FreeBSD/Linux Kernel Cross Reference
sys/vm/swap_pager.c

     /*
      * (MPSAFE)
      *
      * Copyright (c) 1998-2010 The DragonFly Project.  All rights reserved.
      * 
      * This code is derived from software contributed to The DragonFly Project
      * by Matthew Dillon <dillon@backplane.com>
      * 
      * 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. Neither the name of The DragonFly Project 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 COPYRIGHT HOLDERS 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
     * COPYRIGHT HOLDERS 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.
     * 
     * 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. 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.
     *
     *                              New Swap System
     *                              Matthew Dillon
     *
     * Radix Bitmap 'blists'.
     *
     *      - The new swapper uses the new radix bitmap code.  This should scale
     *        to arbitrarily small or arbitrarily large swap spaces and an almost
     *        arbitrary degree of fragmentation.
     *
     * Features:
     *
     *      - on the fly reallocation of swap during putpages.  The new system
     *        does not try to keep previously allocated swap blocks for dirty
     *        pages.  
     *
     *      - on the fly deallocation of swap
     *
     *      - No more garbage collection required.  Unnecessarily allocated swap
     *        blocks only exist for dirty vm_page_t's now and these are already
     *        cycled (in a high-load system) by the pager.  We also do on-the-fly
     *        removal of invalidated swap blocks when a page is destroyed
     *        or renamed.
     *
     * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
     * @(#)swap_pager.c     8.9 (Berkeley) 3/21/94
     * $FreeBSD: src/sys/vm/swap_pager.c,v 1.130.2.12 2002/08/31 21:15:55 dillon Exp $
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/conf.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/sysctl.h>
   #include <sys/blist.h>
   #include <sys/lock.h>
   #include <sys/thread2.h>
   
   #include "opt_swap.h"
   #include <vm/vm.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>
   #include <vm/vm_zone.h>
   #include <vm/vnode_pager.h>
   
   #include <sys/buf2.h>
   #include <vm/vm_page2.h>
   
   #ifndef MAX_PAGEOUT_CLUSTER
   #define MAX_PAGEOUT_CLUSTER     SWB_NPAGES
   #endif
   
   #define SWM_FREE        0x02    /* free, period                 */
   #define SWM_POP         0x04    /* pop out                      */
   
   #define SWBIO_READ      0x01
   #define SWBIO_WRITE     0x02
   #define SWBIO_SYNC      0x04
   
   struct swfreeinfo {
           vm_object_t     object;
           vm_pindex_t     basei;
           vm_pindex_t     begi;
           vm_pindex_t     endi;   /* inclusive */
   };
   
   struct swswapoffinfo {
           vm_object_t     object;
           int             devidx;
           int             shared;
   };
   
   /*
    * vm_swap_size is in page-sized chunks now.  It was DEV_BSIZE'd chunks
    * in the old system.
    */
   
   int swap_pager_full;            /* swap space exhaustion (task killing) */
   int vm_swap_cache_use;
   int vm_swap_anon_use;
   static int vm_report_swap_allocs;
   
   static int swap_pager_almost_full; /* swap space exhaustion (w/ hysteresis)*/
   static int nsw_rcount;          /* free read buffers                    */
   static int nsw_wcount_sync;     /* limit write buffers / synchronous    */
   static int nsw_wcount_async;    /* limit write buffers / asynchronous   */
   static int nsw_wcount_async_max;/* assigned maximum                     */
   static int nsw_cluster_max;     /* maximum VOP I/O allowed              */
   
   struct blist *swapblist;
   static int swap_async_max = 4;  /* maximum in-progress async I/O's      */
   static int swap_burst_read = 0; /* allow burst reading */
   static swblk_t swapiterator;    /* linearize allocations */
   
   static struct spinlock swapbp_spin = SPINLOCK_INITIALIZER(&swapbp_spin);
   
   /* from vm_swap.c */
   extern struct vnode *swapdev_vp;
   extern struct swdevt *swdevt;
   extern int nswdev;
   
   #define BLK2DEVIDX(blk) (nswdev > 1 ? blk / dmmax % nswdev : 0)
   
   SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
           CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");
   SYSCTL_INT(_vm, OID_AUTO, swap_burst_read,
           CTLFLAG_RW, &swap_burst_read, 0, "Allow burst reads for pageins");
   
   SYSCTL_INT(_vm, OID_AUTO, swap_cache_use,
           CTLFLAG_RD, &vm_swap_cache_use, 0, "");
   SYSCTL_INT(_vm, OID_AUTO, swap_anon_use,
           CTLFLAG_RD, &vm_swap_anon_use, 0, "");
   SYSCTL_INT(_vm, OID_AUTO, swap_size,
           CTLFLAG_RD, &vm_swap_size, 0, "");
   SYSCTL_INT(_vm, OID_AUTO, report_swap_allocs,
           CTLFLAG_RW, &vm_report_swap_allocs, 0, "");
   
   vm_zone_t               swap_zone;
   
   /*
    * Red-Black tree for swblock entries
    *
    * The caller must hold vm_token
    */
   RB_GENERATE2(swblock_rb_tree, swblock, swb_entry, rb_swblock_compare,
                vm_pindex_t, swb_index);
   
   int
   rb_swblock_compare(struct swblock *swb1, struct swblock *swb2)
   {
           if (swb1->swb_index < swb2->swb_index)
                   return(-1);
           if (swb1->swb_index > swb2->swb_index)
                   return(1);
           return(0);
   }
   
   static
   int
   rb_swblock_scancmp(struct swblock *swb, void *data)
   {
           struct swfreeinfo *info = data;
   
           if (swb->swb_index < info->basei)
                   return(-1);
           if (swb->swb_index > info->endi)
                   return(1);
           return(0);
   }
   
   static
   int
   rb_swblock_condcmp(struct swblock *swb, void *data)
   {
           struct swfreeinfo *info = data;
   
           if (swb->swb_index < info->basei)
                   return(-1);
           return(0);
   }
   
   /*
    * pagerops for OBJT_SWAP - "swap pager".  Some ops are also global procedure
    * calls hooked from other parts of the VM system and do not appear here.
    * (see vm/swap_pager.h).
    */
   
   static void     swap_pager_dealloc (vm_object_t object);
   static int      swap_pager_getpage (vm_object_t, vm_page_t *, int);
   static void     swap_chain_iodone(struct bio *biox);
   
   struct pagerops swappagerops = {
           swap_pager_dealloc,     /* deallocate an OBJT_SWAP object       */
           swap_pager_getpage,     /* pagein                               */
           swap_pager_putpages,    /* pageout                              */
           swap_pager_haspage      /* get backing store status for page    */
   };
   
   /*
    * dmmax is in page-sized chunks with the new swap system.  It was
    * dev-bsized chunks in the old.  dmmax is always a power of 2.
    *
    * swap_*() routines are externally accessible.  swp_*() routines are
    * internal.
    */
   
   int dmmax;
   static int dmmax_mask;
   int nswap_lowat = 128;          /* in pages, swap_pager_almost_full warn */
   int nswap_hiwat = 512;          /* in pages, swap_pager_almost_full warn */
   
   static __inline void    swp_sizecheck (void);
   static void     swp_pager_async_iodone (struct bio *bio);
   
   /*
    * Swap bitmap functions
    */
   
   static __inline void    swp_pager_freeswapspace(vm_object_t object,
                                                   swblk_t blk, int npages);
   static __inline swblk_t swp_pager_getswapspace(vm_object_t object, int npages);
   
   /*
    * Metadata functions
    */
   
   static void swp_pager_meta_convert(vm_object_t);
   static void swp_pager_meta_build(vm_object_t, vm_pindex_t, swblk_t);
   static void swp_pager_meta_free(vm_object_t, vm_pindex_t, vm_pindex_t);
   static void swp_pager_meta_free_all(vm_object_t);
   static swblk_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
   
   /*
    * SWP_SIZECHECK() -    update swap_pager_full indication
    *      
    *      update the swap_pager_almost_full indication and warn when we are
    *      about to run out of swap space, using lowat/hiwat hysteresis.
    *
    *      Clear swap_pager_full ( task killing ) indication when lowat is met.
    *
    * No restrictions on call
    * This routine may not block.
    * SMP races are ok.
    */
   static __inline void
   swp_sizecheck(void)
   {
           if (vm_swap_size < nswap_lowat) {
                   if (swap_pager_almost_full == 0) {
                           kprintf("swap_pager: out of swap space\n");
                           swap_pager_almost_full = 1;
                   }
           } else {
                   swap_pager_full = 0;
                   if (vm_swap_size > nswap_hiwat)
                           swap_pager_almost_full = 0;
           }
   }
   
   /*
    * SWAP_PAGER_INIT() -  initialize the swap pager!
    *
    *      Expected to be started from system init.  NOTE:  This code is run 
    *      before much else so be careful what you depend on.  Most of the VM
    *      system has yet to be initialized at this point.
    *
    * Called from the low level boot code only.
    */
   static void
   swap_pager_init(void *arg __unused)
   {
           /*
            * Device Stripe, in PAGE_SIZE'd blocks
            */
           dmmax = SWB_NPAGES * 2;
           dmmax_mask = ~(dmmax - 1);
   }
   SYSINIT(vm_mem, SI_BOOT1_VM, SI_ORDER_THIRD, swap_pager_init, NULL)
   
   /*
    * SWAP_PAGER_SWAP_INIT() - swap pager initialization from pageout process
    *
    *      Expected to be started from pageout process once, prior to entering
    *      its main loop.
    *
    * Called from the low level boot code only.
    */
   void
   swap_pager_swap_init(void)
   {
           int n, n2;
   
           /*
            * Number of in-transit swap bp operations.  Don't
            * exhaust the pbufs completely.  Make sure we
            * initialize workable values (0 will work for hysteresis
            * but it isn't very efficient).
            *
            * The nsw_cluster_max is constrained by the number of pages an XIO
            * holds, i.e., (MAXPHYS/PAGE_SIZE) and our locally defined
            * MAX_PAGEOUT_CLUSTER.   Also be aware that swap ops are
            * constrained by the swap device interleave stripe size.
            *
            * Currently we hardwire nsw_wcount_async to 4.  This limit is 
            * designed to prevent other I/O from having high latencies due to
            * our pageout I/O.  The value 4 works well for one or two active swap
            * devices but is probably a little low if you have more.  Even so,
            * a higher value would probably generate only a limited improvement
            * with three or four active swap devices since the system does not
            * typically have to pageout at extreme bandwidths.   We will want
            * at least 2 per swap devices, and 4 is a pretty good value if you
            * have one NFS swap device due to the command/ack latency over NFS.
            * So it all works out pretty well.
            */
   
           nsw_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
   
           nsw_rcount = (nswbuf + 1) / 2;
           nsw_wcount_sync = (nswbuf + 3) / 4;
           nsw_wcount_async = 4;
           nsw_wcount_async_max = nsw_wcount_async;
   
           /*
            * The zone is dynamically allocated so generally size it to
            * maxswzone (32MB to 512MB of KVM).  Set a minimum size based
            * on physical memory of around 8x (each swblock can hold 16 pages).
            *
            * With the advent of SSDs (vs HDs) the practical (swap:memory) ratio
            * has increased dramatically.
            */
           n = vmstats.v_page_count / 2;
           if (maxswzone && n < maxswzone / sizeof(struct swblock))
                   n = maxswzone / sizeof(struct swblock);
           n2 = n;
   
           do {
                   swap_zone = zinit(
                           "SWAPMETA", 
                           sizeof(struct swblock), 
                           n,
                           ZONE_INTERRUPT, 
                           1);
                   if (swap_zone != NULL)
                           break;
                   /*
                    * if the allocation failed, try a zone two thirds the
                    * size of the previous attempt.
                    */
                   n -= ((n + 2) / 3);
           } while (n > 0);
   
           if (swap_zone == NULL)
                   panic("swap_pager_swap_init: swap_zone == NULL");
           if (n2 != n)
                   kprintf("Swap zone entries reduced from %d to %d.\n", n2, n);
   }
   
   /*
    * SWAP_PAGER_ALLOC() - allocate a new OBJT_SWAP VM object and instantiate
    *                      its metadata structures.
    *
    *      This routine is called from the mmap and fork code to create a new
    *      OBJT_SWAP object.  We do this by creating an OBJT_DEFAULT object
    *      and then converting it with swp_pager_meta_convert().
    *
    *      We only support unnamed objects.
    *
    * No restrictions.
    */
   vm_object_t
   swap_pager_alloc(void *handle, off_t size, vm_prot_t prot, off_t offset)
   {
           vm_object_t object;
   
           KKASSERT(handle == NULL);
           object = vm_object_allocate_hold(OBJT_DEFAULT,
                                            OFF_TO_IDX(offset + PAGE_MASK + size));
           swp_pager_meta_convert(object);
           vm_object_drop(object);
   
           return (object);
   }
   
   /*
    * SWAP_PAGER_DEALLOC() -       remove swap metadata from object
    *
    *      The swap backing for the object is destroyed.  The code is 
    *      designed such that we can reinstantiate it later, but this
    *      routine is typically called only when the entire object is
    *      about to be destroyed.
    *
    * The object must be locked or unreferenceable.
    * No other requirements.
    */
   static void
   swap_pager_dealloc(vm_object_t object)
   {
           vm_object_hold(object);
           vm_object_pip_wait(object, "swpdea");
   
           /*
            * Free all remaining metadata.  We only bother to free it from 
            * the swap meta data.  We do not attempt to free swapblk's still
            * associated with vm_page_t's for this object.  We do not care
            * if paging is still in progress on some objects.
            */
           swp_pager_meta_free_all(object);
           vm_object_drop(object);
   }
   
   /************************************************************************
    *                      SWAP PAGER BITMAP ROUTINES                      *
    ************************************************************************/
   
   /*
    * SWP_PAGER_GETSWAPSPACE() -   allocate raw swap space
    *
    *      Allocate swap for the requested number of pages.  The starting
    *      swap block number (a page index) is returned or SWAPBLK_NONE
    *      if the allocation failed.
    *
    *      Also has the side effect of advising that somebody made a mistake
    *      when they configured swap and didn't configure enough.
    *
    * The caller must hold the object.
    * This routine may not block.
    */
   static __inline swblk_t
   swp_pager_getswapspace(vm_object_t object, int npages)
   {
           swblk_t blk;
   
           lwkt_gettoken(&vm_token);
           blk = blist_allocat(swapblist, npages, swapiterator);
           if (blk == SWAPBLK_NONE)
                   blk = blist_allocat(swapblist, npages, 0);
           if (blk == SWAPBLK_NONE) {
                   if (swap_pager_full != 2) {
                           kprintf("swap_pager_getswapspace: failed alloc=%d\n",
                                   npages);
                           swap_pager_full = 2;
                           swap_pager_almost_full = 1;
                   }
           } else {
                   /* swapiterator = blk; disable for now, doesn't work well */
                   swapacctspace(blk, -npages);
                   if (object->type == OBJT_SWAP)
                           vm_swap_anon_use += npages;
                   else
                           vm_swap_cache_use += npages;
                   swp_sizecheck();
           }
           lwkt_reltoken(&vm_token);
           return(blk);
   }
   
   /*
    * SWP_PAGER_FREESWAPSPACE() -  free raw swap space 
    *
    *      This routine returns the specified swap blocks back to the bitmap.
    *
    *      Note:  This routine may not block (it could in the old swap code),
    *      and through the use of the new blist routines it does not block.
    *
    *      We must be called at splvm() to avoid races with bitmap frees from
    *      vm_page_remove() aka swap_pager_page_removed().
    *
    * This routine may not block.
    */
   
   static __inline void
   swp_pager_freeswapspace(vm_object_t object, swblk_t blk, int npages)
   {
           struct swdevt *sp = &swdevt[BLK2DEVIDX(blk)];
   
           lwkt_gettoken(&vm_token);
           sp->sw_nused -= npages;
           if (object->type == OBJT_SWAP)
                   vm_swap_anon_use -= npages;
           else
                   vm_swap_cache_use -= npages;
   
           if (sp->sw_flags & SW_CLOSING) {
                   lwkt_reltoken(&vm_token);
                   return;
           }
   
           blist_free(swapblist, blk, npages);
           vm_swap_size += npages;
           swp_sizecheck();
           lwkt_reltoken(&vm_token);
   }
   
   /*
    * SWAP_PAGER_FREESPACE() -     frees swap blocks associated with a page
    *                              range within an object.
    *
    *      This is a globally accessible routine.
    *
    *      This routine removes swapblk assignments from swap metadata.
    *
    *      The external callers of this routine typically have already destroyed 
    *      or renamed vm_page_t's associated with this range in the object so 
    *      we should be ok.
    *
    * No requirements.
    */
   void
   swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_pindex_t size)
   {
           vm_object_hold(object);
           swp_pager_meta_free(object, start, size);
           vm_object_drop(object);
   }
   
   /*
    * No requirements.
    */
   void
   swap_pager_freespace_all(vm_object_t object)
   {
           vm_object_hold(object);
           swp_pager_meta_free_all(object);
           vm_object_drop(object);
   }
   
   /*
    * This function conditionally frees swap cache swap starting at
    * (*basei) in the object.  (count) swap blocks will be nominally freed.
    * The actual number of blocks freed can be more or less than the
    * requested number.
    *
    * This function nominally returns the number of blocks freed.  However,
    * the actual number of blocks freed may be less then the returned value.
    * If the function is unable to exhaust the object or if it is able to
    * free (approximately) the requested number of blocks it returns
    * a value n > count.
    *
    * If we exhaust the object we will return a value n <= count.
    *
    * The caller must hold the object.
    *
    * WARNING!  If count == 0 then -1 can be returned as a degenerate case,
    *           callers should always pass a count value > 0.
    */
   static int swap_pager_condfree_callback(struct swblock *swap, void *data);
   
   int
   swap_pager_condfree(vm_object_t object, vm_pindex_t *basei, int count)
   {
           struct swfreeinfo info;
           int n;
           int t;
   
           ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
   
           info.object = object;
           info.basei = *basei;    /* skip up to this page index */
           info.begi = count;      /* max swap pages to destroy */
           info.endi = count * 8;  /* max swblocks to scan */
   
           swblock_rb_tree_RB_SCAN(&object->swblock_root, rb_swblock_condcmp,
                                   swap_pager_condfree_callback, &info);
           *basei = info.basei;
   
           /*
            * Take the higher difference swblocks vs pages
            */
           n = count - (int)info.begi;
           t = count * 8 - (int)info.endi;
           if (n < t)
                   n = t;
           if (n < 1)
                   n = 1;
           return(n);
   }
   
   /*
    * The idea is to free whole meta-block to avoid fragmenting
    * the swap space or disk I/O.  We only do this if NO VM pages
    * are present.
    *
    * We do not have to deal with clearing PG_SWAPPED in related VM
    * pages because there are no related VM pages.
    *
    * The caller must hold the object.
    */
   static int
   swap_pager_condfree_callback(struct swblock *swap, void *data)
   {
           struct swfreeinfo *info = data;
           vm_object_t object = info->object;
           int i;
   
           for (i = 0; i < SWAP_META_PAGES; ++i) {
                   if (vm_page_lookup(object, swap->swb_index + i))
                           break;
           }
           info->basei = swap->swb_index + SWAP_META_PAGES;
           if (i == SWAP_META_PAGES) {
                   info->begi -= swap->swb_count;
                   swap_pager_freespace(object, swap->swb_index, SWAP_META_PAGES);
           }
           --info->endi;
           if ((int)info->begi < 0 || (int)info->endi < 0)
                   return(-1);
           lwkt_yield();
           return(0);
   }
   
   /*
    * Called by vm_page_alloc() when a new VM page is inserted
    * into a VM object.  Checks whether swap has been assigned to
    * the page and sets PG_SWAPPED as necessary.
    *
    * No requirements.
    */
   void
   swap_pager_page_inserted(vm_page_t m)
   {
           if (m->object->swblock_count) {
                   vm_object_hold(m->object);
                   if (swp_pager_meta_ctl(m->object, m->pindex, 0) != SWAPBLK_NONE)
                           vm_page_flag_set(m, PG_SWAPPED);
                   vm_object_drop(m->object);
           }
   }
   
   /*
    * SWAP_PAGER_RESERVE() - reserve swap blocks in object
    *
    *      Assigns swap blocks to the specified range within the object.  The 
    *      swap blocks are not zerod.  Any previous swap assignment is destroyed.
    *
    *      Returns 0 on success, -1 on failure.
    *
    * The caller is responsible for avoiding races in the specified range.
    * No other requirements.
    */
   int
   swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
   {
           int n = 0;
           swblk_t blk = SWAPBLK_NONE;
           vm_pindex_t beg = start;        /* save start index */
   
           vm_object_hold(object);
   
           while (size) {
                   if (n == 0) {
                           n = BLIST_MAX_ALLOC;
                           while ((blk = swp_pager_getswapspace(object, n)) ==
                                  SWAPBLK_NONE)
                           {
                                   n >>= 1;
                                   if (n == 0) {
                                           swp_pager_meta_free(object, beg,
                                                               start - beg);
                                           vm_object_drop(object);
                                           return(-1);
                                   }
                           }
                   }
                   swp_pager_meta_build(object, start, blk);
                   --size;
                   ++start;
                   ++blk;
                   --n;
           }
           swp_pager_meta_free(object, start, n);
           vm_object_drop(object);
           return(0);
   }
   
   /*
    * SWAP_PAGER_COPY() -  copy blocks from source pager to destination pager
    *                      and destroy the source.
    *
    *      Copy any valid swapblks from the source to the destination.  In
    *      cases where both the source and destination have a valid swapblk,
    *      we keep the destination's.
    *
    *      This routine is allowed to block.  It may block allocating metadata
    *      indirectly through swp_pager_meta_build() or if paging is still in
    *      progress on the source. 
    *
    *      XXX vm_page_collapse() kinda expects us not to block because we 
    *      supposedly do not need to allocate memory, but for the moment we
    *      *may* have to get a little memory from the zone allocator, but
    *      it is taken from the interrupt memory.  We should be ok. 
    *
    *      The source object contains no vm_page_t's (which is just as well)
    *      The source object is of type OBJT_SWAP.
    *
    *      The source and destination objects must be held by the caller.
    */
   void
   swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
                   vm_pindex_t base_index, int destroysource)
   {
           vm_pindex_t i;
   
           ASSERT_LWKT_TOKEN_HELD(vm_object_token(srcobject));
           ASSERT_LWKT_TOKEN_HELD(vm_object_token(dstobject));
   
           /*
            * transfer source to destination.
            */
           for (i = 0; i < dstobject->size; ++i) {
                   swblk_t dstaddr;
   
                   /*
                    * Locate (without changing) the swapblk on the destination,
                    * unless it is invalid in which case free it silently, or
                    * if the destination is a resident page, in which case the
                    * source is thrown away.
                    */
                   dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
   
                   if (dstaddr == SWAPBLK_NONE) {
                           /*
                            * Destination has no swapblk and is not resident,
                            * copy source.
                            */
                           swblk_t srcaddr;
   
                           srcaddr = swp_pager_meta_ctl(srcobject,
                                                        base_index + i, SWM_POP);
   
                           if (srcaddr != SWAPBLK_NONE)
                                   swp_pager_meta_build(dstobject, i, srcaddr);
                   } else {
                           /*
                            * Destination has valid swapblk or it is represented
                            * by a resident page.  We destroy the sourceblock.
                            */
                           swp_pager_meta_ctl(srcobject, base_index + i, SWM_FREE);
                   }
           }
   
           /*
            * Free left over swap blocks in source.
            *
            * We have to revert the type to OBJT_DEFAULT so we do not accidently
            * double-remove the object from the swap queues.
            */
           if (destroysource) {
                   /*
                    * Reverting the type is not necessary, the caller is going
                    * to destroy srcobject directly, but I'm doing it here
                    * for consistency since we've removed the object from its
                    * queues.
                    */
                   swp_pager_meta_free_all(srcobject);
                   if (srcobject->type == OBJT_SWAP)
                           srcobject->type = OBJT_DEFAULT;
           }
   }
   
   /*
    * SWAP_PAGER_HASPAGE() -       determine if we have good backing store for
    *                              the requested page.
    *
    *      We determine whether good backing store exists for the requested
    *      page and return TRUE if it does, FALSE if it doesn't.
    *
    *      If TRUE, we also try to determine how much valid, contiguous backing
    *      store exists before and after the requested page within a reasonable
    *      distance.  We do not try to restrict it to the swap device stripe
    *      (that is handled in getpages/putpages).  It probably isn't worth
    *      doing here.
    *
    * No requirements.
    */
   boolean_t
   swap_pager_haspage(vm_object_t object, vm_pindex_t pindex)
   {
           swblk_t blk0;
   
           /*
            * do we have good backing store at the requested index ?
            */
           vm_object_hold(object);
           blk0 = swp_pager_meta_ctl(object, pindex, 0);
   
           if (blk0 == SWAPBLK_NONE) {
                   vm_object_drop(object);
                   return (FALSE);
           }
           vm_object_drop(object);
           return (TRUE);
   }
   
   /*
    * SWAP_PAGER_PAGE_UNSWAPPED() - remove swap backing store related to page
    *
    * This removes any associated swap backing store, whether valid or
    * not, from the page.  This operates on any VM object, not just OBJT_SWAP
    * objects.
    *
    * This routine is typically called when a page is made dirty, at
    * which point any associated swap can be freed.  MADV_FREE also
    * calls us in a special-case situation
    *
    * NOTE!!!  If the page is clean and the swap was valid, the caller
    * should make the page dirty before calling this routine.  This routine
    * does NOT change the m->dirty status of the page.  Also: MADV_FREE
    * depends on it.
    *
    * The page must be busied or soft-busied.
    * The caller can hold the object to avoid blocking, else we might block.
    * No other requirements.
    */
   void
   swap_pager_unswapped(vm_page_t m)
   {
           if (m->flags & PG_SWAPPED) {
                   vm_object_hold(m->object);
                   KKASSERT(m->flags & PG_SWAPPED);
                   swp_pager_meta_ctl(m->object, m->pindex, SWM_FREE);
                   vm_page_flag_clear(m, PG_SWAPPED);
                   vm_object_drop(m->object);
           }
   }
   
   /*
    * SWAP_PAGER_STRATEGY() - read, write, free blocks
    *
    * This implements a VM OBJECT strategy function using swap backing store.
    * This can operate on any VM OBJECT type, not necessarily just OBJT_SWAP
    * types.
    *
    * This is intended to be a cacheless interface (i.e. caching occurs at
    * higher levels), and is also used as a swap-based SSD cache for vnode
    * and device objects.
    *
    * All I/O goes directly to and from the swap device.
    *      
    * We currently attempt to run I/O synchronously or asynchronously as
    * the caller requests.  This isn't perfect because we loose error
    * sequencing when we run multiple ops in parallel to satisfy a request.
    * But this is swap, so we let it all hang out.
    *
    * No requirements.
    */
   void
   swap_pager_strategy(vm_object_t object, struct bio *bio)
   {
           struct buf *bp = bio->bio_buf;
           struct bio *nbio;
           vm_pindex_t start;
           vm_pindex_t biox_blkno = 0;
           int count;
           char *data;
           struct bio *biox;
           struct buf *bufx;
   #if 0
           struct bio_track *track;
   #endif
   
   #if 0
           /*
            * tracking for swapdev vnode I/Os
            */
           if (bp->b_cmd == BUF_CMD_READ)
                   track = &swapdev_vp->v_track_read;
           else
                   track = &swapdev_vp->v_track_write;
   #endif
   
           if (bp->b_bcount & PAGE_MASK) {
                   bp->b_error = EINVAL;
                   bp->b_flags |= B_ERROR | B_INVAL;
                   biodone(bio);
                   kprintf("swap_pager_strategy: bp %p offset %lld size %d, "
                           "not page bounded\n",
                           bp, (long long)bio->bio_offset, (int)bp->b_bcount);
                   return;
           }
   
           /*
            * Clear error indication, initialize page index, count, data pointer.
            */
           bp->b_error = 0;
           bp->b_flags &= ~B_ERROR;
           bp->b_resid = bp->b_bcount;
   
           start = (vm_pindex_t)(bio->bio_offset >> PAGE_SHIFT);
           count = howmany(bp->b_bcount, PAGE_SIZE);
           data = bp->b_data;
   
           /*
            * Deal with BUF_CMD_FREEBLKS
            */
           if (bp->b_cmd == BUF_CMD_FREEBLKS) {
                   /*
                    * FREE PAGE(s) - destroy underlying swap that is no longer
                    *                needed.
                    */
                   vm_object_hold(object);
                   swp_pager_meta_free(object, start, count);
                   vm_object_drop(object);
                   bp->b_resid = 0;
                   biodone(bio);
                   return;
           }
   
           /*
            * We need to be able to create a new cluster of I/O's.  We cannot
            * use the caller fields of the passed bio so push a new one.
            *
            * Because nbio is just a placeholder for the cluster links,
            * we can biodone() the original bio instead of nbio to make
            * things a bit more efficient.
            */
           nbio = push_bio(bio);
           nbio->bio_offset = bio->bio_offset;
           nbio->bio_caller_info1.cluster_head = NULL;
           nbio->bio_caller_info2.cluster_tail = NULL;
   
           biox = NULL;
           bufx = NULL;
   
           /*
            * Execute read or write
            */
           vm_object_hold(object);
   
           while (count > 0) {
                   swblk_t blk;
   
                   /*
                    * Obtain block.  If block not found and writing, allocate a
                    * new block and build it into the object.
                    */
                   blk = swp_pager_meta_ctl(object, start, 0);
                   if ((blk == SWAPBLK_NONE) && bp->b_cmd != BUF_CMD_READ) {
                           blk = swp_pager_getswapspace(object, 1);
                           if (blk == SWAPBLK_NONE) {
                                   bp->b_error = ENOMEM;
                                   bp->b_flags |= B_ERROR;
                                   break;
                           }
                          swp_pager_meta_build(object, start, blk);
                  }
                          
                  /*
                   * Do we have to flush our current collection?  Yes if:
                   *
                   *      - no swap block at this index
                   *      - swap block is not contiguous
                   *      - we cross a physical disk boundry in the
                   *        stripe.
                   */
                  if (
                      biox && (biox_blkno + btoc(bufx->b_bcount) != blk ||
                       ((biox_blkno ^ blk) & dmmax_mask)
                      )
                  ) {
                          if (bp->b_cmd == BUF_CMD_READ) {
                                  ++mycpu->gd_cnt.v_swapin;
                                  mycpu->gd_cnt.v_swappgsin += btoc(bufx->b_bcount);
                          } else {
                                  ++mycpu->gd_cnt.v_swapout;
                                  mycpu->gd_cnt.v_swappgsout += btoc(bufx->b_bcount);
                                  bufx->b_dirtyend = bufx->b_bcount;
                          }
  
                          /*
                           * Finished with this buf.
                           */
                          KKASSERT(bufx->b_bcount != 0);
                          if (bufx->b_cmd != BUF_CMD_READ)
                                  bufx->b_dirtyend = bufx->b_bcount;
                          biox = NULL;
                          bufx = NULL;
                  }
  
                  /*
                   * Add new swapblk to biox, instantiating biox if necessary.
                   * Zero-fill reads are able to take a shortcut.
                   */
                  if (blk == SWAPBLK_NONE) {
                          /*
                           * We can only get here if we are reading.  Since
                           * we are at splvm() we can safely modify b_resid,
                           * even if chain ops are in progress.
                           */
                          bzero(data, PAGE_SIZE);
                          bp->b_resid -= PAGE_SIZE;
                  } else {
                          if (biox == NULL) {
                                  /* XXX chain count > 4, wait to <= 4 */
  
                                  bufx = getpbuf(NULL);
                                  biox = &bufx->b_bio1;
                                  cluster_append(nbio, bufx);
                                  bufx->b_flags |= (bp->b_flags & B_ORDERED);
                                  bufx->b_cmd = bp->b_cmd;
                                  biox->bio_done = swap_chain_iodone;
                                  biox->bio_offset = (off_t)blk << PAGE_SHIFT;
                                  biox->bio_caller_info1.cluster_parent = nbio;
                                  biox_blkno = blk;
                                  bufx->b_bcount = 0;
                                  bufx->b_data = data;
                          }
                          bufx->b_bcount += PAGE_SIZE;
                  }
                  --count;
                  ++start;
                  data += PAGE_SIZE;
          }
  
          vm_object_drop(object);
  
          /*
           *  Flush out last buffer
           */
          if (biox) {
                  if (bufx->b_cmd == BUF_CMD_READ) {
                          ++mycpu->gd_cnt.v_swapin;
                          mycpu->gd_cnt.v_swappgsin += btoc(bufx->b_bcount);
                  } else {
                          ++mycpu->gd_cnt.v_swapout;
                          mycpu->gd_cnt.v_swappgsout += btoc(bufx->b_bcount);
                          bufx->b_dirtyend = bufx->b_bcount;
                  }
                  KKASSERT(bufx->b_bcount);
                  if (bufx->b_cmd != BUF_CMD_READ)
                          bufx->b_dirtyend = bufx->b_bcount;
                  /* biox, bufx = NULL */
          }
  
          /*
           * Now initiate all the I/O.  Be careful looping on our chain as
           * I/O's may complete while we are still initiating them.
           *
           * If the request is a 100% sparse read no bios will be present
           * and we just biodone() the buffer.
           */
          nbio->bio_caller_info2.cluster_tail = NULL;
          bufx = nbio->bio_caller_info1.cluster_head;
  
          if (bufx) {
                  while (bufx) {
                          biox = &bufx->b_bio1;
                          BUF_KERNPROC(bufx);
                          bufx = bufx->b_cluster_next;
                          vn_strategy(swapdev_vp, biox);
                  }
          } else {
                  biodone(bio);
          }
  
          /*
           * Completion of the cluster will also call biodone_chain(nbio).
           * We never call biodone(nbio) so we don't have to worry about
           * setting up a bio_done callback.  It's handled in the sub-IO.
           */
          /**/
  }
  
  /*
   * biodone callback
   *
   * No requirements.
   */
  static void
  swap_chain_iodone(struct bio *biox)
  {
          struct buf **nextp;
          struct buf *bufx;       /* chained sub-buffer */
          struct bio *nbio;       /* parent nbio with chain glue */
          struct buf *bp;         /* original bp associated with nbio */
          int chain_empty;
  
          bufx = biox->bio_buf;
          nbio = biox->bio_caller_info1.cluster_parent;
          bp = nbio->bio_buf;
  
          /*
           * Update the original buffer
           */
          KKASSERT(bp != NULL);
          if (bufx->b_flags & B_ERROR) {
                  atomic_set_int(&bufx->b_flags, B_ERROR);
                  bp->b_error = bufx->b_error;    /* race ok */
          } else if (bufx->b_resid != 0) {
                  atomic_set_int(&bufx->b_flags, B_ERROR);
                  bp->b_error = EINVAL;           /* race ok */
          } else {
                  atomic_subtract_int(&bp->b_resid, bufx->b_bcount);
          }
  
          /*
           * Remove us from the chain.
           */
          spin_lock(&swapbp_spin);
          nextp = &nbio->bio_caller_info1.cluster_head;
          while (*nextp != bufx) {
                  KKASSERT(*nextp != NULL);
                  nextp = &(*nextp)->b_cluster_next;
          }
          *nextp = bufx->b_cluster_next;
          chain_empty = (nbio->bio_caller_info1.cluster_head == NULL);
          spin_unlock(&swapbp_spin);
  
          /*
           * Clean up bufx.  If the chain is now empty we finish out
           * the parent.  Note that we may be racing other completions
           * so we must use the chain_empty status from above.
           */
          if (chain_empty) {
                  if (bp->b_resid != 0 && !(bp->b_flags & B_ERROR)) {
                          atomic_set_int(&bp->b_flags, B_ERROR);
                          bp->b_error = EINVAL;
                  }
                  biodone_chain(nbio);
          }
          relpbuf(bufx, NULL);
  }
  
  /*
   * SWAP_PAGER_GETPAGES() - bring page in from swap
   *
   * The requested page may have to be brought in from swap.  Calculate the
   * swap block and bring in additional pages if possible.  All pages must
   * have contiguous swap block assignments and reside in the same object.
   *
   * The caller has a single vm_object_pip_add() reference prior to
   * calling us and we should return with the same.
   *
   * The caller has BUSY'd the page.  We should return with (*mpp) left busy,
   * and any additinal pages unbusied.
   *
   * If the caller encounters a PG_RAM page it will pass it to us even though
   * it may be valid and dirty.  We cannot overwrite the page in this case!
   * The case is used to allow us to issue pure read-aheads.
   *
   * NOTE! XXX This code does not entirely pipeline yet due to the fact that
   *       the PG_RAM page is validated at the same time as mreq.  What we
   *       really need to do is issue a separate read-ahead pbuf.
   *
   * No requirements.
   */
  static int
  swap_pager_getpage(vm_object_t object, vm_page_t *mpp, int seqaccess)
  {
          struct buf *bp;
          struct bio *bio;
          vm_page_t mreq;
          vm_page_t m;
          vm_offset_t kva;
          swblk_t blk;
          int i;
          int j;
          int raonly;
          int error;
          u_int32_t flags;
          vm_page_t marray[XIO_INTERNAL_PAGES];
  
          mreq = *mpp;
  
          vm_object_hold(object);
          if (mreq->object != object) {
                  panic("swap_pager_getpages: object mismatch %p/%p", 
                      object, 
                      mreq->object
                  );
          }
  
          /*
           * We don't want to overwrite a fully valid page as it might be
           * dirty.  This case can occur when e.g. vm_fault hits a perfectly
           * valid page with PG_RAM set.
           *
           * In this case we see if the next page is a suitable page-in
           * candidate and if it is we issue read-ahead.  PG_RAM will be
           * set on the last page of the read-ahead to continue the pipeline.
           */
          if (mreq->valid == VM_PAGE_BITS_ALL) {
                  if (swap_burst_read == 0 || mreq->pindex + 1 >= object->size) {
                          vm_object_drop(object);
                          return(VM_PAGER_OK);
                  }
                  blk = swp_pager_meta_ctl(object, mreq->pindex + 1, 0);
                  if (blk == SWAPBLK_NONE) {
                          vm_object_drop(object);
                          return(VM_PAGER_OK);
                  }
                  m = vm_page_lookup_busy_try(object, mreq->pindex + 1,
                                              TRUE, &error);
                  if (error) {
                          vm_object_drop(object);
                          return(VM_PAGER_OK);
                  } else if (m == NULL) {
                          /*
                           * Use VM_ALLOC_QUICK to avoid blocking on cache
                           * page reuse.
                           */
                          m = vm_page_alloc(object, mreq->pindex + 1,
                                            VM_ALLOC_QUICK);
                          if (m == NULL) {
                                  vm_object_drop(object);
                                  return(VM_PAGER_OK);
                          }
                  } else {
                          if (m->valid) {
                                  vm_page_wakeup(m);
                                  vm_object_drop(object);
                                  return(VM_PAGER_OK);
                          }
                          vm_page_unqueue_nowakeup(m);
                  }
                  /* page is busy */
                  mreq = m;
                  raonly = 1;
          } else {
                  raonly = 0;
          }
  
          /*
           * Try to block-read contiguous pages from swap if sequential,
           * otherwise just read one page.  Contiguous pages from swap must
           * reside within a single device stripe because the I/O cannot be
           * broken up across multiple stripes.
           *
           * Note that blk and iblk can be SWAPBLK_NONE but the loop is
           * set up such that the case(s) are handled implicitly.
           */
          blk = swp_pager_meta_ctl(mreq->object, mreq->pindex, 0);
          marray[0] = mreq;
  
          for (i = 1; swap_burst_read &&
                      i < XIO_INTERNAL_PAGES &&
                      mreq->pindex + i < object->size; ++i) {
                  swblk_t iblk;
  
                  iblk = swp_pager_meta_ctl(object, mreq->pindex + i, 0);
                  if (iblk != blk + i)
                          break;
                  if ((blk ^ iblk) & dmmax_mask)
                          break;
                  m = vm_page_lookup_busy_try(object, mreq->pindex + i,
                                              TRUE, &error);
                  if (error) {
                          break;
                  } else if (m == NULL) {
                          /*
                           * Use VM_ALLOC_QUICK to avoid blocking on cache
                           * page reuse.
                           */
                          m = vm_page_alloc(object, mreq->pindex + i,
                                            VM_ALLOC_QUICK);
                          if (m == NULL)
                                  break;
                  } else {
                          if (m->valid) {
                                  vm_page_wakeup(m);
                                  break;
                          }
                          vm_page_unqueue_nowakeup(m);
                  }
                  /* page is busy */
                  marray[i] = m;
          }
          if (i > 1)
                  vm_page_flag_set(marray[i - 1], PG_RAM);
  
          /*
           * If mreq is the requested page and we have nothing to do return
           * VM_PAGER_FAIL.  If raonly is set mreq is just another read-ahead
           * page and must be cleaned up.
           */
          if (blk == SWAPBLK_NONE) {
                  KKASSERT(i == 1);
                  if (raonly) {
                          vnode_pager_freepage(mreq);
                          vm_object_drop(object);
                          return(VM_PAGER_OK);
                  } else {
                          vm_object_drop(object);
                          return(VM_PAGER_FAIL);
                  }
          }
  
          /*
           * map our page(s) into kva for input
           */
          bp = getpbuf_kva(&nsw_rcount);
          bio = &bp->b_bio1;
          kva = (vm_offset_t) bp->b_kvabase;
          bcopy(marray, bp->b_xio.xio_pages, i * sizeof(vm_page_t));
          pmap_qenter(kva, bp->b_xio.xio_pages, i);
  
          bp->b_data = (caddr_t)kva;
          bp->b_bcount = PAGE_SIZE * i;
          bp->b_xio.xio_npages = i;
          bio->bio_done = swp_pager_async_iodone;
          bio->bio_offset = (off_t)blk << PAGE_SHIFT;
          bio->bio_caller_info1.index = SWBIO_READ;
  
          /*
           * Set index.  If raonly set the index beyond the array so all
           * the pages are treated the same, otherwise the original mreq is
           * at index 0.
           */
          if (raonly)
                  bio->bio_driver_info = (void *)(intptr_t)i;
          else
                  bio->bio_driver_info = (void *)(intptr_t)0;
  
          for (j = 0; j < i; ++j)
                  vm_page_flag_set(bp->b_xio.xio_pages[j], PG_SWAPINPROG);
  
          mycpu->gd_cnt.v_swapin++;
          mycpu->gd_cnt.v_swappgsin += bp->b_xio.xio_npages;
  
          /*
           * We still hold the lock on mreq, and our automatic completion routine
           * does not remove it.
           */
          vm_object_pip_add(object, bp->b_xio.xio_npages);
  
          /*
           * perform the I/O.  NOTE!!!  bp cannot be considered valid after
           * this point because we automatically release it on completion.
           * Instead, we look at the one page we are interested in which we
           * still hold a lock on even through the I/O completion.
           *
           * The other pages in our m[] array are also released on completion,
           * so we cannot assume they are valid anymore either.
           */
          bp->b_cmd = BUF_CMD_READ;
          BUF_KERNPROC(bp);
          vn_strategy(swapdev_vp, bio);
  
          /*
           * Wait for the page we want to complete.  PG_SWAPINPROG is always
           * cleared on completion.  If an I/O error occurs, SWAPBLK_NONE
           * is set in the meta-data.
           *
           * If this is a read-ahead only we return immediately without
           * waiting for I/O.
           */
          if (raonly) {
                  vm_object_drop(object);
                  return(VM_PAGER_OK);
          }
  
          /*
           * Read-ahead includes originally requested page case.
           */
          for (;;) {
                  flags = mreq->flags;
                  cpu_ccfence();
                  if ((flags & PG_SWAPINPROG) == 0)
                          break;
                  tsleep_interlock(mreq, 0);
                  if (!atomic_cmpset_int(&mreq->flags, flags,
                                         flags | PG_WANTED | PG_REFERENCED)) {
                          continue;
                  }
                  mycpu->gd_cnt.v_intrans++;
                  if (tsleep(mreq, PINTERLOCKED, "swread", hz*20)) {
                          kprintf(
                              "swap_pager: indefinite wait buffer: "
                                  " offset: %lld, size: %ld\n",
                              (long long)bio->bio_offset,
                              (long)bp->b_bcount
                          );
                  }
          }
  
          /*
           * mreq is left bussied after completion, but all the other pages
           * are freed.  If we had an unrecoverable read error the page will
           * not be valid.
           */
          vm_object_drop(object);
          if (mreq->valid != VM_PAGE_BITS_ALL)
                  return(VM_PAGER_ERROR);
          else
                  return(VM_PAGER_OK);
  
          /*
           * A final note: in a low swap situation, we cannot deallocate swap
           * and mark a page dirty here because the caller is likely to mark
           * the page clean when we return, causing the page to possibly revert 
           * to all-zero's later.
           */
  }
  
  /*
   *      swap_pager_putpages: 
   *
   *      Assign swap (if necessary) and initiate I/O on the specified pages.
   *
   *      We support both OBJT_DEFAULT and OBJT_SWAP objects.  DEFAULT objects
   *      are automatically converted to SWAP objects.
   *
   *      In a low memory situation we may block in vn_strategy(), but the new 
   *      vm_page reservation system coupled with properly written VFS devices 
   *      should ensure that no low-memory deadlock occurs.  This is an area
   *      which needs work.
   *
   *      The parent has N vm_object_pip_add() references prior to
   *      calling us and will remove references for rtvals[] that are
   *      not set to VM_PAGER_PEND.  We need to remove the rest on I/O
   *      completion.
   *
   *      The parent has soft-busy'd the pages it passes us and will unbusy
   *      those whos rtvals[] entry is not set to VM_PAGER_PEND on return.
   *      We need to unbusy the rest on I/O completion.
   *
   * No requirements.
   */
  void
  swap_pager_putpages(vm_object_t object, vm_page_t *m, int count,
                      boolean_t sync, int *rtvals)
  {
          int i;
          int n = 0;
  
          vm_object_hold(object);
  
          if (count && m[0]->object != object) {
                  panic("swap_pager_getpages: object mismatch %p/%p", 
                      object, 
                      m[0]->object
                  );
          }
  
          /*
           * Step 1
           *
           * Turn object into OBJT_SWAP
           * check for bogus sysops
           * force sync if not pageout process
           */
          if (object->type == OBJT_DEFAULT) {
                  if (object->type == OBJT_DEFAULT)
                          swp_pager_meta_convert(object);
          }
  
          if (curthread != pagethread)
                  sync = TRUE;
  
          /*
           * Step 2
           *
           * Update nsw parameters from swap_async_max sysctl values.  
           * Do not let the sysop crash the machine with bogus numbers.
           */
          if (swap_async_max != nsw_wcount_async_max) {
                  int n;
  
                  /*
                   * limit range
                   */
                  if ((n = swap_async_max) > nswbuf / 2)
                          n = nswbuf / 2;
                  if (n < 1)
                          n = 1;
                  swap_async_max = n;
  
                  /*
                   * Adjust difference ( if possible ).  If the current async
                   * count is too low, we may not be able to make the adjustment
                   * at this time.
                   *
                   * vm_token needed for nsw_wcount sleep interlock
                   */
                  lwkt_gettoken(&vm_token);
                  n -= nsw_wcount_async_max;
                  if (nsw_wcount_async + n >= 0) {
                          nsw_wcount_async_max += n;
                          pbuf_adjcount(&nsw_wcount_async, n);
                  }
                  lwkt_reltoken(&vm_token);
          }
  
          /*
           * Step 3
           *
           * Assign swap blocks and issue I/O.  We reallocate swap on the fly.
           * The page is left dirty until the pageout operation completes
           * successfully.
           */
  
          for (i = 0; i < count; i += n) {
                  struct buf *bp;
                  struct bio *bio;
                  swblk_t blk;
                  int j;
  
                  /*
                   * Maximum I/O size is limited by a number of factors.
                   */
  
                  n = min(BLIST_MAX_ALLOC, count - i);
                  n = min(n, nsw_cluster_max);
  
                  lwkt_gettoken(&vm_token);
  
                  /*
                   * Get biggest block of swap we can.  If we fail, fall
                   * back and try to allocate a smaller block.  Don't go
                   * overboard trying to allocate space if it would overly
                   * fragment swap.
                   */
                  while (
                      (blk = swp_pager_getswapspace(object, n)) == SWAPBLK_NONE &&
                      n > 4
                  ) {
                          n >>= 1;
                  }
                  if (blk == SWAPBLK_NONE) {
                          for (j = 0; j < n; ++j)
                                  rtvals[i+j] = VM_PAGER_FAIL;
                          lwkt_reltoken(&vm_token);
                          continue;
                  }
                  if (vm_report_swap_allocs > 0) {
                          kprintf("swap_alloc %08jx,%d\n", (intmax_t)blk, n);
                          --vm_report_swap_allocs;
                  }
  
                  /*
                   * The I/O we are constructing cannot cross a physical
                   * disk boundry in the swap stripe.  Note: we are still
                   * at splvm().
                   */
                  if ((blk ^ (blk + n)) & dmmax_mask) {
                          j = ((blk + dmmax) & dmmax_mask) - blk;
                          swp_pager_freeswapspace(object, blk + j, n - j);
                          n = j;
                  }
  
                  /*
                   * All I/O parameters have been satisfied, build the I/O
                   * request and assign the swap space.
                   */
                  if (sync == TRUE)
                          bp = getpbuf_kva(&nsw_wcount_sync);
                  else
                          bp = getpbuf_kva(&nsw_wcount_async);
                  bio = &bp->b_bio1;
  
                  lwkt_reltoken(&vm_token);
  
                  pmap_qenter((vm_offset_t)bp->b_data, &m[i], n);
  
                  bp->b_bcount = PAGE_SIZE * n;
                  bio->bio_offset = (off_t)blk << PAGE_SHIFT;
  
                  for (j = 0; j < n; ++j) {
                          vm_page_t mreq = m[i+j];
  
                          swp_pager_meta_build(mreq->object, mreq->pindex,
                                               blk + j);
                          if (object->type == OBJT_SWAP)
                                  vm_page_dirty(mreq);
                          rtvals[i+j] = VM_PAGER_OK;
  
                          vm_page_flag_set(mreq, PG_SWAPINPROG);
                          bp->b_xio.xio_pages[j] = mreq;
                  }
                  bp->b_xio.xio_npages = n;
  
                  mycpu->gd_cnt.v_swapout++;
                  mycpu->gd_cnt.v_swappgsout += bp->b_xio.xio_npages;
  
                  bp->b_dirtyoff = 0;             /* req'd for NFS */
                  bp->b_dirtyend = bp->b_bcount;  /* req'd for NFS */
                  bp->b_cmd = BUF_CMD_WRITE;
                  bio->bio_caller_info1.index = SWBIO_WRITE;
  
                  /*
                   * asynchronous
                   */
                  if (sync == FALSE) {
                          bio->bio_done = swp_pager_async_iodone;
                          BUF_KERNPROC(bp);
                          vn_strategy(swapdev_vp, bio);
  
                          for (j = 0; j < n; ++j)
                                  rtvals[i+j] = VM_PAGER_PEND;
                          continue;
                  }
  
                  /*
                   * Issue synchrnously.
                   *
                   * Wait for the sync I/O to complete, then update rtvals.
                   * We just set the rtvals[] to VM_PAGER_PEND so we can call
                   * our async completion routine at the end, thus avoiding a
                   * double-free.
                   */
                  bio->bio_caller_info1.index |= SWBIO_SYNC;
                  bio->bio_done = biodone_sync;
                  bio->bio_flags |= BIO_SYNC;
                  vn_strategy(swapdev_vp, bio);
                  biowait(bio, "swwrt");
  
                  for (j = 0; j < n; ++j)
                          rtvals[i+j] = VM_PAGER_PEND;
  
                  /*
                   * Now that we are through with the bp, we can call the
                   * normal async completion, which frees everything up.
                   */
                  swp_pager_async_iodone(bio);
          }
          vm_object_drop(object);
  }
  
  /*
   * No requirements.
   */
  void
  swap_pager_newswap(void)
  {
          swp_sizecheck();
  }
  
  /*
   *      swp_pager_async_iodone:
   *
   *      Completion routine for asynchronous reads and writes from/to swap.
   *      Also called manually by synchronous code to finish up a bp.
   *
   *      For READ operations, the pages are PG_BUSY'd.  For WRITE operations, 
   *      the pages are vm_page_t->busy'd.  For READ operations, we PG_BUSY 
   *      unbusy all pages except the 'main' request page.  For WRITE 
   *      operations, we vm_page_t->busy'd unbusy all pages ( we can do this 
   *      because we marked them all VM_PAGER_PEND on return from putpages ).
   *
   *      This routine may not block.
   *
   * No requirements.
   */
  static void
  swp_pager_async_iodone(struct bio *bio)
  {
          struct buf *bp = bio->bio_buf;
          vm_object_t object = NULL;
          int i;
          int *nswptr;
  
          /*
           * report error
           */
          if (bp->b_flags & B_ERROR) {
                  kprintf(
                      "swap_pager: I/O error - %s failed; offset %lld,"
                          "size %ld, error %d\n",
                      ((bio->bio_caller_info1.index & SWBIO_READ) ?
                          "pagein" : "pageout"),
                      (long long)bio->bio_offset,
                      (long)bp->b_bcount,
                      bp->b_error
                  );
          }
  
          /*
           * set object, raise to splvm().
           */
          if (bp->b_xio.xio_npages)
                  object = bp->b_xio.xio_pages[0]->object;
  
          /*
           * remove the mapping for kernel virtual
           */
          pmap_qremove((vm_offset_t)bp->b_data, bp->b_xio.xio_npages);
  
          /*
           * cleanup pages.  If an error occurs writing to swap, we are in
           * very serious trouble.  If it happens to be a disk error, though,
           * we may be able to recover by reassigning the swap later on.  So
           * in this case we remove the m->swapblk assignment for the page 
           * but do not free it in the rlist.  The errornous block(s) are thus
           * never reallocated as swap.  Redirty the page and continue.
           */
          for (i = 0; i < bp->b_xio.xio_npages; ++i) {
                  vm_page_t m = bp->b_xio.xio_pages[i];
  
                  if (bp->b_flags & B_ERROR) {
                          /*
                           * If an error occurs I'd love to throw the swapblk
                           * away without freeing it back to swapspace, so it
                           * can never be used again.  But I can't from an 
                           * interrupt.
                           */
  
                          if (bio->bio_caller_info1.index & SWBIO_READ) {
                                  /*
                                   * When reading, reqpage needs to stay
                                   * locked for the parent, but all other
                                   * pages can be freed.  We still want to
                                   * wakeup the parent waiting on the page,
                                   * though.  ( also: pg_reqpage can be -1 and 
                                   * not match anything ).
                                   *
                                   * We have to wake specifically requested pages
                                   * up too because we cleared PG_SWAPINPROG and
                                   * someone may be waiting for that.
                                   *
                                   * NOTE: for reads, m->dirty will probably
                                   * be overridden by the original caller of
                                   * getpages so don't play cute tricks here.
                                   *
                                   * NOTE: We can't actually free the page from
                                   * here, because this is an interrupt.  It
                                   * is not legal to mess with object->memq
                                   * from an interrupt.  Deactivate the page
                                   * instead.
                                   */
  
                                  m->valid = 0;
                                  vm_page_flag_clear(m, PG_ZERO);
                                  vm_page_flag_clear(m, PG_SWAPINPROG);
  
                                  /*
                                   * bio_driver_info holds the requested page
                                   * index.
                                   */
                                  if (i != (int)(intptr_t)bio->bio_driver_info) {
                                          vm_page_deactivate(m);
                                          vm_page_wakeup(m);
                                  } else {
                                          vm_page_flash(m);
                                  }
                                  /*
                                   * If i == bp->b_pager.pg_reqpage, do not wake 
                                   * the page up.  The caller needs to.
                                   */
                          } else {
                                  /*
                                   * If a write error occurs remove the swap
                                   * assignment (note that PG_SWAPPED may or
                                   * may not be set depending on prior activity).
                                   *
                                   * Re-dirty OBJT_SWAP pages as there is no
                                   * other backing store, we can't throw the
                                   * page away.
                                   *
                                   * Non-OBJT_SWAP pages (aka swapcache) must
                                   * not be dirtied since they may not have
                                   * been dirty in the first place, and they
                                   * do have backing store (the vnode).
                                   */
                                  vm_page_busy_wait(m, FALSE, "swadpg");
                                  swp_pager_meta_ctl(m->object, m->pindex,
                                                     SWM_FREE);
                                  vm_page_flag_clear(m, PG_SWAPPED);
                                  if (m->object->type == OBJT_SWAP) {
                                          vm_page_dirty(m);
                                          vm_page_activate(m);
                                  }
                                  vm_page_flag_clear(m, PG_SWAPINPROG);
                                  vm_page_io_finish(m);
                                  vm_page_wakeup(m);
                          }
                  } else if (bio->bio_caller_info1.index & SWBIO_READ) {
                          /*
                           * NOTE: for reads, m->dirty will probably be 
                           * overridden by the original caller of getpages so
                           * we cannot set them in order to free the underlying
                           * swap in a low-swap situation.  I don't think we'd
                           * want to do that anyway, but it was an optimization
                           * that existed in the old swapper for a time before
                           * it got ripped out due to precisely this problem.
                           *
                           * clear PG_ZERO in page.
                           *
                           * If not the requested page then deactivate it.
                           *
                           * Note that the requested page, reqpage, is left
                           * busied, but we still have to wake it up.  The
                           * other pages are released (unbusied) by 
                           * vm_page_wakeup().  We do not set reqpage's
                           * valid bits here, it is up to the caller.
                           */
  
                          /* 
                           * NOTE: can't call pmap_clear_modify(m) from an
                           * interrupt thread, the pmap code may have to map
                           * non-kernel pmaps and currently asserts the case.
                           */
                          /*pmap_clear_modify(m);*/
                          m->valid = VM_PAGE_BITS_ALL;
                          vm_page_undirty(m);
                          vm_page_flag_clear(m, PG_ZERO | PG_SWAPINPROG);
                          vm_page_flag_set(m, PG_SWAPPED);
  
                          /*
                           * We have to wake specifically requested pages
                           * up too because we cleared PG_SWAPINPROG and
                           * could be waiting for it in getpages.  However,
                           * be sure to not unbusy getpages specifically
                           * requested page - getpages expects it to be 
                           * left busy.
                           *
                           * bio_driver_info holds the requested page
                           */
                          if (i != (int)(intptr_t)bio->bio_driver_info) {
                                  vm_page_deactivate(m);
                                  vm_page_wakeup(m);
                          } else {
                                  vm_page_flash(m);
                          }
                  } else {
                          /*
                           * Mark the page clean but do not mess with the
                           * pmap-layer's modified state.  That state should
                           * also be clear since the caller protected the
                           * page VM_PROT_READ, but allow the case.
                           *
                           * We are in an interrupt, avoid pmap operations.
                           *
                           * If we have a severe page deficit, deactivate the
                           * page.  Do not try to cache it (which would also
                           * involve a pmap op), because the page might still
                           * be read-heavy.
                           *
                           * When using the swap to cache clean vnode pages
                           * we do not mess with the page dirty bits.
                           */
                          vm_page_busy_wait(m, FALSE, "swadpg");
                          if (m->object->type == OBJT_SWAP)
                                  vm_page_undirty(m);
                          vm_page_flag_clear(m, PG_SWAPINPROG);
                          vm_page_flag_set(m, PG_SWAPPED);
                          if (vm_page_count_severe())
                                  vm_page_deactivate(m);
  #if 0
                          if (!vm_page_count_severe() || !vm_page_try_to_cache(m))
                                  vm_page_protect(m, VM_PROT_READ);
  #endif
                          vm_page_io_finish(m);
                          vm_page_wakeup(m);
                  }
          }
  
          /*
           * adjust pip.  NOTE: the original parent may still have its own
           * pip refs on the object.
           */
  
          if (object)
                  vm_object_pip_wakeup_n(object, bp->b_xio.xio_npages);
  
          /*
           * Release the physical I/O buffer.
           *
           * NOTE: Due to synchronous operations in the write case b_cmd may
           *       already be set to BUF_CMD_DONE and BIO_SYNC may have already
           *       been cleared.
           *
           * Use vm_token to interlock nsw_rcount/wcount wakeup?
           */
          lwkt_gettoken(&vm_token);
          if (bio->bio_caller_info1.index & SWBIO_READ)
                  nswptr = &nsw_rcount;
          else if (bio->bio_caller_info1.index & SWBIO_SYNC)
                  nswptr = &nsw_wcount_sync;
          else
                  nswptr = &nsw_wcount_async;
          bp->b_cmd = BUF_CMD_DONE;
          relpbuf(bp, nswptr);
          lwkt_reltoken(&vm_token);
  }
  
  /*
   * Fault-in a potentially swapped page and remove the swap reference.
   * (used by swapoff code)
   *
   * object must be held.
   */
  static __inline void
  swp_pager_fault_page(vm_object_t object, int *sharedp, vm_pindex_t pindex)
  {
          struct vnode *vp;
          vm_page_t m;
          int error;
  
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
  
          if (object->type == OBJT_VNODE) {
                  /*
                   * Any swap related to a vnode is due to swapcache.  We must
                   * vget() the vnode in case it is not active (otherwise
                   * vref() will panic).  Calling vm_object_page_remove() will
                   * ensure that any swap ref is removed interlocked with the
                   * page.  clean_only is set to TRUE so we don't throw away
                   * dirty pages.
                   */
                  vp = object->handle;
                  error = vget(vp, LK_SHARED | LK_RETRY | LK_CANRECURSE);
                  if (error == 0) {
                          vm_object_page_remove(object, pindex, pindex + 1, TRUE);
                          vput(vp);
                  }
          } else {
                  /*
                   * Otherwise it is a normal OBJT_SWAP object and we can
                   * fault the page in and remove the swap.
                   */
                  m = vm_fault_object_page(object, IDX_TO_OFF(pindex),
                                           VM_PROT_NONE,
                                           VM_FAULT_DIRTY | VM_FAULT_UNSWAP,
                                           sharedp, &error);
                  if (m)
                          vm_page_unhold(m);
          }
  }
  
  /*
   * This removes all swap blocks related to a particular device.  We have
   * to be careful of ripups during the scan.
   */
  static int swp_pager_swapoff_callback(struct swblock *swap, void *data);
  
  int
  swap_pager_swapoff(int devidx)
  {
          struct swswapoffinfo info;
          struct vm_object marker;
          vm_object_t object;
          int n;
  
          bzero(&marker, sizeof(marker));
          marker.type = OBJT_MARKER;
  
          for (n = 0; n < VMOBJ_HSIZE; ++n) {
                  lwkt_gettoken(&vmobj_tokens[n]);
                  TAILQ_INSERT_HEAD(&vm_object_lists[n], &marker, object_list);
  
                  while ((object = TAILQ_NEXT(&marker, object_list)) != NULL) {
                          if (object->type == OBJT_MARKER)
                                  goto skip;
                          if (object->type != OBJT_SWAP &&
                              object->type != OBJT_VNODE)
                                  goto skip;
                          vm_object_hold(object);
                          if (object->type != OBJT_SWAP &&
                              object->type != OBJT_VNODE) {
                                  vm_object_drop(object);
                                  goto skip;
                          }
                          info.object = object;
                          info.shared = 0;
                          info.devidx = devidx;
                          swblock_rb_tree_RB_SCAN(&object->swblock_root,
                                              NULL, swp_pager_swapoff_callback,
                                              &info);
                          vm_object_drop(object);
  skip:
                          if (object == TAILQ_NEXT(&marker, object_list)) {
                                  TAILQ_REMOVE(&vm_object_lists[n],
                                               &marker, object_list);
                                  TAILQ_INSERT_AFTER(&vm_object_lists[n], object,
                                                     &marker, object_list);
                          }
                  }
                  TAILQ_REMOVE(&vm_object_lists[n], &marker, object_list);
                  lwkt_reltoken(&vmobj_tokens[n]);
          }
  
          /*
           * If we fail to locate all swblocks we just fail gracefully and
           * do not bother to restore paging on the swap device.  If the
           * user wants to retry the user can retry.
           */
          if (swdevt[devidx].sw_nused)
                  return (1);
          else
                  return (0);
  }
  
  static
  int
  swp_pager_swapoff_callback(struct swblock *swap, void *data)
  {
          struct swswapoffinfo *info = data;
          vm_object_t object = info->object;
          vm_pindex_t index;
          swblk_t v;
          int i;
  
          index = swap->swb_index;
          for (i = 0; i < SWAP_META_PAGES; ++i) {
                  /*
                   * Make sure we don't race a dying object.  This will
                   * kill the scan of the object's swap blocks entirely.
                   */
                  if (object->flags & OBJ_DEAD)
                          return(-1);
  
                  /*
                   * Fault the page, which can obviously block.  If the swap
                   * structure disappears break out.
                   */
                  v = swap->swb_pages[i];
                  if (v != SWAPBLK_NONE && BLK2DEVIDX(v) == info->devidx) {
                          swp_pager_fault_page(object, &info->shared,
                                               swap->swb_index + i);
                          /* swap ptr might go away */
                          if (RB_LOOKUP(swblock_rb_tree,
                                        &object->swblock_root, index) != swap) {
                                  break;
                          }
                  }
          }
          return(0);
  }
  
  /************************************************************************
   *                              SWAP META DATA                          *
   ************************************************************************
   *
   *      These routines manipulate the swap metadata stored in the 
   *      OBJT_SWAP object.  All swp_*() routines must be called at
   *      splvm() because swap can be freed up by the low level vm_page
   *      code which might be called from interrupts beyond what splbio() covers.
   *
   *      Swap metadata is implemented with a global hash and not directly
   *      linked into the object.  Instead the object simply contains
   *      appropriate tracking counters.
   */
  
  /*
   * Lookup the swblock containing the specified swap block index.
   *
   * The caller must hold the object.
   */
  static __inline
  struct swblock *
  swp_pager_lookup(vm_object_t object, vm_pindex_t index)
  {
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
          index &= ~(vm_pindex_t)SWAP_META_MASK;
          return (RB_LOOKUP(swblock_rb_tree, &object->swblock_root, index));
  }
  
  /*
   * Remove a swblock from the RB tree.
   *
   * The caller must hold the object.
   */
  static __inline
  void
  swp_pager_remove(vm_object_t object, struct swblock *swap)
  {
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
          RB_REMOVE(swblock_rb_tree, &object->swblock_root, swap);
  }
  
  /*
   * Convert default object to swap object if necessary
   *
   * The caller must hold the object.
   */
  static void
  swp_pager_meta_convert(vm_object_t object)
  {
          if (object->type == OBJT_DEFAULT) {
                  object->type = OBJT_SWAP;
                  KKASSERT(object->swblock_count == 0);
          }
  }
  
  /*
   * SWP_PAGER_META_BUILD() -     add swap block to swap meta data for object
   *
   *      We first convert the object to a swap object if it is a default
   *      object.  Vnode objects do not need to be converted.
   *
   *      The specified swapblk is added to the object's swap metadata.  If
   *      the swapblk is not valid, it is freed instead.  Any previously
   *      assigned swapblk is freed.
   *
   * The caller must hold the object.
   */
  static void
  swp_pager_meta_build(vm_object_t object, vm_pindex_t index, swblk_t swapblk)
  {
          struct swblock *swap;
          struct swblock *oswap;
          vm_pindex_t v;
  
          KKASSERT(swapblk != SWAPBLK_NONE);
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
  
          /*
           * Convert object if necessary
           */
          if (object->type == OBJT_DEFAULT)
                  swp_pager_meta_convert(object);
          
          /*
           * Locate swblock.  If not found create, but if we aren't adding
           * anything just return.  If we run out of space in the map we wait
           * and, since the hash table may have changed, retry.
           */
  retry:
          swap = swp_pager_lookup(object, index);
  
          if (swap == NULL) {
                  int i;
  
                  swap = zalloc(swap_zone);
                  if (swap == NULL) {
                          vm_wait(0);
                          goto retry;
                  }
                  swap->swb_index = index & ~(vm_pindex_t)SWAP_META_MASK;
                  swap->swb_count = 0;
  
                  ++object->swblock_count;
  
                  for (i = 0; i < SWAP_META_PAGES; ++i)
                          swap->swb_pages[i] = SWAPBLK_NONE;
                  oswap = RB_INSERT(swblock_rb_tree, &object->swblock_root, swap);
                  KKASSERT(oswap == NULL);
          }
  
          /*
           * Delete prior contents of metadata.
           *
           * NOTE: Decrement swb_count after the freeing operation (which
           *       might block) to prevent racing destruction of the swblock.
           */
          index &= SWAP_META_MASK;
  
          while ((v = swap->swb_pages[index]) != SWAPBLK_NONE) {
                  swap->swb_pages[index] = SWAPBLK_NONE;
                  /* can block */
                  swp_pager_freeswapspace(object, v, 1);
                  --swap->swb_count;
                  --mycpu->gd_vmtotal.t_vm;
          }
  
          /*
           * Enter block into metadata
           */
          swap->swb_pages[index] = swapblk;
          if (swapblk != SWAPBLK_NONE) {
                  ++swap->swb_count;
                  ++mycpu->gd_vmtotal.t_vm;
          }
  }
  
  /*
   * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
   *
   *      The requested range of blocks is freed, with any associated swap 
   *      returned to the swap bitmap.
   *
   *      This routine will free swap metadata structures as they are cleaned 
   *      out.  This routine does *NOT* operate on swap metadata associated
   *      with resident pages.
   *
   * The caller must hold the object.
   */
  static int swp_pager_meta_free_callback(struct swblock *swb, void *data);
  
  static void
  swp_pager_meta_free(vm_object_t object, vm_pindex_t index, vm_pindex_t count)
  {
          struct swfreeinfo info;
  
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
  
          /*
           * Nothing to do
           */
          if (object->swblock_count == 0) {
                  KKASSERT(RB_EMPTY(&object->swblock_root));
                  return;
          }
          if (count == 0)
                  return;
  
          /*
           * Setup for RB tree scan.  Note that the pindex range can be huge
           * due to the 64 bit page index space so we cannot safely iterate.
           */
          info.object = object;
          info.basei = index & ~(vm_pindex_t)SWAP_META_MASK;
          info.begi = index;
          info.endi = index + count - 1;
          swblock_rb_tree_RB_SCAN(&object->swblock_root, rb_swblock_scancmp,
                                  swp_pager_meta_free_callback, &info);
  }
  
  /*
   * The caller must hold the object.
   */
  static
  int
  swp_pager_meta_free_callback(struct swblock *swap, void *data)
  {
          struct swfreeinfo *info = data;
          vm_object_t object = info->object;
          int index;
          int eindex;
  
          /*
           * Figure out the range within the swblock.  The wider scan may
           * return edge-case swap blocks when the start and/or end points
           * are in the middle of a block.
           */
          if (swap->swb_index < info->begi)
                  index = (int)info->begi & SWAP_META_MASK;
          else
                  index = 0;
  
          if (swap->swb_index + SWAP_META_PAGES > info->endi)
                  eindex = (int)info->endi & SWAP_META_MASK;
          else
                  eindex = SWAP_META_MASK;
  
          /*
           * Scan and free the blocks.  The loop terminates early
           * if (swap) runs out of blocks and could be freed.
           *
           * NOTE: Decrement swb_count after swp_pager_freeswapspace()
           *       to deal with a zfree race.
           */
          while (index <= eindex) {
                  swblk_t v = swap->swb_pages[index];
  
                  if (v != SWAPBLK_NONE) {
                          swap->swb_pages[index] = SWAPBLK_NONE;
                          /* can block */
                          swp_pager_freeswapspace(object, v, 1);
                          --mycpu->gd_vmtotal.t_vm;
                          if (--swap->swb_count == 0) {
                                  swp_pager_remove(object, swap);
                                  zfree(swap_zone, swap);
                                  --object->swblock_count;
                                  break;
                          }
                  }
                  ++index;
          }
  
          /* swap may be invalid here due to zfree above */
          lwkt_yield();
  
          return(0);
  }
  
  /*
   * SWP_PAGER_META_FREE_ALL() - destroy all swap metadata associated with object
   *
   *      This routine locates and destroys all swap metadata associated with
   *      an object.
   *
   * NOTE: Decrement swb_count after the freeing operation (which
   *       might block) to prevent racing destruction of the swblock.
   *
   * The caller must hold the object.
   */
  static void
  swp_pager_meta_free_all(vm_object_t object)
  {
          struct swblock *swap;
          int i;
  
          ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
  
          while ((swap = RB_ROOT(&object->swblock_root)) != NULL) {
                  swp_pager_remove(object, swap);
                  for (i = 0; i < SWAP_META_PAGES; ++i) {
                          swblk_t v = swap->swb_pages[i];
                          if (v != SWAPBLK_NONE) {
                                  /* can block */
                                  swp_pager_freeswapspace(object, v, 1);
                                  --swap->swb_count;
                                  --mycpu->gd_vmtotal.t_vm;
                          }
                  }
                  if (swap->swb_count != 0)
                          panic("swap_pager_meta_free_all: swb_count != 0");
                  zfree(swap_zone, swap);
                  --object->swblock_count;
                  lwkt_yield();
          }
          KKASSERT(object->swblock_count == 0);
  }
  
  /*
   * SWP_PAGER_METACTL() -  misc control of swap and vm_page_t meta data.
   *
   *      This routine is capable of looking up, popping, or freeing
   *      swapblk assignments in the swap meta data or in the vm_page_t.
   *      The routine typically returns the swapblk being looked-up, or popped,
   *      or SWAPBLK_NONE if the block was freed, or SWAPBLK_NONE if the block
   *      was invalid.  This routine will automatically free any invalid 
   *      meta-data swapblks.
   *
   *      It is not possible to store invalid swapblks in the swap meta data
   *      (other then a literal 'SWAPBLK_NONE'), so we don't bother checking.
   *
   *      When acting on a busy resident page and paging is in progress, we 
   *      have to wait until paging is complete but otherwise can act on the 
   *      busy page.
   *
   *      SWM_FREE        remove and free swap block from metadata
   *      SWM_POP         remove from meta data but do not free.. pop it out
   *
   * The caller must hold the object.
   */
  static swblk_t
  swp_pager_meta_ctl(vm_object_t object, vm_pindex_t index, int flags)
  {
          struct swblock *swap;
          swblk_t r1;
  
          if (object->swblock_count == 0)
                  return(SWAPBLK_NONE);
  
          r1 = SWAPBLK_NONE;
          swap = swp_pager_lookup(object, index);
  
          if (swap != NULL) {
                  index &= SWAP_META_MASK;
                  r1 = swap->swb_pages[index];
  
                  if (r1 != SWAPBLK_NONE) {
                          if (flags & (SWM_FREE|SWM_POP)) {
                                  swap->swb_pages[index] = SWAPBLK_NONE;
                                  --mycpu->gd_vmtotal.t_vm;
                                  if (--swap->swb_count == 0) {
                                          swp_pager_remove(object, swap);
                                          zfree(swap_zone, swap);
                                          --object->swblock_count;
                                  }
                          } 
                          /* swap ptr may be invalid */
                          if (flags & SWM_FREE) {
                                  swp_pager_freeswapspace(object, r1, 1);
                                  r1 = SWAPBLK_NONE;
                          }
                  }
                  /* swap ptr may be invalid */
          }
          return(r1);
  }

Cache object: c546f42a829052cb6896211a6e17ef88