);
	pager->pg_data = 0;
	free((caddr_t)pager, M_VMPAGER);
}

/*
 * swap_pager_getmulti can get multiple pages.
 */
int
swap_pager_getmulti(pager, m, count, reqpage, sync)
	vm_pager_t pager;
	vm_page_t *m;
	int count;
	int reqpage;
	boolean_t sync;
{
	if( reqpage >= count)
		panic("swap_pager_getmulti: reqpage >= count\n");
	return swap_pager_input((sw_pager_t) pager->pg_data, m, count, reqpage);
}

/*
 * swap_pager_getpage gets individual pages
 */
int
swap_pager_getpage(pager, m, sync)
	vm_pager_t pager;
	vm_page_t m;
	boolean_t sync;
{
	vm_page_t marray[1];
	
	marray[0] = m;
	return swap_pager_input((sw_pager_t)pager->pg_data, marray, 1, 0);
}

int
swap_pager_putmulti(pager, m, c, sync, rtvals)
	vm_pager_t pager;
	vm_page_t *m;
	int c;
	boolean_t sync;
	int *rtvals;
{
	int flags;

	if (pager == NULL) {
		(void) swap_pager_clean();
		return VM_PAGER_OK;
	}
	
	flags = B_WRITE;
	if (!sync)
		flags |= B_ASYNC;
	
	return swap_pager_output((sw_pager_t)pager->pg_data, m, c, flags, rtvals);
}

/*
 * swap_pager_putpage writes individual pages
 */
int
swap_pager_putpage(pager, m, sync)
	vm_pager_t pager;
	vm_page_t m;
	boolean_t sync;
{
	int flags;
	vm_page_t marray[1];
	int rtvals[1];


	if (pager == NULL) {
		(void) swap_pager_clean();
		return VM_PAGER_OK;
	}
	
	marray[0] = m;
	flags = B_WRITE;
	if (!sync)
		flags |= B_ASYNC;
	
	swap_pager_output((sw_pager_t)pager->pg_data, marray, 1, flags, rtvals);

	return rtvals[0];
}

static inline int
const swap_pager_block_index(swp, offset)
	sw_pager_t swp;
	vm_offset_t offset;
{
	return (offset / (SWB_NPAGES*PAGE_SIZE));
}

static inline int
const swap_pager_block_offset(swp, offset)
	sw_pager_t swp;
	vm_offset_t offset;
{	
	return ((offset % (PAGE_SIZE*SWB_NPAGES)) / PAGE_SIZE);
}

/*
 * _swap_pager_haspage returns TRUE if the pager has data that has
 * been written out.  
 */
static boolean_t
_swap_pager_haspage(swp, offset)
	sw_pager_t swp;
	vm_offset_t offset;
{
	register sw_blk_t swb;
	int ix;

	ix = offset / (SWB_NPAGES*PAGE_SIZE);
	if (swp->sw_blocks == NULL || ix >= swp->sw_nblocks) {
		return(FALSE);
	}
	swb = &swp->sw_blocks[ix];
	ix = (offset % (SWB_NPAGES*PAGE_SIZE)) / PAGE_SIZE;
	if (swb->swb_block[ix] != SWB_EMPTY) {
		if (swb->swb_valid & (1 << ix))
			return TRUE;
	}

	return(FALSE);
}

/*
 * swap_pager_haspage is the externally accessible version of
 * _swap_pager_haspage above.  this routine takes a vm_pager_t
 * for an argument instead of sw_pager_t.
 */
boolean_t
swap_pager_haspage(pager, offset)
	vm_pager_t pager;
	vm_offset_t offset;
{
	return _swap_pager_haspage((sw_pager_t) pager->pg_data, offset);
}

/*
 * swap_pager_freepage is a convienience routine that clears the busy
 * bit and deallocates a page.
 */
static void
swap_pager_freepage(m)
	vm_page_t m;
{
	PAGE_WAKEUP(m);
	vm_page_free(m);
}

/*
 * 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)
			swap_pager_freepage(m[i]);
}

int swapwritecount=0;

/*
 * swap_pager_iodone1 is the completion routine for both reads and async writes
 */
void
swap_pager_iodone1(bp)
	struct buf *bp;
{
	bp->b_flags |= B_DONE;
	bp->b_flags &= ~B_ASYNC;
	wakeup((caddr_t)bp);
/*
	if ((bp->b_flags & B_READ) == 0)
		vwakeup(bp);
*/
}


int
swap_pager_input(swp, m, count, reqpage)
	register sw_pager_t swp;
	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];
	swp_clean_t spc;
	vm_offset_t paging_offset;
	vm_object_t object;
	int reqaddr[count];

	int first, last;
	int failed;
	int reqdskregion;

	object = m[reqpage]->object;
	paging_offset = object->paging_offset;
	/*
	 * First determine if the page exists in the pager if this is
	 * a sync read.  This quickly handles cases where we are
	 * following shadow chains looking for the top level object
	 * with the page.
	 */
	if (swp->sw_blocks == NULL) {
		swap_pager_ridpages(m, count, reqpage);
		return(VM_PAGER_FAIL);
	}
		
	for(i = 0; i < count; i++) {
		vm_offset_t foff = m[i]->offset + paging_offset;
		int ix = swap_pager_block_index(swp, foff);
		if (ix >= swp->sw_nblocks) {
			int j;
			if( i <= reqpage) {
				swap_pager_ridpages(m, count, reqpage);
				return(VM_PAGER_FAIL);
			}
			for(j = i; j < count; j++) {
				swap_pager_freepage(m[j]);
			}
			count = i;
			break;
		}
	
		swb[i] = &swp->sw_blocks[ix];
		off[i] = swap_pager_block_offset(swp, foff);
		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 ( 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;
				swap_pager_freepage(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;
				swap_pager_freepage(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
	 */
	
	spc = NULL;	/* we might not use an spc data structure */
	kva = 0;

	/*
	 * we allocate a new kva for transfers > 1 page
	 * but for transfers == 1 page, the swap_pager_free list contains
	 * entries that have pre-allocated kva's (for efficiency).
	 */
	if (count > 1) {
		kva = kmem_alloc_pageable(pager_map, count*PAGE_SIZE);
	}


	if (!kva) {
		/*
		 * if a kva has not been allocated, we can only do a one page transfer,
		 * so we free the other pages that might have been allocated by
		 * vm_fault.
		 */
		swap_pager_ridpages(m, count, reqpage);
		m[0] = m[reqpage];
		reqaddr[0] = reqaddr[reqpage];

		count = 1;
		reqpage = 0;
	/*
	 * get a swap pager clean data structure, block until we get it
	 */
		if (swap_pager_free.tqh_first == NULL) {
			s = splbio();
			if( curproc == pageproc)
				(void) swap_pager_clean();
			else
				wakeup((caddr_t) &vm_pages_needed);
			while (swap_pager_free.tqh_first == NULL) { 
				swap_pager_needflags |= SWAP_FREE_NEEDED;
				tsleep((caddr_t)&swap_pager_free,
					PVM, "swpfre", 0);
				if( curproc == pageproc)
					(void) swap_pager_clean();
				else
					wakeup((caddr_t) &vm_pages_needed);
			}
			splx(s);
		}
		spc = swap_pager_free.tqh_first;
		TAILQ_REMOVE(&swap_pager_free, spc, spc_list);
		kva = spc->spc_kva;
	}
	

	/*
	 * map our page(s) into kva for input
	 */
	for (i = 0; i < count; i++) {
		pmap_kenter( kva + PAGE_SIZE * i, VM_PAGE_TO_PHYS(m[i]));
	}
	pmap_update();


	/*
	 * Get a swap buffer header and perform the IO
	 */
	if( spc) {
		bp = spc->spc_bp;
		bzero(bp, sizeof *bp);
		bp->b_spc = spc;
	} else {
		bp = getpbuf();
	}

	s = splbio();
	bp->b_flags = B_BUSY | B_READ | B_CALL;
	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_un.b_addr = (caddr_t) kva;
	bp->b_blkno = reqaddr[0];
	bp->b_bcount = PAGE_SIZE*count;
	bp->b_bufsize = PAGE_SIZE*count;

/*
	VHOLD(swapdev_vp);
	bp->b_vp = swapdev_vp;
	if (swapdev_vp->v_type == VBLK)
		bp->b_dev = swapdev_vp->v_rdev;
*/
	bgetvp( swapdev_vp, bp);

	swp->sw_piip++;

	/*
	 * perform the I/O
	 */
	VOP_STRATEGY(bp);

	/*
	 * wait for the sync I/O to complete
	 */
	while ((bp->b_flags & B_DONE) == 0) {
		tsleep((caddr_t)bp, PVM, "swread", 0);
	}
	rv = (bp->b_flags & B_ERROR) ? VM_PAGER_FAIL : VM_PAGER_OK;
	bp->b_flags &= ~(B_BUSY|B_WANTED|B_PHYS|B_DIRTY|B_CALL|B_DONE);

	--swp->sw_piip;
	if (swp->sw_piip == 0)
		wakeup((caddr_t) swp);
		
	/*
	 * relpbuf does this, but we maintain our own buffer
	 * list also...
	 */
	if (bp->b_vp)
		brelvp(bp);

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

	/*
	 * remove the mapping for kernel virtual
	 */
	pmap_remove(vm_map_pmap(pager_map), kva, kva + count * PAGE_SIZE);

	if (spc) {
		/*
		 * if we have used an spc, we need to free it.
		 */
		if( bp->b_rcred != NOCRED)
			crfree(bp->b_rcred);
		if( bp->b_wcred != NOCRED)
			crfree(bp->b_wcred);
		TAILQ_INSERT_TAIL(&swap_pager_free, spc, spc_list);
		if (swap_pager_needflags & SWAP_FREE_NEEDED) {
			swap_pager_needflags &= ~SWAP_FREE_NEEDED;
			wakeup((caddr_t)&swap_pager_free);
		}
	} else {
		/*
		 * free the kernel virtual addresses
		 */
		kmem_free_wakeup(pager_map, kva, count * PAGE_SIZE);
		/*
		 * 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++) {
				pmap_clear_modify(VM_PAGE_TO_PHYS(m[i]));
				m[i]->flags |= PG_CLEAN;
				m[i]->flags &= ~PG_LAUNDRY;
				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]->flags &= ~PG_FAKE;
					PAGE_WAKEUP(m[i]);
				}
			}
			if( swap_pager_full) {
				_swap_pager_freespace( swp, m[0]->offset+paging_offset, count*PAGE_SIZE);
			}
		} else {
			swap_pager_ridpages(m, count, reqpage);
		}
	}
	return(rv);
}

int
swap_pager_output(swp, m, count, flags, rtvals)
	register sw_pager_t swp;
	vm_page_t *m;
	int count;
	int flags;
	int *rtvals;
{
	register struct buf *bp;
	sw_blk_t swb[count];
	register int s;
	int i, j, ix;
	boolean_t rv;
	vm_offset_t kva, off, foff;
	swp_clean_t spc;
	vm_offset_t paging_offset;
	vm_object_t object;
	int reqaddr[count];
	int failed;

/*
	if( count > 1)
		printf("off: 0x%x, count: %d\n", m[0]->offset, count);
*/
	spc = NULL;

	object = m[0]->object;
	paging_offset = object->paging_offset;

	failed = 0;
	for(j=0;j<count;j++) {
		foff = m[j]->offset + paging_offset;
		ix = swap_pager_block_index(swp, foff);
		swb[j] = 0;
		if( swp->sw_blocks == NULL || ix >= swp->sw_nblocks) {
			rtvals[j] = VM_PAGER_FAIL;
			failed = 1;
			continue;
		} else {
			rtvals[j] = VM_PAGER_OK;
		}
		swb[j] = &swp->sw_blocks[ix];
		++swb[j]->swb_locked;
		if( failed) {
			rtvals[j] = VM_PAGER_FAIL;
			continue;
		}
		off = swap_pager_block_offset(swp, foff);
		reqaddr[j] = swb[j]->swb_block[off];
		if( reqaddr[j] == SWB_EMPTY) {
			int blk;
			int tries;
			int ntoget;
			tries = 0;
			s = splbio();

			/*
			 * 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( (m[j]->offset == 0) && (ntoget*PAGE_SIZE > object->size)) {
				ntoget = (object->size + (PAGE_SIZE-1))/PAGE_SIZE;
			}
				
retrygetspace:
			if (!swap_pager_full && ntoget > 1 &&
				swap_pager_getswapspace(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(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;
			} 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;
		}
	}

	for(i = 0; i < count; i++) {
		if( rtvals[i] != VM_PAGER_OK) {
			if( swb[i])
				--swb[i]->swb_locked;
		}
	}

	for(i = 0; i < count; i++)
		if( rtvals[i] != VM_PAGER_OK)
			break;

	if( i == 0) {
		return VM_PAGER_AGAIN;
	}

	count = i;
	for(i=0;i<count;i++) {
		if( reqaddr[i] == SWB_EMPTY)
			printf("I/O to empty block????\n");
	}
				
	/*
	 */
	
	/*
	 * For synchronous writes, we clean up
	 * all completed async pageouts.
	 */
	if ((flags & B_ASYNC) == 0) {
		swap_pager_clean();
	}

	kva = 0;

	/*
	 * we allocate a new kva for transfers > 1 page
	 * but for transfers == 1 page, the swap_pager_free list contains
	 * entries that have pre-allocated kva's (for efficiency).
	 */
	if ( count > 1) {
		kva = kmem_alloc_pageable(pager_map, count*PAGE_SIZE);
		if( !kva) {
			for (i = 0; i < count; i++) {
				if( swb[i])
					--swb[i]->swb_locked;
				rtvals[i] = VM_PAGER_AGAIN;
			}
			return VM_PAGER_AGAIN;
		}
	} 

	/*
	 * get a swap pager clean data structure, block until we get it
	 */
	if (swap_pager_free.tqh_first == NULL) {
/*
		if (flags & B_ASYNC) {
			for(i=0;i<count;i++) {
				rtvals[i] = VM_PAGER_AGAIN;
				if( swb[i])
					--swb[i]->swb_locked;
			}
			return VM_PAGER_AGAIN;
		}
*/

		s = splbio();
		if( curproc == pageproc)
			(void) swap_pager_clean();
		else
			wakeup((caddr_t) &vm_pages_needed);
		while (swap_pager_free.tqh_first == NULL) { 
			swap_pager_needflags |= SWAP_FREE_NEEDED;
			tsleep((caddr_t)&swap_pager_free,
				PVM, "swpfre", 0);
			if( curproc == pageproc)
				(void) swap_pager_clean();
			else
				wakeup((caddr_t) &vm_pages_needed);
		}
		splx(s);
	}

	spc = swap_pager_free.tqh_first;
	TAILQ_REMOVE(&swap_pager_free, spc, spc_list);
	if( !kva) {
		kva = spc->spc_kva;
		spc->spc_altkva = 0;
	} else {
		spc->spc_altkva = kva;
	}

	/*
	 * map our page(s) into kva for I/O
	 */
	for (i = 0; i < count; i++) {
		pmap_kenter( kva + PAGE_SIZE * i, VM_PAGE_TO_PHYS(m[i]));
	}
	pmap_update();

	/*
	 * get the base I/O offset into the swap file
	 */
	for(i=0;i<count;i++) {
		foff = m[i]->offset + paging_offset;
		off = swap_pager_block_offset(swp, foff);
		/*
		 * if we are setting the valid bit anew,
		 * then diminish the swap free space
		 */
		if( (swb[i]->swb_valid & (1 << off)) == 0)
			vm_swap_size -= btodb(PAGE_SIZE);
			
		/*
		 * set the valid bit
		 */
		swb[i]->swb_valid |= (1 << off);
		/*
		 * and unlock the data structure
		 */
		--swb[i]->swb_locked;
	}

	s = splbio();
	/*
	 * Get a swap buffer header and perform the IO
	 */
	bp = spc->spc_bp;
	bzero(bp, sizeof *bp);
	bp->b_spc = spc;

	bp->b_flags = B_BUSY;
	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_un.b_addr = (caddr_t) kva;
	bp->b_blkno = reqaddr[0];
	bgetvp( swapdev_vp, bp);
/*
	VHOLD(swapdev_vp);
	bp->b_vp = swapdev_vp;
	if (swapdev_vp->v_type == VBLK)
		bp->b_dev = swapdev_vp->v_rdev;
*/
	bp->b_bcount = PAGE_SIZE*count;
	bp->b_bufsize = PAGE_SIZE*count;
	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.
	 */
	if ( flags & B_ASYNC ) {
		spc->spc_flags = 0;
		spc->spc_swp = swp;
		for(i=0;i<count;i++)
			spc->spc_m[i] = m[i];
		spc->spc_count = count;
		/*
		 * 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;
		swp->sw_poip++;
		TAILQ_INSERT_TAIL(&swap_pager_inuse, spc, spc_list);
	} else {
		swp->sw_poip++;
		bp->b_flags |= B_CALL;
		bp->b_iodone = swap_pager_iodone1;
	}
	/*
	 * perform the I/O
	 */
	VOP_STRATEGY(bp);
	if ((flags & (B_READ|B_ASYNC)) == B_ASYNC ) {
		if ((bp->b_flags & B_DONE) == B_DONE) {
			swap_pager_clean();
		}
		splx(s);
		for(i=0;i<count;i++) {
			rtvals[i] = VM_PAGER_PEND;
		}
		return VM_PAGER_PEND;
	}

	/*
	 * wait for the sync I/O to complete
	 */
	while ((bp->b_flags & B_DONE) == 0) {
		tsleep((caddr_t)bp, PVM, "swwrt", 0);
	}
	rv = (bp->b_flags & B_ERROR) ? VM_PAGER_FAIL : VM_PAGER_OK;
	bp->b_flags &= ~(B_BUSY|B_WANTED|B_PHYS|B_DIRTY|B_CALL|B_DONE);

	--swp->sw_poip;
	if (swp->sw_poip == 0)
		wakeup((caddr_t) swp);
		
	if (bp->b_vp)
		brelvp(bp);

	splx(s);

	/*
	 * remove the mapping for kernel virtual
	 */
	pmap_remove(vm_map_pmap(pager_map), kva, kva + count * PAGE_SIZE);

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

	if( spc->spc_altkva)
		kmem_free_wakeup(pager_map, kva, count * PAGE_SIZE);

	if( bp->b_rcred != NOCRED)
		crfree(bp->b_rcred);
	if( bp->b_wcred != NOCRED)
		crfree(bp->b_wcred);
	TAILQ_INSERT_TAIL(&swap_pager_free, spc, spc_list);
	if (swap_pager_needflags & SWAP_FREE_NEEDED) {
		swap_pager_needflags &= ~SWAP_FREE_NEEDED;
		wakeup((caddr_t)&swap_pager_free);
	}

	return(rv);
}

boolean_t
swap_pager_clean()
{
	register swp_clean_t spc, tspc;
	register int s;

	tspc = NULL;
	if (swap_pager_done.tqh_first == NULL)
		return FALSE;
	for (;;) {
		s = splbio();
		/*
		 * Look up and removal from done list must be done
		 * at splbio() to avoid conflicts with swap_pager_iodone.
		 */
		while (spc = swap_pager_done.tqh_first) {
			if( spc->spc_altkva) {
				pmap_remove(vm_map_pmap(pager_map), spc->spc_altkva, spc->spc_altkva + spc->spc_count * PAGE_SIZE);
				kmem_free_wakeup(pager_map, spc->spc_altkva, spc->spc_count * PAGE_SIZE);
				spc->spc_altkva = 0;
			} else {
				pmap_remove(vm_map_pmap(pager_map), spc->spc_kva, spc->spc_kva + PAGE_SIZE);
			}
			swap_pager_finish(spc);
			TAILQ_REMOVE(&swap_pager_done, spc, spc_list);
			goto doclean;
		}

		/*
		 * No operations done, thats all we can do for now.
		 */

		splx(s);
		break;

		/*
		 * The desired page was found to be busy earlier in
		 * the scan but has since completed.
		 */
doclean:
		if (tspc && tspc == spc) {
			tspc = NULL;
		}
		spc->spc_flags = 0;
		TAILQ_INSERT_TAIL(&swap_pager_free, spc, spc_list);
		if (swap_pager_needflags & SWAP_FREE_NEEDED) {
			swap_pager_needflags &= ~SWAP_FREE_NEEDED;
			wakeup((caddr_t)&swap_pager_free);
		}
		++cleandone;
		splx(s);
	}

	return(tspc ? TRUE : FALSE);
}

void
swap_pager_finish(spc)
	register swp_clean_t spc;
{
	vm_object_t object = spc->spc_m[0]->object;
	int i;

	if ((object->paging_in_progress -= spc->spc_count) == 0) 
		thread_wakeup((int) object);

	/*
	 * 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=0;i<spc->spc_count;i++) {
			printf("swap_pager_finish: clean of page %x failed\n",
			       VM_PAGE_TO_PHYS(spc->spc_m[i]));
			spc->spc_m[i]->flags |= PG_LAUNDRY;
		}
	} else {
		for(i=0;i<spc->spc_count;i++) {
			pmap_clear_modify(VM_PAGE_TO_PHYS(spc->spc_m[i]));
			spc->spc_m[i]->flags |= PG_CLEAN;
		}
	}


	for(i=0;i<spc->spc_count;i++) {
		/*
		 * we wakeup any processes that are waiting on
		 * these pages.
		 */
		PAGE_WAKEUP(spc->spc_m[i]);
	}
	nswiodone -= spc->spc_count;

	return;
}

/*
 * swap_pager_iodone
 */
void
swap_pager_iodone(bp)
	register struct buf *bp;
{
	register swp_clean_t spc;
	int s;

	s = splbio();
	spc = (swp_clean_t) bp->b_spc;
	TAILQ_REMOVE(&swap_pager_inuse, spc, spc_list);
	TAILQ_INSERT_TAIL(&swap_pager_done, spc, spc_list);
	if (bp->b_flags & B_ERROR) {
		spc->spc_flags |= SPC_ERROR;
		printf("error %d blkno %d sz %d ",
			bp->b_error, bp->b_blkno, bp->b_bcount);
	}

/*
	if ((bp->b_flags & B_READ) == 0)
		vwakeup(bp);
*/
		
	bp->b_flags &= ~(B_BUSY|B_WANTED|B_PHYS|B_DIRTY|B_ASYNC);
	if (bp->b_vp) {
		brelvp(bp);
	}
	if( bp->b_rcred != NOCRED)
		crfree(bp->b_rcred);
	if( bp->b_wcred != NOCRED)
		crfree(bp->b_wcred);

	nswiodone += spc->spc_count;
	if (--spc->spc_swp->sw_poip == 0) {
		wakeup((caddr_t)spc->spc_swp);
	}

	if ((swap_pager_needflags & SWAP_FREE_NEEDED) ||
	    swap_pager_inuse.tqh_first == 0) { 
		swap_pager_needflags &= ~SWAP_FREE_NEEDED;
		wakeup((caddr_t)&swap_pager_free);
		wakeup((caddr_t)&vm_pages_needed);
	}

	if (vm_pageout_pages_needed) {
		wakeup((caddr_t)&vm_pageout_pages_needed);
	}

	if ((swap_pager_inuse.tqh_first == NULL) ||
	    (cnt.v_free_count < cnt.v_free_min &&
	    nswiodone + cnt.v_free_count >= cnt.v_free_min) ) {
		wakeup((caddr_t)&vm_pages_needed);
	}
	splx(s);
}

int bswneeded;
/* TAILQ_HEAD(swqueue, buf) bswlist; */
/*
 * allocate a physical buffer 
 */
struct buf *
getpbuf() {
	int s;
	struct buf *bp;

	s = splbio();
	/* get a bp from the swap buffer header pool */
	while ((bp = bswlist.tqh_first) == NULL) {
		bswneeded = 1;
		tsleep((caddr_t)&bswneeded, PVM, "wswbuf", 0); 
	}
	TAILQ_REMOVE(&bswlist, bp, b_freelist);

	splx(s);

	bzero(bp, sizeof *bp);
	bp->b_rcred = NOCRED;
	bp->b_wcred = NOCRED;
	return bp;
}

/*
 * allocate a physical buffer, if one is available
 */
struct buf *
trypbuf() {
	int s;
	struct buf *bp;

	s = splbio();
	if ((bp = bswlist.tqh_first) == NULL) {
		splx(s);
		return NULL;
	}
	TAILQ_REMOVE(&bswlist, bp, b_freelist);
	splx(s);

	bzero(bp, sizeof *bp);
	bp->b_rcred = NOCRED;
	bp->b_wcred = NOCRED;
	return bp;
}

/*
 * release a physical buffer
 */
void
relpbuf(bp)
	struct buf *bp;
{
	int s;

	s = splbio();

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

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

	TAILQ_INSERT_HEAD(&bswlist, bp, b_freelist);

	if (bswneeded) {
		bswneeded = 0;
		wakeup((caddr_t)&bswlist);
	}
	splx(s);
}

/*
 * return true if any swap control structures can be allocated
 */
int
swap_pager_ready() {
	if( swap_pager_free.tqh_first)
		return 1;
	else
		return 0;
}