2 * Copyright (c) 1998 Matthew Dillon,
3 * Copyright (c) 1994 John S. Dyson
4 * Copyright (c) 1990 University of Utah.
5 * Copyright (c) 1991, 1993
6 * The Regents of the University of California. All rights reserved.
8 * This code is derived from software contributed to Berkeley by
9 * the Systems Programming Group of the University of Utah Computer
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. All advertising materials mentioning features or use of this software
21 * must display the following acknowledgement:
22 * This product includes software developed by the University of
23 * California, Berkeley and its contributors.
24 * 4. Neither the name of the University nor the names of its contributors
25 * may be used to endorse or promote products derived from this software
26 * without specific prior written permission.
28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
43 * Radix Bitmap 'blists'.
45 * - The new swapper uses the new radix bitmap code. This should scale
46 * to arbitrarily small or arbitrarily large swap spaces and an almost
47 * arbitrary degree of fragmentation.
51 * - on the fly reallocation of swap during putpages. The new system
52 * does not try to keep previously allocated swap blocks for dirty
55 * - on the fly deallocation of swap
57 * - No more garbage collection required. Unnecessarily allocated swap
58 * blocks only exist for dirty vm_page_t's now and these are already
59 * cycled (in a high-load system) by the pager. We also do on-the-fly
60 * removal of invalidated swap blocks when a page is destroyed
63 * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
65 * @(#)swap_pager.c 8.9 (Berkeley) 3/21/94
67 * $FreeBSD: src/sys/vm/swap_pager.c,v 1.130.2.12 2002/08/31 21:15:55 dillon Exp $
68 * $DragonFly: src/sys/vm/swap_pager.c,v 1.11 2004/03/23 22:54:32 dillon Exp $
71 #include <sys/param.h>
72 #include <sys/systm.h>
74 #include <sys/kernel.h>
77 #include <sys/vnode.h>
78 #include <sys/malloc.h>
79 #include <sys/vmmeter.h>
80 #include <sys/sysctl.h>
81 #include <sys/blist.h>
83 #include <sys/vmmeter.h>
85 #ifndef MAX_PAGEOUT_CLUSTER
86 #define MAX_PAGEOUT_CLUSTER 16
89 #define SWB_NPAGES MAX_PAGEOUT_CLUSTER
93 #include <vm/vm_object.h>
94 #include <vm/vm_page.h>
95 #include <vm/vm_pager.h>
96 #include <vm/vm_pageout.h>
97 #include <vm/swap_pager.h>
98 #include <vm/vm_extern.h>
99 #include <vm/vm_zone.h>
101 #include <sys/buf2.h>
102 #include <vm/vm_page2.h>
104 #define SWM_FREE 0x02 /* free, period */
105 #define SWM_POP 0x04 /* pop out */
108 * vm_swap_size is in page-sized chunks now. It was DEV_BSIZE'd chunks
112 extern int vm_swap_size; /* number of free swap blocks, in pages */
114 int swap_pager_full; /* swap space exhaustion (task killing) */
115 static int swap_pager_almost_full; /* swap space exhaustion (w/ hysteresis)*/
116 static int nsw_rcount; /* free read buffers */
117 static int nsw_wcount_sync; /* limit write buffers / synchronous */
118 static int nsw_wcount_async; /* limit write buffers / asynchronous */
119 static int nsw_wcount_async_max;/* assigned maximum */
120 static int nsw_cluster_max; /* maximum VOP I/O allowed */
121 static int sw_alloc_interlock; /* swap pager allocation interlock */
123 struct blist *swapblist;
124 static struct swblock **swhash;
125 static int swhash_mask;
126 static int swap_async_max = 4; /* maximum in-progress async I/O's */
128 extern struct vnode *swapdev_vp; /* from vm_swap.c */
130 SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
131 CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");
134 * "named" and "unnamed" anon region objects. Try to reduce the overhead
135 * of searching a named list by hashing it just a little.
140 #define NOBJLIST(handle) \
141 (&swap_pager_object_list[((int)(intptr_t)handle >> 4) & (NOBJLISTS-1)])
143 static struct pagerlst swap_pager_object_list[NOBJLISTS];
144 struct pagerlst swap_pager_un_object_list;
148 * pagerops for OBJT_SWAP - "swap pager". Some ops are also global procedure
149 * calls hooked from other parts of the VM system and do not appear here.
150 * (see vm/swap_pager.h).
154 swap_pager_alloc (void *handle, vm_ooffset_t size,
155 vm_prot_t prot, vm_ooffset_t offset);
156 static void swap_pager_dealloc (vm_object_t object);
157 static int swap_pager_getpages (vm_object_t, vm_page_t *, int, int);
158 static void swap_pager_init (void);
159 static void swap_pager_unswapped (vm_page_t);
160 static void swap_pager_strategy (vm_object_t, struct buf *);
162 struct pagerops swappagerops = {
163 swap_pager_init, /* early system initialization of pager */
164 swap_pager_alloc, /* allocate an OBJT_SWAP object */
165 swap_pager_dealloc, /* deallocate an OBJT_SWAP object */
166 swap_pager_getpages, /* pagein */
167 swap_pager_putpages, /* pageout */
168 swap_pager_haspage, /* get backing store status for page */
169 swap_pager_unswapped, /* remove swap related to page */
170 swap_pager_strategy /* pager strategy call */
174 * dmmax is in page-sized chunks with the new swap system. It was
175 * dev-bsized chunks in the old. dmmax is always a power of 2.
177 * swap_*() routines are externally accessible. swp_*() routines are
182 static int dmmax_mask;
183 int nswap_lowat = 128; /* in pages, swap_pager_almost_full warn */
184 int nswap_hiwat = 512; /* in pages, swap_pager_almost_full warn */
186 static __inline void swp_sizecheck (void);
187 static void swp_pager_sync_iodone (struct buf *bp);
188 static void swp_pager_async_iodone (struct buf *bp);
191 * Swap bitmap functions
194 static __inline void swp_pager_freeswapspace (daddr_t blk, int npages);
195 static __inline daddr_t swp_pager_getswapspace (int npages);
201 static void swp_pager_meta_build (vm_object_t, vm_pindex_t, daddr_t);
202 static void swp_pager_meta_free (vm_object_t, vm_pindex_t, daddr_t);
203 static void swp_pager_meta_free_all (vm_object_t);
204 static daddr_t swp_pager_meta_ctl (vm_object_t, vm_pindex_t, int);
207 * SWP_SIZECHECK() - update swap_pager_full indication
209 * update the swap_pager_almost_full indication and warn when we are
210 * about to run out of swap space, using lowat/hiwat hysteresis.
212 * Clear swap_pager_full ( task killing ) indication when lowat is met.
214 * No restrictions on call
215 * This routine may not block.
216 * This routine must be called at splvm()
222 if (vm_swap_size < nswap_lowat) {
223 if (swap_pager_almost_full == 0) {
224 printf("swap_pager: out of swap space\n");
225 swap_pager_almost_full = 1;
229 if (vm_swap_size > nswap_hiwat)
230 swap_pager_almost_full = 0;
235 * SWAP_PAGER_INIT() - initialize the swap pager!
237 * Expected to be started from system init. NOTE: This code is run
238 * before much else so be careful what you depend on. Most of the VM
239 * system has yet to be initialized at this point.
243 swap_pager_init(void)
246 * Initialize object lists
250 for (i = 0; i < NOBJLISTS; ++i)
251 TAILQ_INIT(&swap_pager_object_list[i]);
252 TAILQ_INIT(&swap_pager_un_object_list);
255 * Device Stripe, in PAGE_SIZE'd blocks
258 dmmax = SWB_NPAGES * 2;
259 dmmax_mask = ~(dmmax - 1);
263 * SWAP_PAGER_SWAP_INIT() - swap pager initialization from pageout process
265 * Expected to be started from pageout process once, prior to entering
270 swap_pager_swap_init(void)
275 * Number of in-transit swap bp operations. Don't
276 * exhaust the pbufs completely. Make sure we
277 * initialize workable values (0 will work for hysteresis
278 * but it isn't very efficient).
280 * The nsw_cluster_max is constrained by the bp->b_pages[]
281 * array (MAXPHYS/PAGE_SIZE) and our locally defined
282 * MAX_PAGEOUT_CLUSTER. Also be aware that swap ops are
283 * constrained by the swap device interleave stripe size.
285 * Currently we hardwire nsw_wcount_async to 4. This limit is
286 * designed to prevent other I/O from having high latencies due to
287 * our pageout I/O. The value 4 works well for one or two active swap
288 * devices but is probably a little low if you have more. Even so,
289 * a higher value would probably generate only a limited improvement
290 * with three or four active swap devices since the system does not
291 * typically have to pageout at extreme bandwidths. We will want
292 * at least 2 per swap devices, and 4 is a pretty good value if you
293 * have one NFS swap device due to the command/ack latency over NFS.
294 * So it all works out pretty well.
297 nsw_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
299 nsw_rcount = (nswbuf + 1) / 2;
300 nsw_wcount_sync = (nswbuf + 3) / 4;
301 nsw_wcount_async = 4;
302 nsw_wcount_async_max = nsw_wcount_async;
305 * Initialize our zone. Right now I'm just guessing on the number
306 * we need based on the number of pages in the system. Each swblock
307 * can hold 16 pages, so this is probably overkill. This reservation
308 * is typically limited to around 32MB by default.
310 n = vmstats.v_page_count / 2;
311 if (maxswzone && n > maxswzone / sizeof(struct swblock))
312 n = maxswzone / sizeof(struct swblock);
318 sizeof(struct swblock),
322 if (swap_zone != NULL)
325 * if the allocation failed, try a zone two thirds the
326 * size of the previous attempt.
331 if (swap_zone == NULL)
332 panic("swap_pager_swap_init: swap_zone == NULL");
334 printf("Swap zone entries reduced from %d to %d.\n", n2, n);
338 * Initialize our meta-data hash table. The swapper does not need to
339 * be quite as efficient as the VM system, so we do not use an
340 * oversized hash table.
342 * n: size of hash table, must be power of 2
343 * swhash_mask: hash table index mask
346 for (n = 1; n < n2 / 8; n *= 2)
349 swhash = malloc(sizeof(struct swblock *) * n, M_VMPGDATA, M_WAITOK);
350 bzero(swhash, sizeof(struct swblock *) * n);
356 * SWAP_PAGER_ALLOC() - allocate a new OBJT_SWAP VM object and instantiate
357 * its metadata structures.
359 * This routine is called from the mmap and fork code to create a new
360 * OBJT_SWAP object. We do this by creating an OBJT_DEFAULT object
361 * and then converting it with swp_pager_meta_build().
363 * This routine may block in vm_object_allocate() and create a named
364 * object lookup race, so we must interlock. We must also run at
365 * splvm() for the object lookup to handle races with interrupts, but
366 * we do not have to maintain splvm() in between the lookup and the
367 * add because (I believe) it is not possible to attempt to create
368 * a new swap object w/handle when a default object with that handle
373 swap_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
380 * Reference existing named region or allocate new one. There
381 * should not be a race here against swp_pager_meta_build()
382 * as called from vm_page_remove() in regards to the lookup
386 while (sw_alloc_interlock) {
387 sw_alloc_interlock = -1;
388 tsleep(&sw_alloc_interlock, 0, "swpalc", 0);
390 sw_alloc_interlock = 1;
392 object = vm_pager_object_lookup(NOBJLIST(handle), handle);
394 if (object != NULL) {
395 vm_object_reference(object);
397 object = vm_object_allocate(OBJT_DEFAULT,
398 OFF_TO_IDX(offset + PAGE_MASK + size));
399 object->handle = handle;
401 swp_pager_meta_build(object, 0, SWAPBLK_NONE);
404 if (sw_alloc_interlock < 0)
405 wakeup(&sw_alloc_interlock);
407 sw_alloc_interlock = 0;
409 object = vm_object_allocate(OBJT_DEFAULT,
410 OFF_TO_IDX(offset + PAGE_MASK + size));
412 swp_pager_meta_build(object, 0, SWAPBLK_NONE);
419 * SWAP_PAGER_DEALLOC() - remove swap metadata from object
421 * The swap backing for the object is destroyed. The code is
422 * designed such that we can reinstantiate it later, but this
423 * routine is typically called only when the entire object is
424 * about to be destroyed.
426 * This routine may block, but no longer does.
428 * The object must be locked or unreferenceable.
432 swap_pager_dealloc(vm_object_t object)
437 * Remove from list right away so lookups will fail if we block for
438 * pageout completion.
441 if (object->handle == NULL) {
442 TAILQ_REMOVE(&swap_pager_un_object_list, object, pager_object_list);
444 TAILQ_REMOVE(NOBJLIST(object->handle), object, pager_object_list);
447 vm_object_pip_wait(object, "swpdea");
450 * Free all remaining metadata. We only bother to free it from
451 * the swap meta data. We do not attempt to free swapblk's still
452 * associated with vm_page_t's for this object. We do not care
453 * if paging is still in progress on some objects.
456 swp_pager_meta_free_all(object);
460 /************************************************************************
461 * SWAP PAGER BITMAP ROUTINES *
462 ************************************************************************/
465 * SWP_PAGER_GETSWAPSPACE() - allocate raw swap space
467 * Allocate swap for the requested number of pages. The starting
468 * swap block number (a page index) is returned or SWAPBLK_NONE
469 * if the allocation failed.
471 * Also has the side effect of advising that somebody made a mistake
472 * when they configured swap and didn't configure enough.
474 * Must be called at splvm() to avoid races with bitmap frees from
475 * vm_page_remove() aka swap_pager_page_removed().
477 * This routine may not block
478 * This routine must be called at splvm().
481 static __inline daddr_t
482 swp_pager_getswapspace(int npages)
486 if ((blk = blist_alloc(swapblist, npages)) == SWAPBLK_NONE) {
487 if (swap_pager_full != 2) {
488 printf("swap_pager_getswapspace: failed\n");
490 swap_pager_almost_full = 1;
493 vm_swap_size -= npages;
500 * SWP_PAGER_FREESWAPSPACE() - free raw swap space
502 * This routine returns the specified swap blocks back to the bitmap.
504 * Note: This routine may not block (it could in the old swap code),
505 * and through the use of the new blist routines it does not block.
507 * We must be called at splvm() to avoid races with bitmap frees from
508 * vm_page_remove() aka swap_pager_page_removed().
510 * This routine may not block
511 * This routine must be called at splvm().
515 swp_pager_freeswapspace(daddr_t blk, int npages)
517 blist_free(swapblist, blk, npages);
518 vm_swap_size += npages;
523 * SWAP_PAGER_FREESPACE() - frees swap blocks associated with a page
524 * range within an object.
526 * This is a globally accessible routine.
528 * This routine removes swapblk assignments from swap metadata.
530 * The external callers of this routine typically have already destroyed
531 * or renamed vm_page_t's associated with this range in the object so
534 * This routine may be called at any spl. We up our spl to splvm temporarily
535 * in order to perform the metadata removal.
539 swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_size_t size)
542 swp_pager_meta_free(object, start, size);
547 * SWAP_PAGER_RESERVE() - reserve swap blocks in object
549 * Assigns swap blocks to the specified range within the object. The
550 * swap blocks are not zerod. Any previous swap assignment is destroyed.
552 * Returns 0 on success, -1 on failure.
556 swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
560 daddr_t blk = SWAPBLK_NONE;
561 vm_pindex_t beg = start; /* save start index */
567 while ((blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE) {
570 swp_pager_meta_free(object, beg, start - beg);
576 swp_pager_meta_build(object, start, blk);
582 swp_pager_meta_free(object, start, n);
588 * SWAP_PAGER_COPY() - copy blocks from source pager to destination pager
589 * and destroy the source.
591 * Copy any valid swapblks from the source to the destination. In
592 * cases where both the source and destination have a valid swapblk,
593 * we keep the destination's.
595 * This routine is allowed to block. It may block allocating metadata
596 * indirectly through swp_pager_meta_build() or if paging is still in
597 * progress on the source.
599 * This routine can be called at any spl
601 * XXX vm_page_collapse() kinda expects us not to block because we
602 * supposedly do not need to allocate memory, but for the moment we
603 * *may* have to get a little memory from the zone allocator, but
604 * it is taken from the interrupt memory. We should be ok.
606 * The source object contains no vm_page_t's (which is just as well)
608 * The source object is of type OBJT_SWAP.
610 * The source and destination objects must be locked or
611 * inaccessible (XXX are they ?)
615 swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
616 vm_pindex_t offset, int destroysource)
624 * If destroysource is set, we remove the source object from the
625 * swap_pager internal queue now.
629 if (srcobject->handle == NULL) {
631 &swap_pager_un_object_list,
637 NOBJLIST(srcobject->handle),
645 * transfer source to destination.
648 for (i = 0; i < dstobject->size; ++i) {
652 * Locate (without changing) the swapblk on the destination,
653 * unless it is invalid in which case free it silently, or
654 * if the destination is a resident page, in which case the
655 * source is thrown away.
658 dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
660 if (dstaddr == SWAPBLK_NONE) {
662 * Destination has no swapblk and is not resident,
667 srcaddr = swp_pager_meta_ctl(
673 if (srcaddr != SWAPBLK_NONE)
674 swp_pager_meta_build(dstobject, i, srcaddr);
677 * Destination has valid swapblk or it is represented
678 * by a resident page. We destroy the sourceblock.
681 swp_pager_meta_ctl(srcobject, i + offset, SWM_FREE);
686 * Free left over swap blocks in source.
688 * We have to revert the type to OBJT_DEFAULT so we do not accidently
689 * double-remove the object from the swap queues.
693 swp_pager_meta_free_all(srcobject);
695 * Reverting the type is not necessary, the caller is going
696 * to destroy srcobject directly, but I'm doing it here
697 * for consistency since we've removed the object from its
700 srcobject->type = OBJT_DEFAULT;
706 * SWAP_PAGER_HASPAGE() - determine if we have good backing store for
707 * the requested page.
709 * We determine whether good backing store exists for the requested
710 * page and return TRUE if it does, FALSE if it doesn't.
712 * If TRUE, we also try to determine how much valid, contiguous backing
713 * store exists before and after the requested page within a reasonable
714 * distance. We do not try to restrict it to the swap device stripe
715 * (that is handled in getpages/putpages). It probably isn't worth
720 swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
727 * do we have good backing store at the requested index ?
731 blk0 = swp_pager_meta_ctl(object, pindex, 0);
733 if (blk0 == SWAPBLK_NONE) {
743 * find backwards-looking contiguous good backing store
746 if (before != NULL) {
749 for (i = 1; i < (SWB_NPAGES/2); ++i) {
754 blk = swp_pager_meta_ctl(object, pindex - i, 0);
762 * find forward-looking contiguous good backing store
768 for (i = 1; i < (SWB_NPAGES/2); ++i) {
771 blk = swp_pager_meta_ctl(object, pindex + i, 0);
782 * SWAP_PAGER_PAGE_UNSWAPPED() - remove swap backing store related to page
784 * This removes any associated swap backing store, whether valid or
785 * not, from the page.
787 * This routine is typically called when a page is made dirty, at
788 * which point any associated swap can be freed. MADV_FREE also
789 * calls us in a special-case situation
791 * NOTE!!! If the page is clean and the swap was valid, the caller
792 * should make the page dirty before calling this routine. This routine
793 * does NOT change the m->dirty status of the page. Also: MADV_FREE
796 * This routine may not block
797 * This routine must be called at splvm()
801 swap_pager_unswapped(vm_page_t m)
803 swp_pager_meta_ctl(m->object, m->pindex, SWM_FREE);
807 * SWAP_PAGER_STRATEGY() - read, write, free blocks
809 * This implements the vm_pager_strategy() interface to swap and allows
810 * other parts of the system to directly access swap as backing store
811 * through vm_objects of type OBJT_SWAP. This is intended to be a
812 * cacheless interface ( i.e. caching occurs at higher levels ).
813 * Therefore we do not maintain any resident pages. All I/O goes
814 * directly to and from the swap device.
816 * Note that b_blkno is scaled for PAGE_SIZE
818 * We currently attempt to run I/O synchronously or asynchronously as
819 * the caller requests. This isn't perfect because we loose error
820 * sequencing when we run multiple ops in parallel to satisfy a request.
821 * But this is swap, so we let it all hang out.
825 swap_pager_strategy(vm_object_t object, struct buf *bp)
831 struct buf *nbp = NULL;
833 if (bp->b_bcount & PAGE_MASK) {
834 bp->b_error = EINVAL;
835 bp->b_flags |= B_ERROR | B_INVAL;
837 printf("swap_pager_strategy: bp %p b_vp %p blk %d size %d, not page bounded\n", bp, bp->b_vp, (int)bp->b_pblkno, (int)bp->b_bcount);
842 * Clear error indication, initialize page index, count, data pointer.
846 bp->b_flags &= ~B_ERROR;
847 bp->b_resid = bp->b_bcount;
849 start = bp->b_pblkno;
850 count = howmany(bp->b_bcount, PAGE_SIZE);
856 * Deal with B_FREEBUF
859 if (bp->b_flags & B_FREEBUF) {
861 * FREE PAGE(s) - destroy underlying swap that is no longer
864 swp_pager_meta_free(object, start, count);
872 * Execute read or write
879 * Obtain block. If block not found and writing, allocate a
880 * new block and build it into the object.
883 blk = swp_pager_meta_ctl(object, start, 0);
884 if ((blk == SWAPBLK_NONE) && (bp->b_flags & B_READ) == 0) {
885 blk = swp_pager_getswapspace(1);
886 if (blk == SWAPBLK_NONE) {
887 bp->b_error = ENOMEM;
888 bp->b_flags |= B_ERROR;
891 swp_pager_meta_build(object, start, blk);
895 * Do we have to flush our current collection? Yes if:
897 * - no swap block at this index
898 * - swap block is not contiguous
899 * - we cross a physical disk boundry in the
904 nbp && (nbp->b_blkno + btoc(nbp->b_bcount) != blk ||
905 ((nbp->b_blkno ^ blk) & dmmax_mask)
909 if (bp->b_flags & B_READ) {
910 ++mycpu->gd_cnt.v_swapin;
911 mycpu->gd_cnt.v_swappgsin += btoc(nbp->b_bcount);
913 ++mycpu->gd_cnt.v_swapout;
914 mycpu->gd_cnt.v_swappgsout += btoc(nbp->b_bcount);
915 nbp->b_dirtyend = nbp->b_bcount;
923 * Add new swapblk to nbp, instantiating nbp if necessary.
924 * Zero-fill reads are able to take a shortcut.
927 if (blk == SWAPBLK_NONE) {
929 * We can only get here if we are reading. Since
930 * we are at splvm() we can safely modify b_resid,
931 * even if chain ops are in progress.
933 bzero(data, PAGE_SIZE);
934 bp->b_resid -= PAGE_SIZE;
937 nbp = getchainbuf(bp, swapdev_vp, (bp->b_flags & B_READ) | B_ASYNC);
942 nbp->b_bcount += PAGE_SIZE;
950 * Flush out last buffer
956 if ((bp->b_flags & B_ASYNC) == 0)
957 nbp->b_flags &= ~B_ASYNC;
958 if (nbp->b_flags & B_READ) {
959 ++mycpu->gd_cnt.v_swapin;
960 mycpu->gd_cnt.v_swappgsin += btoc(nbp->b_bcount);
962 ++mycpu->gd_cnt.v_swapout;
963 mycpu->gd_cnt.v_swappgsout += btoc(nbp->b_bcount);
964 nbp->b_dirtyend = nbp->b_bcount;
971 * Wait for completion.
974 if (bp->b_flags & B_ASYNC) {
977 waitchainbuf(bp, 0, 1);
982 * SWAP_PAGER_GETPAGES() - bring pages in from swap
984 * Attempt to retrieve (m, count) pages from backing store, but make
985 * sure we retrieve at least m[reqpage]. We try to load in as large
986 * a chunk surrounding m[reqpage] as is contiguous in swap and which
987 * belongs to the same object.
989 * The code is designed for asynchronous operation and
990 * immediate-notification of 'reqpage' but tends not to be
991 * used that way. Please do not optimize-out this algorithmic
992 * feature, I intend to improve on it in the future.
994 * The parent has a single vm_object_pip_add() reference prior to
995 * calling us and we should return with the same.
997 * The parent has BUSY'd the pages. We should return with 'm'
998 * left busy, but the others adjusted.
1002 swap_pager_getpages(vm_object_t object, vm_page_t *m, int count, int reqpage)
1011 vm_pindex_t lastpindex;
1015 if (mreq->object != object) {
1016 panic("swap_pager_getpages: object mismatch %p/%p",
1022 * Calculate range to retrieve. The pages have already been assigned
1023 * their swapblks. We require a *contiguous* range that falls entirely
1024 * within a single device stripe. If we do not supply it, bad things
1025 * happen. Note that blk, iblk & jblk can be SWAPBLK_NONE, but the
1026 * loops are set up such that the case(s) are handled implicitly.
1028 * The swp_*() calls must be made at splvm(). vm_page_free() does
1029 * not need to be, but it will go a little faster if it is.
1033 blk = swp_pager_meta_ctl(mreq->object, mreq->pindex, 0);
1035 for (i = reqpage - 1; i >= 0; --i) {
1038 iblk = swp_pager_meta_ctl(m[i]->object, m[i]->pindex, 0);
1039 if (blk != iblk + (reqpage - i))
1041 if ((blk ^ iblk) & dmmax_mask)
1046 for (j = reqpage + 1; j < count; ++j) {
1049 jblk = swp_pager_meta_ctl(m[j]->object, m[j]->pindex, 0);
1050 if (blk != jblk - (j - reqpage))
1052 if ((blk ^ jblk) & dmmax_mask)
1057 * free pages outside our collection range. Note: we never free
1058 * mreq, it must remain busy throughout.
1064 for (k = 0; k < i; ++k)
1066 for (k = j; k < count; ++k)
1073 * Return VM_PAGER_FAIL if we have nothing to do. Return mreq
1074 * still busy, but the others unbusied.
1077 if (blk == SWAPBLK_NONE)
1078 return(VM_PAGER_FAIL);
1081 * Get a swap buffer header to perform the IO
1084 bp = getpbuf(&nsw_rcount);
1085 kva = (vm_offset_t) bp->b_data;
1088 * map our page(s) into kva for input
1090 * NOTE: B_PAGING is set by pbgetvp()
1093 pmap_qenter(kva, m + i, j - i);
1095 bp->b_flags = B_READ | B_CALL;
1096 bp->b_iodone = swp_pager_async_iodone;
1097 bp->b_data = (caddr_t) kva;
1098 bp->b_blkno = blk - (reqpage - i);
1099 bp->b_bcount = PAGE_SIZE * (j - i);
1100 bp->b_bufsize = PAGE_SIZE * (j - i);
1101 bp->b_pager.pg_reqpage = reqpage - i;
1106 for (k = i; k < j; ++k) {
1107 bp->b_pages[k - i] = m[k];
1108 vm_page_flag_set(m[k], PG_SWAPINPROG);
1111 bp->b_npages = j - i;
1113 pbgetvp(swapdev_vp, bp);
1115 mycpu->gd_cnt.v_swapin++;
1116 mycpu->gd_cnt.v_swappgsin += bp->b_npages;
1119 * We still hold the lock on mreq, and our automatic completion routine
1120 * does not remove it.
1123 vm_object_pip_add(mreq->object, bp->b_npages);
1124 lastpindex = m[j-1]->pindex;
1127 * perform the I/O. NOTE!!! bp cannot be considered valid after
1128 * this point because we automatically release it on completion.
1129 * Instead, we look at the one page we are interested in which we
1130 * still hold a lock on even through the I/O completion.
1132 * The other pages in our m[] array are also released on completion,
1133 * so we cannot assume they are valid anymore either.
1135 * NOTE: b_blkno is destroyed by the call to VOP_STRATEGY
1139 VOP_STRATEGY(bp->b_vp, bp);
1142 * wait for the page we want to complete. PG_SWAPINPROG is always
1143 * cleared on completion. If an I/O error occurs, SWAPBLK_NONE
1144 * is set in the meta-data.
1149 while ((mreq->flags & PG_SWAPINPROG) != 0) {
1150 vm_page_flag_set(mreq, PG_WANTED | PG_REFERENCED);
1151 mycpu->gd_cnt.v_intrans++;
1152 if (tsleep(mreq, 0, "swread", hz*20)) {
1154 "swap_pager: indefinite wait buffer: device:"
1155 " %s, blkno: %ld, size: %ld\n",
1156 devtoname(bp->b_dev), (long)bp->b_blkno,
1165 * mreq is left bussied after completion, but all the other pages
1166 * are freed. If we had an unrecoverable read error the page will
1170 if (mreq->valid != VM_PAGE_BITS_ALL) {
1171 return(VM_PAGER_ERROR);
1173 return(VM_PAGER_OK);
1177 * A final note: in a low swap situation, we cannot deallocate swap
1178 * and mark a page dirty here because the caller is likely to mark
1179 * the page clean when we return, causing the page to possibly revert
1180 * to all-zero's later.
1185 * swap_pager_putpages:
1187 * Assign swap (if necessary) and initiate I/O on the specified pages.
1189 * We support both OBJT_DEFAULT and OBJT_SWAP objects. DEFAULT objects
1190 * are automatically converted to SWAP objects.
1192 * In a low memory situation we may block in VOP_STRATEGY(), but the new
1193 * vm_page reservation system coupled with properly written VFS devices
1194 * should ensure that no low-memory deadlock occurs. This is an area
1197 * The parent has N vm_object_pip_add() references prior to
1198 * calling us and will remove references for rtvals[] that are
1199 * not set to VM_PAGER_PEND. We need to remove the rest on I/O
1202 * The parent has soft-busy'd the pages it passes us and will unbusy
1203 * those whos rtvals[] entry is not set to VM_PAGER_PEND on return.
1204 * We need to unbusy the rest on I/O completion.
1208 swap_pager_putpages(vm_object_t object, vm_page_t *m, int count, boolean_t sync,
1214 if (count && m[0]->object != object) {
1215 panic("swap_pager_getpages: object mismatch %p/%p",
1223 * Turn object into OBJT_SWAP
1224 * check for bogus sysops
1225 * force sync if not pageout process
1228 if (object->type != OBJT_SWAP)
1229 swp_pager_meta_build(object, 0, SWAPBLK_NONE);
1231 if (curthread != pagethread)
1237 * Update nsw parameters from swap_async_max sysctl values.
1238 * Do not let the sysop crash the machine with bogus numbers.
1241 if (swap_async_max != nsw_wcount_async_max) {
1248 if ((n = swap_async_max) > nswbuf / 2)
1255 * Adjust difference ( if possible ). If the current async
1256 * count is too low, we may not be able to make the adjustment
1260 n -= nsw_wcount_async_max;
1261 if (nsw_wcount_async + n >= 0) {
1262 nsw_wcount_async += n;
1263 nsw_wcount_async_max += n;
1264 wakeup(&nsw_wcount_async);
1272 * Assign swap blocks and issue I/O. We reallocate swap on the fly.
1273 * The page is left dirty until the pageout operation completes
1277 for (i = 0; i < count; i += n) {
1284 * Maximum I/O size is limited by a number of factors.
1287 n = min(BLIST_MAX_ALLOC, count - i);
1288 n = min(n, nsw_cluster_max);
1293 * Get biggest block of swap we can. If we fail, fall
1294 * back and try to allocate a smaller block. Don't go
1295 * overboard trying to allocate space if it would overly
1299 (blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE &&
1304 if (blk == SWAPBLK_NONE) {
1305 for (j = 0; j < n; ++j)
1306 rtvals[i+j] = VM_PAGER_FAIL;
1312 * The I/O we are constructing cannot cross a physical
1313 * disk boundry in the swap stripe. Note: we are still
1316 if ((blk ^ (blk + n)) & dmmax_mask) {
1317 j = ((blk + dmmax) & dmmax_mask) - blk;
1318 swp_pager_freeswapspace(blk + j, n - j);
1323 * All I/O parameters have been satisfied, build the I/O
1324 * request and assign the swap space.
1326 * NOTE: B_PAGING is set by pbgetvp()
1330 bp = getpbuf(&nsw_wcount_sync);
1331 bp->b_flags = B_CALL;
1333 bp = getpbuf(&nsw_wcount_async);
1334 bp->b_flags = B_CALL | B_ASYNC;
1336 bp->b_spc = NULL; /* not used, but NULL-out anyway */
1338 pmap_qenter((vm_offset_t)bp->b_data, &m[i], n);
1340 bp->b_bcount = PAGE_SIZE * n;
1341 bp->b_bufsize = PAGE_SIZE * n;
1344 pbgetvp(swapdev_vp, bp);
1346 for (j = 0; j < n; ++j) {
1347 vm_page_t mreq = m[i+j];
1349 swp_pager_meta_build(
1354 vm_page_dirty(mreq);
1355 rtvals[i+j] = VM_PAGER_OK;
1357 vm_page_flag_set(mreq, PG_SWAPINPROG);
1358 bp->b_pages[j] = mreq;
1362 * Must set dirty range for NFS to work.
1365 bp->b_dirtyend = bp->b_bcount;
1367 mycpu->gd_cnt.v_swapout++;
1368 mycpu->gd_cnt.v_swappgsout += bp->b_npages;
1369 swapdev_vp->v_numoutput++;
1376 * NOTE: b_blkno is destroyed by the call to VOP_STRATEGY
1379 if (sync == FALSE) {
1380 bp->b_iodone = swp_pager_async_iodone;
1382 VOP_STRATEGY(bp->b_vp, bp);
1384 for (j = 0; j < n; ++j)
1385 rtvals[i+j] = VM_PAGER_PEND;
1392 * NOTE: b_blkno is destroyed by the call to VOP_STRATEGY
1395 bp->b_iodone = swp_pager_sync_iodone;
1396 VOP_STRATEGY(bp->b_vp, bp);
1399 * Wait for the sync I/O to complete, then update rtvals.
1400 * We just set the rtvals[] to VM_PAGER_PEND so we can call
1401 * our async completion routine at the end, thus avoiding a
1406 while ((bp->b_flags & B_DONE) == 0) {
1407 tsleep(bp, 0, "swwrt", 0);
1410 for (j = 0; j < n; ++j)
1411 rtvals[i+j] = VM_PAGER_PEND;
1414 * Now that we are through with the bp, we can call the
1415 * normal async completion, which frees everything up.
1418 swp_pager_async_iodone(bp);
1425 * swap_pager_sync_iodone:
1427 * Completion routine for synchronous reads and writes from/to swap.
1428 * We just mark the bp is complete and wake up anyone waiting on it.
1430 * This routine may not block. This routine is called at splbio() or better.
1434 swp_pager_sync_iodone(struct buf *bp)
1436 bp->b_flags |= B_DONE;
1437 bp->b_flags &= ~B_ASYNC;
1442 * swp_pager_async_iodone:
1444 * Completion routine for asynchronous reads and writes from/to swap.
1445 * Also called manually by synchronous code to finish up a bp.
1447 * For READ operations, the pages are PG_BUSY'd. For WRITE operations,
1448 * the pages are vm_page_t->busy'd. For READ operations, we PG_BUSY
1449 * unbusy all pages except the 'main' request page. For WRITE
1450 * operations, we vm_page_t->busy'd unbusy all pages ( we can do this
1451 * because we marked them all VM_PAGER_PEND on return from putpages ).
1453 * This routine may not block.
1454 * This routine is called at splbio() or better
1456 * We up ourselves to splvm() as required for various vm_page related
1461 swp_pager_async_iodone(struct buf *bp)
1465 vm_object_t object = NULL;
1467 bp->b_flags |= B_DONE;
1473 if (bp->b_flags & B_ERROR) {
1475 "swap_pager: I/O error - %s failed; blkno %ld,"
1476 "size %ld, error %d\n",
1477 ((bp->b_flags & B_READ) ? "pagein" : "pageout"),
1485 * set object, raise to splvm().
1489 object = bp->b_pages[0]->object;
1493 * remove the mapping for kernel virtual
1496 pmap_qremove((vm_offset_t)bp->b_data, bp->b_npages);
1499 * cleanup pages. If an error occurs writing to swap, we are in
1500 * very serious trouble. If it happens to be a disk error, though,
1501 * we may be able to recover by reassigning the swap later on. So
1502 * in this case we remove the m->swapblk assignment for the page
1503 * but do not free it in the rlist. The errornous block(s) are thus
1504 * never reallocated as swap. Redirty the page and continue.
1507 for (i = 0; i < bp->b_npages; ++i) {
1508 vm_page_t m = bp->b_pages[i];
1510 vm_page_flag_clear(m, PG_SWAPINPROG);
1512 if (bp->b_flags & B_ERROR) {
1514 * If an error occurs I'd love to throw the swapblk
1515 * away without freeing it back to swapspace, so it
1516 * can never be used again. But I can't from an
1520 if (bp->b_flags & B_READ) {
1522 * When reading, reqpage needs to stay
1523 * locked for the parent, but all other
1524 * pages can be freed. We still want to
1525 * wakeup the parent waiting on the page,
1526 * though. ( also: pg_reqpage can be -1 and
1527 * not match anything ).
1529 * We have to wake specifically requested pages
1530 * up too because we cleared PG_SWAPINPROG and
1531 * someone may be waiting for that.
1533 * NOTE: for reads, m->dirty will probably
1534 * be overridden by the original caller of
1535 * getpages so don't play cute tricks here.
1537 * XXX IT IS NOT LEGAL TO FREE THE PAGE HERE
1538 * AS THIS MESSES WITH object->memq, and it is
1539 * not legal to mess with object->memq from an
1544 vm_page_flag_clear(m, PG_ZERO);
1546 if (i != bp->b_pager.pg_reqpage)
1551 * If i == bp->b_pager.pg_reqpage, do not wake
1552 * the page up. The caller needs to.
1556 * If a write error occurs, reactivate page
1557 * so it doesn't clog the inactive list,
1558 * then finish the I/O.
1561 vm_page_activate(m);
1562 vm_page_io_finish(m);
1564 } else if (bp->b_flags & B_READ) {
1566 * For read success, clear dirty bits. Nobody should
1567 * have this page mapped but don't take any chances,
1568 * make sure the pmap modify bits are also cleared.
1570 * NOTE: for reads, m->dirty will probably be
1571 * overridden by the original caller of getpages so
1572 * we cannot set them in order to free the underlying
1573 * swap in a low-swap situation. I don't think we'd
1574 * want to do that anyway, but it was an optimization
1575 * that existed in the old swapper for a time before
1576 * it got ripped out due to precisely this problem.
1578 * clear PG_ZERO in page.
1580 * If not the requested page then deactivate it.
1582 * Note that the requested page, reqpage, is left
1583 * busied, but we still have to wake it up. The
1584 * other pages are released (unbusied) by
1585 * vm_page_wakeup(). We do not set reqpage's
1586 * valid bits here, it is up to the caller.
1589 pmap_clear_modify(m);
1590 m->valid = VM_PAGE_BITS_ALL;
1592 vm_page_flag_clear(m, PG_ZERO);
1595 * We have to wake specifically requested pages
1596 * up too because we cleared PG_SWAPINPROG and
1597 * could be waiting for it in getpages. However,
1598 * be sure to not unbusy getpages specifically
1599 * requested page - getpages expects it to be
1602 if (i != bp->b_pager.pg_reqpage) {
1603 vm_page_deactivate(m);
1610 * For write success, clear the modify and dirty
1611 * status, then finish the I/O ( which decrements the
1612 * busy count and possibly wakes waiter's up ).
1614 pmap_clear_modify(m);
1616 vm_page_io_finish(m);
1617 if (!vm_page_count_severe() || !vm_page_try_to_cache(m))
1618 vm_page_protect(m, VM_PROT_READ);
1623 * adjust pip. NOTE: the original parent may still have its own
1624 * pip refs on the object.
1628 vm_object_pip_wakeupn(object, bp->b_npages);
1631 * release the physical I/O buffer
1636 ((bp->b_flags & B_READ) ? &nsw_rcount :
1637 ((bp->b_flags & B_ASYNC) ?
1646 /************************************************************************
1648 ************************************************************************
1650 * These routines manipulate the swap metadata stored in the
1651 * OBJT_SWAP object. All swp_*() routines must be called at
1652 * splvm() because swap can be freed up by the low level vm_page
1653 * code which might be called from interrupts beyond what splbio() covers.
1655 * Swap metadata is implemented with a global hash and not directly
1656 * linked into the object. Instead the object simply contains
1657 * appropriate tracking counters.
1661 * SWP_PAGER_HASH() - hash swap meta data
1663 * This is an inline helper function which hashes the swapblk given
1664 * the object and page index. It returns a pointer to a pointer
1665 * to the object, or a pointer to a NULL pointer if it could not
1668 * This routine must be called at splvm().
1671 static __inline struct swblock **
1672 swp_pager_hash(vm_object_t object, vm_pindex_t index)
1674 struct swblock **pswap;
1675 struct swblock *swap;
1677 index &= ~SWAP_META_MASK;
1678 pswap = &swhash[(index ^ (int)(intptr_t)object) & swhash_mask];
1680 while ((swap = *pswap) != NULL) {
1681 if (swap->swb_object == object &&
1682 swap->swb_index == index
1686 pswap = &swap->swb_hnext;
1692 * SWP_PAGER_META_BUILD() - add swap block to swap meta data for object
1694 * We first convert the object to a swap object if it is a default
1697 * The specified swapblk is added to the object's swap metadata. If
1698 * the swapblk is not valid, it is freed instead. Any previously
1699 * assigned swapblk is freed.
1701 * This routine must be called at splvm(), except when used to convert
1702 * an OBJT_DEFAULT object into an OBJT_SWAP object.
1707 swp_pager_meta_build(
1712 struct swblock *swap;
1713 struct swblock **pswap;
1716 * Convert default object to swap object if necessary
1719 if (object->type != OBJT_SWAP) {
1720 object->type = OBJT_SWAP;
1721 object->un_pager.swp.swp_bcount = 0;
1723 if (object->handle != NULL) {
1725 NOBJLIST(object->handle),
1731 &swap_pager_un_object_list,
1739 * Locate hash entry. If not found create, but if we aren't adding
1740 * anything just return. If we run out of space in the map we wait
1741 * and, since the hash table may have changed, retry.
1745 pswap = swp_pager_hash(object, index);
1747 if ((swap = *pswap) == NULL) {
1750 if (swapblk == SWAPBLK_NONE)
1753 swap = *pswap = zalloc(swap_zone);
1758 swap->swb_hnext = NULL;
1759 swap->swb_object = object;
1760 swap->swb_index = index & ~SWAP_META_MASK;
1761 swap->swb_count = 0;
1763 ++object->un_pager.swp.swp_bcount;
1765 for (i = 0; i < SWAP_META_PAGES; ++i)
1766 swap->swb_pages[i] = SWAPBLK_NONE;
1770 * Delete prior contents of metadata
1773 index &= SWAP_META_MASK;
1775 if (swap->swb_pages[index] != SWAPBLK_NONE) {
1776 swp_pager_freeswapspace(swap->swb_pages[index], 1);
1781 * Enter block into metadata
1784 swap->swb_pages[index] = swapblk;
1785 if (swapblk != SWAPBLK_NONE)
1790 * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
1792 * The requested range of blocks is freed, with any associated swap
1793 * returned to the swap bitmap.
1795 * This routine will free swap metadata structures as they are cleaned
1796 * out. This routine does *NOT* operate on swap metadata associated
1797 * with resident pages.
1799 * This routine must be called at splvm()
1803 swp_pager_meta_free(vm_object_t object, vm_pindex_t index, daddr_t count)
1805 if (object->type != OBJT_SWAP)
1809 struct swblock **pswap;
1810 struct swblock *swap;
1812 pswap = swp_pager_hash(object, index);
1814 if ((swap = *pswap) != NULL) {
1815 daddr_t v = swap->swb_pages[index & SWAP_META_MASK];
1817 if (v != SWAPBLK_NONE) {
1818 swp_pager_freeswapspace(v, 1);
1819 swap->swb_pages[index & SWAP_META_MASK] =
1821 if (--swap->swb_count == 0) {
1822 *pswap = swap->swb_hnext;
1823 zfree(swap_zone, swap);
1824 --object->un_pager.swp.swp_bcount;
1830 int n = SWAP_META_PAGES - (index & SWAP_META_MASK);
1838 * SWP_PAGER_META_FREE_ALL() - destroy all swap metadata associated with object
1840 * This routine locates and destroys all swap metadata associated with
1843 * This routine must be called at splvm()
1847 swp_pager_meta_free_all(vm_object_t object)
1851 if (object->type != OBJT_SWAP)
1854 while (object->un_pager.swp.swp_bcount) {
1855 struct swblock **pswap;
1856 struct swblock *swap;
1858 pswap = swp_pager_hash(object, index);
1859 if ((swap = *pswap) != NULL) {
1862 for (i = 0; i < SWAP_META_PAGES; ++i) {
1863 daddr_t v = swap->swb_pages[i];
1864 if (v != SWAPBLK_NONE) {
1866 swp_pager_freeswapspace(v, 1);
1869 if (swap->swb_count != 0)
1870 panic("swap_pager_meta_free_all: swb_count != 0");
1871 *pswap = swap->swb_hnext;
1872 zfree(swap_zone, swap);
1873 --object->un_pager.swp.swp_bcount;
1875 index += SWAP_META_PAGES;
1876 if (index > 0x20000000)
1877 panic("swp_pager_meta_free_all: failed to locate all swap meta blocks");
1882 * SWP_PAGER_METACTL() - misc control of swap and vm_page_t meta data.
1884 * This routine is capable of looking up, popping, or freeing
1885 * swapblk assignments in the swap meta data or in the vm_page_t.
1886 * The routine typically returns the swapblk being looked-up, or popped,
1887 * or SWAPBLK_NONE if the block was freed, or SWAPBLK_NONE if the block
1888 * was invalid. This routine will automatically free any invalid
1889 * meta-data swapblks.
1891 * It is not possible to store invalid swapblks in the swap meta data
1892 * (other then a literal 'SWAPBLK_NONE'), so we don't bother checking.
1894 * When acting on a busy resident page and paging is in progress, we
1895 * have to wait until paging is complete but otherwise can act on the
1898 * This routine must be called at splvm().
1900 * SWM_FREE remove and free swap block from metadata
1901 * SWM_POP remove from meta data but do not free.. pop it out
1910 struct swblock **pswap;
1911 struct swblock *swap;
1915 * The meta data only exists of the object is OBJT_SWAP
1916 * and even then might not be allocated yet.
1919 if (object->type != OBJT_SWAP)
1920 return(SWAPBLK_NONE);
1923 pswap = swp_pager_hash(object, index);
1925 if ((swap = *pswap) != NULL) {
1926 index &= SWAP_META_MASK;
1927 r1 = swap->swb_pages[index];
1929 if (r1 != SWAPBLK_NONE) {
1930 if (flags & SWM_FREE) {
1931 swp_pager_freeswapspace(r1, 1);
1934 if (flags & (SWM_FREE|SWM_POP)) {
1935 swap->swb_pages[index] = SWAPBLK_NONE;
1936 if (--swap->swb_count == 0) {
1937 *pswap = swap->swb_hnext;
1938 zfree(swap_zone, swap);
1939 --object->un_pager.swp.swp_bcount;