The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/vm/swap_pager.c

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    1 /*
    2  * Copyright (c) 1998 Matthew Dillon,
    3  * Copyright (c) 1994 John S. Dyson
    4  * Copyright (c) 1990 University of Utah.
    5  * Copyright (c) 1982, 1986, 1989, 1993
    6  *      The Regents of the University of California.  All rights reserved.
    7  *
    8  * This code is derived from software contributed to Berkeley by
    9  * the Systems Programming Group of the University of Utah Computer
   10  * Science Department.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. All advertising materials mentioning features or use of this software
   21  *    must display the following acknowledgement:
   22  *      This product includes software developed by the University of
   23  *      California, Berkeley and its contributors.
   24  * 4. Neither the name of the University nor the names of its contributors
   25  *    may be used to endorse or promote products derived from this software
   26  *    without specific prior written permission.
   27  *
   28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   38  * SUCH DAMAGE.
   39  *
   40  *                              New Swap System
   41  *                              Matthew Dillon
   42  *
   43  * Radix Bitmap 'blists'.
   44  *
   45  *      - The new swapper uses the new radix bitmap code.  This should scale
   46  *        to arbitrarily small or arbitrarily large swap spaces and an almost
   47  *        arbitrary degree of fragmentation.
   48  *
   49  * Features:
   50  *
   51  *      - on the fly reallocation of swap during putpages.  The new system
   52  *        does not try to keep previously allocated swap blocks for dirty
   53  *        pages.  
   54  *
   55  *      - on the fly deallocation of swap
   56  *
   57  *      - No more garbage collection required.  Unnecessarily allocated swap
   58  *        blocks only exist for dirty vm_page_t's now and these are already
   59  *        cycled (in a high-load system) by the pager.  We also do on-the-fly
   60  *        removal of invalidated swap blocks when a page is destroyed
   61  *        or renamed.
   62  *
   63  * from: Utah $Hdr: swap_pager.c 1.4 91/04/30$
   64  *
   65  *      @(#)swap_pager.c        8.9 (Berkeley) 3/21/94
   66  *      @(#)vm_swap.c   8.5 (Berkeley) 2/17/94
   67  */
   68 
   69 #include <sys/cdefs.h>
   70 __FBSDID("$FreeBSD: releng/5.2/sys/vm/swap_pager.c 121854 2003-11-01 08:57:26Z alc $");
   71 
   72 #include "opt_mac.h"
   73 #include "opt_swap.h"
   74 #include "opt_vm.h"
   75 
   76 #include <sys/param.h>
   77 #include <sys/systm.h>
   78 #include <sys/conf.h>
   79 #include <sys/kernel.h>
   80 #include <sys/proc.h>
   81 #include <sys/bio.h>
   82 #include <sys/buf.h>
   83 #include <sys/disk.h>
   84 #include <sys/fcntl.h>
   85 #include <sys/mount.h>
   86 #include <sys/namei.h>
   87 #include <sys/vnode.h>
   88 #include <sys/mac.h>
   89 #include <sys/malloc.h>
   90 #include <sys/sysctl.h>
   91 #include <sys/sysproto.h>
   92 #include <sys/blist.h>
   93 #include <sys/lock.h>
   94 #include <sys/sx.h>
   95 #include <sys/vmmeter.h>
   96 
   97 #include <vm/vm.h>
   98 #include <vm/pmap.h>
   99 #include <vm/vm_map.h>
  100 #include <vm/vm_kern.h>
  101 #include <vm/vm_object.h>
  102 #include <vm/vm_page.h>
  103 #include <vm/vm_pager.h>
  104 #include <vm/vm_pageout.h>
  105 #include <vm/vm_param.h>
  106 #include <vm/swap_pager.h>
  107 #include <vm/vm_extern.h>
  108 #include <vm/uma.h>
  109 
  110 #include <geom/geom.h>
  111 
  112 /*
  113  * SWB_NPAGES must be a power of 2.  It may be set to 1, 2, 4, 8, or 16
  114  * pages per allocation.  We recommend you stick with the default of 8.
  115  * The 16-page limit is due to the radix code (kern/subr_blist.c).
  116  */
  117 #ifndef MAX_PAGEOUT_CLUSTER
  118 #define MAX_PAGEOUT_CLUSTER 16
  119 #endif
  120 
  121 #if !defined(SWB_NPAGES)
  122 #define SWB_NPAGES      MAX_PAGEOUT_CLUSTER
  123 #endif
  124 
  125 /*
  126  * Piecemeal swap metadata structure.  Swap is stored in a radix tree.
  127  *
  128  * If SWB_NPAGES is 8 and sizeof(char *) == sizeof(daddr_t), our radix
  129  * is basically 8.  Assuming PAGE_SIZE == 4096, one tree level represents
  130  * 32K worth of data, two levels represent 256K, three levels represent
  131  * 2 MBytes.   This is acceptable.
  132  *
  133  * Overall memory utilization is about the same as the old swap structure.
  134  */
  135 #define SWCORRECT(n) (sizeof(void *) * (n) / sizeof(daddr_t))
  136 #define SWAP_META_PAGES         (SWB_NPAGES * 2)
  137 #define SWAP_META_MASK          (SWAP_META_PAGES - 1)
  138 
  139 typedef int32_t swblk_t;        /*
  140                                  * swap offset.  This is the type used to
  141                                  * address the "virtual swap device" and
  142                                  * therefore the maximum swap space is
  143                                  * 2^32 pages.
  144                                  */
  145 
  146 struct swdevt;
  147 typedef void sw_strategy_t(struct buf *bp, struct swdevt *sw);
  148 typedef void sw_close_t(struct thread *td, struct swdevt *sw);
  149 
  150 /*
  151  * Swap device table
  152  */
  153 struct swdevt {
  154         int     sw_flags;
  155         int     sw_nblks;
  156         int     sw_used;
  157         udev_t  sw_udev;
  158         struct vnode *sw_vp;
  159         void    *sw_id;
  160         swblk_t sw_first;
  161         swblk_t sw_end;
  162         struct blist *sw_blist;
  163         TAILQ_ENTRY(swdevt)     sw_list;
  164         sw_strategy_t           *sw_strategy;
  165         sw_close_t              *sw_close;
  166 };
  167 
  168 #define SW_CLOSING      0x04
  169 
  170 struct swblock {
  171         struct swblock  *swb_hnext;
  172         vm_object_t     swb_object;
  173         vm_pindex_t     swb_index;
  174         int             swb_count;
  175         daddr_t         swb_pages[SWAP_META_PAGES];
  176 };
  177 
  178 static struct mtx sw_dev_mtx;
  179 static TAILQ_HEAD(, swdevt) swtailq = TAILQ_HEAD_INITIALIZER(swtailq);
  180 static struct swdevt *swdevhd;  /* Allocate from here next */
  181 static int nswapdev;            /* Number of swap devices */
  182 int swap_pager_avail;
  183 static int swdev_syscall_active = 0; /* serialize swap(on|off) */
  184 
  185 static void swapdev_strategy(struct buf *, struct swdevt *sw);
  186 
  187 #define SWM_FREE        0x02    /* free, period                 */
  188 #define SWM_POP         0x04    /* pop out                      */
  189 
  190 int swap_pager_full;            /* swap space exhaustion (task killing) */
  191 static int swap_pager_almost_full; /* swap space exhaustion (w/ hysteresis)*/
  192 static int nsw_rcount;          /* free read buffers                    */
  193 static int nsw_wcount_sync;     /* limit write buffers / synchronous    */
  194 static int nsw_wcount_async;    /* limit write buffers / asynchronous   */
  195 static int nsw_wcount_async_max;/* assigned maximum                     */
  196 static int nsw_cluster_max;     /* maximum VOP I/O allowed              */
  197 
  198 static struct swblock **swhash;
  199 static int swhash_mask;
  200 static struct mtx swhash_mtx;
  201 
  202 static int swap_async_max = 4;  /* maximum in-progress async I/O's      */
  203 static struct sx sw_alloc_sx;
  204 
  205 
  206 SYSCTL_INT(_vm, OID_AUTO, swap_async_max,
  207         CTLFLAG_RW, &swap_async_max, 0, "Maximum running async swap ops");
  208 
  209 /*
  210  * "named" and "unnamed" anon region objects.  Try to reduce the overhead
  211  * of searching a named list by hashing it just a little.
  212  */
  213 
  214 #define NOBJLISTS               8
  215 
  216 #define NOBJLIST(handle)        \
  217         (&swap_pager_object_list[((int)(intptr_t)handle >> 4) & (NOBJLISTS-1)])
  218 
  219 static struct mtx sw_alloc_mtx; /* protect list manipulation */ 
  220 static struct pagerlst  swap_pager_object_list[NOBJLISTS];
  221 static struct pagerlst  swap_pager_un_object_list;
  222 static uma_zone_t       swap_zone;
  223 
  224 /*
  225  * pagerops for OBJT_SWAP - "swap pager".  Some ops are also global procedure
  226  * calls hooked from other parts of the VM system and do not appear here.
  227  * (see vm/swap_pager.h).
  228  */
  229 static vm_object_t
  230                 swap_pager_alloc(void *handle, vm_ooffset_t size,
  231                                       vm_prot_t prot, vm_ooffset_t offset);
  232 static void     swap_pager_dealloc(vm_object_t object);
  233 static int      swap_pager_getpages(vm_object_t, vm_page_t *, int, int);
  234 static void     swap_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
  235 static boolean_t
  236                 swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after);
  237 static void     swap_pager_init(void);
  238 static void     swap_pager_unswapped(vm_page_t);
  239 static void     swap_pager_swapoff(struct swdevt *sp, int *sw_used);
  240 
  241 struct pagerops swappagerops = {
  242         .pgo_init =     swap_pager_init,        /* early system initialization of pager */
  243         .pgo_alloc =    swap_pager_alloc,       /* allocate an OBJT_SWAP object         */
  244         .pgo_dealloc =  swap_pager_dealloc,     /* deallocate an OBJT_SWAP object       */
  245         .pgo_getpages = swap_pager_getpages,    /* pagein                               */
  246         .pgo_putpages = swap_pager_putpages,    /* pageout                              */
  247         .pgo_haspage =  swap_pager_haspage,     /* get backing store status for page    */
  248         .pgo_pageunswapped = swap_pager_unswapped,      /* remove swap related to page          */
  249 };
  250 
  251 /*
  252  * dmmax is in page-sized chunks with the new swap system.  It was
  253  * dev-bsized chunks in the old.  dmmax is always a power of 2.
  254  *
  255  * swap_*() routines are externally accessible.  swp_*() routines are
  256  * internal.
  257  */
  258 static int dmmax;
  259 static int nswap_lowat = 128;   /* in pages, swap_pager_almost_full warn */
  260 static int nswap_hiwat = 512;   /* in pages, swap_pager_almost_full warn */
  261 
  262 SYSCTL_INT(_vm, OID_AUTO, dmmax,
  263         CTLFLAG_RD, &dmmax, 0, "Maximum size of a swap block");
  264 
  265 static void     swp_sizecheck(void);
  266 static void     swp_pager_sync_iodone(struct buf *bp);
  267 static void     swp_pager_async_iodone(struct buf *bp);
  268 static int      swapongeom(struct thread *, struct vnode *);
  269 static int      swaponvp(struct thread *, struct vnode *, u_long);
  270 
  271 /*
  272  * Swap bitmap functions
  273  */
  274 static void     swp_pager_freeswapspace(daddr_t blk, int npages);
  275 static daddr_t  swp_pager_getswapspace(int npages);
  276 
  277 /*
  278  * Metadata functions
  279  */
  280 static struct swblock **swp_pager_hash(vm_object_t object, vm_pindex_t index);
  281 static void swp_pager_meta_build(vm_object_t, vm_pindex_t, daddr_t);
  282 static void swp_pager_meta_free(vm_object_t, vm_pindex_t, daddr_t);
  283 static void swp_pager_meta_free_all(vm_object_t);
  284 static daddr_t swp_pager_meta_ctl(vm_object_t, vm_pindex_t, int);
  285 
  286 /*
  287  * SWP_SIZECHECK() -    update swap_pager_full indication
  288  *      
  289  *      update the swap_pager_almost_full indication and warn when we are
  290  *      about to run out of swap space, using lowat/hiwat hysteresis.
  291  *
  292  *      Clear swap_pager_full ( task killing ) indication when lowat is met.
  293  *
  294  *      No restrictions on call
  295  *      This routine may not block.
  296  *      This routine must be called at splvm()
  297  */
  298 static void
  299 swp_sizecheck(void)
  300 {
  301 
  302         if (swap_pager_avail < nswap_lowat) {
  303                 if (swap_pager_almost_full == 0) {
  304                         printf("swap_pager: out of swap space\n");
  305                         swap_pager_almost_full = 1;
  306                 }
  307         } else {
  308                 swap_pager_full = 0;
  309                 if (swap_pager_avail > nswap_hiwat)
  310                         swap_pager_almost_full = 0;
  311         }
  312 }
  313 
  314 /*
  315  * SWP_PAGER_HASH() -   hash swap meta data
  316  *
  317  *      This is an helper function which hashes the swapblk given
  318  *      the object and page index.  It returns a pointer to a pointer
  319  *      to the object, or a pointer to a NULL pointer if it could not
  320  *      find a swapblk.
  321  *
  322  *      This routine must be called at splvm().
  323  */
  324 static struct swblock **
  325 swp_pager_hash(vm_object_t object, vm_pindex_t index)
  326 {
  327         struct swblock **pswap;
  328         struct swblock *swap;
  329 
  330         index &= ~(vm_pindex_t)SWAP_META_MASK;
  331         pswap = &swhash[(index ^ (int)(intptr_t)object) & swhash_mask];
  332         while ((swap = *pswap) != NULL) {
  333                 if (swap->swb_object == object &&
  334                     swap->swb_index == index
  335                 ) {
  336                         break;
  337                 }
  338                 pswap = &swap->swb_hnext;
  339         }
  340         return (pswap);
  341 }
  342 
  343 /*
  344  * SWAP_PAGER_INIT() -  initialize the swap pager!
  345  *
  346  *      Expected to be started from system init.  NOTE:  This code is run 
  347  *      before much else so be careful what you depend on.  Most of the VM
  348  *      system has yet to be initialized at this point.
  349  */
  350 static void
  351 swap_pager_init(void)
  352 {
  353         /*
  354          * Initialize object lists
  355          */
  356         int i;
  357 
  358         for (i = 0; i < NOBJLISTS; ++i)
  359                 TAILQ_INIT(&swap_pager_object_list[i]);
  360         TAILQ_INIT(&swap_pager_un_object_list);
  361         mtx_init(&sw_alloc_mtx, "swap_pager list", NULL, MTX_DEF);
  362         mtx_init(&sw_dev_mtx, "swapdev", NULL, MTX_DEF);
  363 
  364         /*
  365          * Device Stripe, in PAGE_SIZE'd blocks
  366          */
  367         dmmax = SWB_NPAGES * 2;
  368 }
  369 
  370 /*
  371  * SWAP_PAGER_SWAP_INIT() - swap pager initialization from pageout process
  372  *
  373  *      Expected to be started from pageout process once, prior to entering
  374  *      its main loop.
  375  */
  376 void
  377 swap_pager_swap_init(void)
  378 {
  379         int n, n2;
  380 
  381         /*
  382          * Number of in-transit swap bp operations.  Don't
  383          * exhaust the pbufs completely.  Make sure we
  384          * initialize workable values (0 will work for hysteresis
  385          * but it isn't very efficient).
  386          *
  387          * The nsw_cluster_max is constrained by the bp->b_pages[]
  388          * array (MAXPHYS/PAGE_SIZE) and our locally defined
  389          * MAX_PAGEOUT_CLUSTER.   Also be aware that swap ops are
  390          * constrained by the swap device interleave stripe size.
  391          *
  392          * Currently we hardwire nsw_wcount_async to 4.  This limit is 
  393          * designed to prevent other I/O from having high latencies due to
  394          * our pageout I/O.  The value 4 works well for one or two active swap
  395          * devices but is probably a little low if you have more.  Even so,
  396          * a higher value would probably generate only a limited improvement
  397          * with three or four active swap devices since the system does not
  398          * typically have to pageout at extreme bandwidths.   We will want
  399          * at least 2 per swap devices, and 4 is a pretty good value if you
  400          * have one NFS swap device due to the command/ack latency over NFS.
  401          * So it all works out pretty well.
  402          */
  403         nsw_cluster_max = min((MAXPHYS/PAGE_SIZE), MAX_PAGEOUT_CLUSTER);
  404 
  405         mtx_lock(&pbuf_mtx);
  406         nsw_rcount = (nswbuf + 1) / 2;
  407         nsw_wcount_sync = (nswbuf + 3) / 4;
  408         nsw_wcount_async = 4;
  409         nsw_wcount_async_max = nsw_wcount_async;
  410         mtx_unlock(&pbuf_mtx);
  411 
  412         /*
  413          * Initialize our zone.  Right now I'm just guessing on the number
  414          * we need based on the number of pages in the system.  Each swblock
  415          * can hold 16 pages, so this is probably overkill.  This reservation
  416          * is typically limited to around 32MB by default.
  417          */
  418         n = cnt.v_page_count / 2;
  419         if (maxswzone && n > maxswzone / sizeof(struct swblock))
  420                 n = maxswzone / sizeof(struct swblock);
  421         n2 = n;
  422         swap_zone = uma_zcreate("SWAPMETA", sizeof(struct swblock), NULL, NULL,
  423             NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE | UMA_ZONE_VM);
  424         do {
  425                 if (uma_zone_set_obj(swap_zone, NULL, n))
  426                         break;
  427                 /*
  428                  * if the allocation failed, try a zone two thirds the
  429                  * size of the previous attempt.
  430                  */
  431                 n -= ((n + 2) / 3);
  432         } while (n > 0);
  433         if (swap_zone == NULL)
  434                 panic("failed to create swap_zone.");
  435         if (n2 != n)
  436                 printf("Swap zone entries reduced from %d to %d.\n", n2, n);
  437         n2 = n;
  438 
  439         /*
  440          * Initialize our meta-data hash table.  The swapper does not need to
  441          * be quite as efficient as the VM system, so we do not use an 
  442          * oversized hash table.
  443          *
  444          *      n:              size of hash table, must be power of 2
  445          *      swhash_mask:    hash table index mask
  446          */
  447         for (n = 1; n < n2 / 8; n *= 2)
  448                 ;
  449         swhash = malloc(sizeof(struct swblock *) * n, M_VMPGDATA, M_WAITOK | M_ZERO);
  450         swhash_mask = n - 1;
  451         mtx_init(&swhash_mtx, "swap_pager swhash", NULL, MTX_DEF);
  452 }
  453 
  454 /*
  455  * SWAP_PAGER_ALLOC() - allocate a new OBJT_SWAP VM object and instantiate
  456  *                      its metadata structures.
  457  *
  458  *      This routine is called from the mmap and fork code to create a new
  459  *      OBJT_SWAP object.  We do this by creating an OBJT_DEFAULT object
  460  *      and then converting it with swp_pager_meta_build().
  461  *
  462  *      This routine may block in vm_object_allocate() and create a named
  463  *      object lookup race, so we must interlock.   We must also run at
  464  *      splvm() for the object lookup to handle races with interrupts, but
  465  *      we do not have to maintain splvm() in between the lookup and the
  466  *      add because (I believe) it is not possible to attempt to create
  467  *      a new swap object w/handle when a default object with that handle
  468  *      already exists.
  469  *
  470  * MPSAFE
  471  */
  472 static vm_object_t
  473 swap_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
  474                  vm_ooffset_t offset)
  475 {
  476         vm_object_t object;
  477 
  478         mtx_lock(&Giant);
  479         if (handle) {
  480                 /*
  481                  * Reference existing named region or allocate new one.  There
  482                  * should not be a race here against swp_pager_meta_build()
  483                  * as called from vm_page_remove() in regards to the lookup
  484                  * of the handle.
  485                  */
  486                 sx_xlock(&sw_alloc_sx);
  487                 object = vm_pager_object_lookup(NOBJLIST(handle), handle);
  488 
  489                 if (object != NULL) {
  490                         vm_object_reference(object);
  491                 } else {
  492                         object = vm_object_allocate(OBJT_DEFAULT,
  493                                 OFF_TO_IDX(offset + PAGE_MASK + size));
  494                         object->handle = handle;
  495 
  496                         VM_OBJECT_LOCK(object);
  497                         swp_pager_meta_build(object, 0, SWAPBLK_NONE);
  498                         VM_OBJECT_UNLOCK(object);
  499                 }
  500                 sx_xunlock(&sw_alloc_sx);
  501         } else {
  502                 object = vm_object_allocate(OBJT_DEFAULT,
  503                         OFF_TO_IDX(offset + PAGE_MASK + size));
  504 
  505                 VM_OBJECT_LOCK(object);
  506                 swp_pager_meta_build(object, 0, SWAPBLK_NONE);
  507                 VM_OBJECT_UNLOCK(object);
  508         }
  509         mtx_unlock(&Giant);
  510         return (object);
  511 }
  512 
  513 /*
  514  * SWAP_PAGER_DEALLOC() -       remove swap metadata from object
  515  *
  516  *      The swap backing for the object is destroyed.  The code is 
  517  *      designed such that we can reinstantiate it later, but this
  518  *      routine is typically called only when the entire object is
  519  *      about to be destroyed.
  520  *
  521  *      This routine may block, but no longer does. 
  522  *
  523  *      The object must be locked or unreferenceable.
  524  */
  525 static void
  526 swap_pager_dealloc(vm_object_t object)
  527 {
  528         int s;
  529 
  530         /*
  531          * Remove from list right away so lookups will fail if we block for
  532          * pageout completion.
  533          */
  534         mtx_lock(&sw_alloc_mtx);
  535         if (object->handle == NULL) {
  536                 TAILQ_REMOVE(&swap_pager_un_object_list, object, pager_object_list);
  537         } else {
  538                 TAILQ_REMOVE(NOBJLIST(object->handle), object, pager_object_list);
  539         }
  540         mtx_unlock(&sw_alloc_mtx);
  541 
  542         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  543         vm_object_pip_wait(object, "swpdea");
  544 
  545         /*
  546          * Free all remaining metadata.  We only bother to free it from 
  547          * the swap meta data.  We do not attempt to free swapblk's still
  548          * associated with vm_page_t's for this object.  We do not care
  549          * if paging is still in progress on some objects.
  550          */
  551         s = splvm();
  552         swp_pager_meta_free_all(object);
  553         splx(s);
  554 }
  555 
  556 /************************************************************************
  557  *                      SWAP PAGER BITMAP ROUTINES                      *
  558  ************************************************************************/
  559 
  560 /*
  561  * SWP_PAGER_GETSWAPSPACE() -   allocate raw swap space
  562  *
  563  *      Allocate swap for the requested number of pages.  The starting
  564  *      swap block number (a page index) is returned or SWAPBLK_NONE
  565  *      if the allocation failed.
  566  *
  567  *      Also has the side effect of advising that somebody made a mistake
  568  *      when they configured swap and didn't configure enough.
  569  *
  570  *      Must be called at splvm() to avoid races with bitmap frees from
  571  *      vm_page_remove() aka swap_pager_page_removed().
  572  *
  573  *      This routine may not block
  574  *      This routine must be called at splvm().
  575  *
  576  *      We allocate in round-robin fashion from the configured devices.
  577  */
  578 static daddr_t
  579 swp_pager_getswapspace(int npages)
  580 {
  581         daddr_t blk;
  582         struct swdevt *sp;
  583         int i;
  584 
  585         blk = SWAPBLK_NONE;
  586         mtx_lock(&sw_dev_mtx);
  587         sp = swdevhd;
  588         for (i = 0; i < nswapdev; i++) {
  589                 if (sp == NULL)
  590                         sp = TAILQ_FIRST(&swtailq);
  591                 if (!(sp->sw_flags & SW_CLOSING)) {
  592                         blk = blist_alloc(sp->sw_blist, npages);
  593                         if (blk != SWAPBLK_NONE) {
  594                                 blk += sp->sw_first;
  595                                 sp->sw_used += npages;
  596                                 swap_pager_avail -= npages;
  597                                 swp_sizecheck();
  598                                 swdevhd = TAILQ_NEXT(sp, sw_list);
  599                                 goto done;
  600                         }
  601                 }
  602                 sp = TAILQ_NEXT(sp, sw_list);
  603         }
  604         if (swap_pager_full != 2) {
  605                 printf("swap_pager_getswapspace(%d): failed\n", npages);
  606                 swap_pager_full = 2;
  607                 swap_pager_almost_full = 1;
  608         }
  609         swdevhd = NULL;
  610 done:
  611         mtx_unlock(&sw_dev_mtx);
  612         return (blk);
  613 }
  614 
  615 static struct swdevt *
  616 swp_pager_find_dev(daddr_t blk)
  617 {
  618         struct swdevt *sp;
  619 
  620         mtx_lock(&sw_dev_mtx);
  621         TAILQ_FOREACH(sp, &swtailq, sw_list) {
  622                 if (blk >= sp->sw_first && blk < sp->sw_end) {
  623                         mtx_unlock(&sw_dev_mtx);
  624                         return (sp);
  625                 }
  626         }
  627         panic("Swapdev not found");
  628 }
  629         
  630 static void
  631 swp_pager_strategy(struct buf *bp)
  632 {
  633         struct swdevt *sp;
  634 
  635         mtx_lock(&sw_dev_mtx);
  636         TAILQ_FOREACH(sp, &swtailq, sw_list) {
  637                 if (bp->b_blkno >= sp->sw_first && bp->b_blkno < sp->sw_end) {
  638                         mtx_unlock(&sw_dev_mtx);
  639                         sp->sw_strategy(bp, sp);
  640                         return;
  641                 }
  642         }
  643         panic("Swapdev not found");
  644 }
  645         
  646 
  647 /*
  648  * SWP_PAGER_FREESWAPSPACE() -  free raw swap space 
  649  *
  650  *      This routine returns the specified swap blocks back to the bitmap.
  651  *
  652  *      Note:  This routine may not block (it could in the old swap code),
  653  *      and through the use of the new blist routines it does not block.
  654  *
  655  *      We must be called at splvm() to avoid races with bitmap frees from
  656  *      vm_page_remove() aka swap_pager_page_removed().
  657  *
  658  *      This routine may not block
  659  *      This routine must be called at splvm().
  660  */
  661 static void
  662 swp_pager_freeswapspace(daddr_t blk, int npages)
  663 {
  664         struct swdevt *sp;
  665 
  666         mtx_lock(&sw_dev_mtx);
  667         TAILQ_FOREACH(sp, &swtailq, sw_list) {
  668                 if (blk >= sp->sw_first && blk < sp->sw_end) {
  669                         sp->sw_used -= npages;
  670                         /*
  671                          * If we are attempting to stop swapping on
  672                          * this device, we don't want to mark any
  673                          * blocks free lest they be reused.  
  674                          */
  675                         if ((sp->sw_flags & SW_CLOSING) == 0) {
  676                                 blist_free(sp->sw_blist, blk - sp->sw_first,
  677                                     npages);
  678                                 swap_pager_avail += npages;
  679                                 swp_sizecheck();
  680                         }
  681                         mtx_unlock(&sw_dev_mtx);
  682                         return;
  683                 }
  684         }
  685         panic("Swapdev not found");
  686 }
  687 
  688 /*
  689  * SWAP_PAGER_FREESPACE() -     frees swap blocks associated with a page
  690  *                              range within an object.
  691  *
  692  *      This is a globally accessible routine.
  693  *
  694  *      This routine removes swapblk assignments from swap metadata.
  695  *
  696  *      The external callers of this routine typically have already destroyed 
  697  *      or renamed vm_page_t's associated with this range in the object so 
  698  *      we should be ok.
  699  *
  700  *      This routine may be called at any spl.  We up our spl to splvm temporarily
  701  *      in order to perform the metadata removal.
  702  */
  703 void
  704 swap_pager_freespace(vm_object_t object, vm_pindex_t start, vm_size_t size)
  705 {
  706         int s = splvm();
  707 
  708         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  709         swp_pager_meta_free(object, start, size);
  710         splx(s);
  711 }
  712 
  713 /*
  714  * SWAP_PAGER_RESERVE() - reserve swap blocks in object
  715  *
  716  *      Assigns swap blocks to the specified range within the object.  The 
  717  *      swap blocks are not zerod.  Any previous swap assignment is destroyed.
  718  *
  719  *      Returns 0 on success, -1 on failure.
  720  */
  721 int
  722 swap_pager_reserve(vm_object_t object, vm_pindex_t start, vm_size_t size)
  723 {
  724         int s;
  725         int n = 0;
  726         daddr_t blk = SWAPBLK_NONE;
  727         vm_pindex_t beg = start;        /* save start index */
  728 
  729         s = splvm();
  730         VM_OBJECT_LOCK(object);
  731         while (size) {
  732                 if (n == 0) {
  733                         n = BLIST_MAX_ALLOC;
  734                         while ((blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE) {
  735                                 n >>= 1;
  736                                 if (n == 0) {
  737                                         swp_pager_meta_free(object, beg, start - beg);
  738                                         VM_OBJECT_UNLOCK(object);
  739                                         splx(s);
  740                                         return (-1);
  741                                 }
  742                         }
  743                 }
  744                 swp_pager_meta_build(object, start, blk);
  745                 --size;
  746                 ++start;
  747                 ++blk;
  748                 --n;
  749         }
  750         swp_pager_meta_free(object, start, n);
  751         VM_OBJECT_UNLOCK(object);
  752         splx(s);
  753         return (0);
  754 }
  755 
  756 /*
  757  * SWAP_PAGER_COPY() -  copy blocks from source pager to destination pager
  758  *                      and destroy the source.
  759  *
  760  *      Copy any valid swapblks from the source to the destination.  In
  761  *      cases where both the source and destination have a valid swapblk,
  762  *      we keep the destination's.
  763  *
  764  *      This routine is allowed to block.  It may block allocating metadata
  765  *      indirectly through swp_pager_meta_build() or if paging is still in
  766  *      progress on the source. 
  767  *
  768  *      This routine can be called at any spl
  769  *
  770  *      XXX vm_page_collapse() kinda expects us not to block because we 
  771  *      supposedly do not need to allocate memory, but for the moment we
  772  *      *may* have to get a little memory from the zone allocator, but
  773  *      it is taken from the interrupt memory.  We should be ok. 
  774  *
  775  *      The source object contains no vm_page_t's (which is just as well)
  776  *
  777  *      The source object is of type OBJT_SWAP.
  778  *
  779  *      The source and destination objects must be locked or 
  780  *      inaccessible (XXX are they ?)
  781  */
  782 void
  783 swap_pager_copy(vm_object_t srcobject, vm_object_t dstobject,
  784     vm_pindex_t offset, int destroysource)
  785 {
  786         vm_pindex_t i;
  787         int s;
  788 
  789         VM_OBJECT_LOCK_ASSERT(srcobject, MA_OWNED);
  790         VM_OBJECT_LOCK_ASSERT(dstobject, MA_OWNED);
  791 
  792         s = splvm();
  793         /*
  794          * If destroysource is set, we remove the source object from the 
  795          * swap_pager internal queue now. 
  796          */
  797         if (destroysource) {
  798                 mtx_lock(&sw_alloc_mtx);
  799                 if (srcobject->handle == NULL) {
  800                         TAILQ_REMOVE(
  801                             &swap_pager_un_object_list, 
  802                             srcobject, 
  803                             pager_object_list
  804                         );
  805                 } else {
  806                         TAILQ_REMOVE(
  807                             NOBJLIST(srcobject->handle),
  808                             srcobject,
  809                             pager_object_list
  810                         );
  811                 }
  812                 mtx_unlock(&sw_alloc_mtx);
  813         }
  814 
  815         /*
  816          * transfer source to destination.
  817          */
  818         for (i = 0; i < dstobject->size; ++i) {
  819                 daddr_t dstaddr;
  820 
  821                 /*
  822                  * Locate (without changing) the swapblk on the destination,
  823                  * unless it is invalid in which case free it silently, or
  824                  * if the destination is a resident page, in which case the
  825                  * source is thrown away.
  826                  */
  827                 dstaddr = swp_pager_meta_ctl(dstobject, i, 0);
  828 
  829                 if (dstaddr == SWAPBLK_NONE) {
  830                         /*
  831                          * Destination has no swapblk and is not resident,
  832                          * copy source.
  833                          */
  834                         daddr_t srcaddr;
  835 
  836                         srcaddr = swp_pager_meta_ctl(
  837                             srcobject, 
  838                             i + offset,
  839                             SWM_POP
  840                         );
  841 
  842                         if (srcaddr != SWAPBLK_NONE) {
  843                                 /*
  844                                  * swp_pager_meta_build() can sleep.
  845                                  */
  846                                 vm_object_pip_add(srcobject, 1);
  847                                 VM_OBJECT_UNLOCK(srcobject);
  848                                 vm_object_pip_add(dstobject, 1);
  849                                 swp_pager_meta_build(dstobject, i, srcaddr);
  850                                 vm_object_pip_wakeup(dstobject);
  851                                 VM_OBJECT_LOCK(srcobject);
  852                                 vm_object_pip_wakeup(srcobject);
  853                         }
  854                 } else {
  855                         /*
  856                          * Destination has valid swapblk or it is represented
  857                          * by a resident page.  We destroy the sourceblock.
  858                          */
  859                         
  860                         swp_pager_meta_ctl(srcobject, i + offset, SWM_FREE);
  861                 }
  862         }
  863 
  864         /*
  865          * Free left over swap blocks in source.
  866          *
  867          * We have to revert the type to OBJT_DEFAULT so we do not accidently
  868          * double-remove the object from the swap queues.
  869          */
  870         if (destroysource) {
  871                 swp_pager_meta_free_all(srcobject);
  872                 /*
  873                  * Reverting the type is not necessary, the caller is going
  874                  * to destroy srcobject directly, but I'm doing it here
  875                  * for consistency since we've removed the object from its
  876                  * queues.
  877                  */
  878                 srcobject->type = OBJT_DEFAULT;
  879         }
  880         splx(s);
  881 }
  882 
  883 /*
  884  * SWAP_PAGER_HASPAGE() -       determine if we have good backing store for
  885  *                              the requested page.
  886  *
  887  *      We determine whether good backing store exists for the requested
  888  *      page and return TRUE if it does, FALSE if it doesn't.
  889  *
  890  *      If TRUE, we also try to determine how much valid, contiguous backing
  891  *      store exists before and after the requested page within a reasonable
  892  *      distance.  We do not try to restrict it to the swap device stripe
  893  *      (that is handled in getpages/putpages).  It probably isn't worth
  894  *      doing here.
  895  */
  896 static boolean_t
  897 swap_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before, int *after)
  898 {
  899         daddr_t blk0;
  900         int s;
  901 
  902         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
  903         /*
  904          * do we have good backing store at the requested index ?
  905          */
  906         s = splvm();
  907         blk0 = swp_pager_meta_ctl(object, pindex, 0);
  908 
  909         if (blk0 == SWAPBLK_NONE) {
  910                 splx(s);
  911                 if (before)
  912                         *before = 0;
  913                 if (after)
  914                         *after = 0;
  915                 return (FALSE);
  916         }
  917 
  918         /*
  919          * find backwards-looking contiguous good backing store
  920          */
  921         if (before != NULL) {
  922                 int i;
  923 
  924                 for (i = 1; i < (SWB_NPAGES/2); ++i) {
  925                         daddr_t blk;
  926 
  927                         if (i > pindex)
  928                                 break;
  929                         blk = swp_pager_meta_ctl(object, pindex - i, 0);
  930                         if (blk != blk0 - i)
  931                                 break;
  932                 }
  933                 *before = (i - 1);
  934         }
  935 
  936         /*
  937          * find forward-looking contiguous good backing store
  938          */
  939         if (after != NULL) {
  940                 int i;
  941 
  942                 for (i = 1; i < (SWB_NPAGES/2); ++i) {
  943                         daddr_t blk;
  944 
  945                         blk = swp_pager_meta_ctl(object, pindex + i, 0);
  946                         if (blk != blk0 + i)
  947                                 break;
  948                 }
  949                 *after = (i - 1);
  950         }
  951         splx(s);
  952         return (TRUE);
  953 }
  954 
  955 /*
  956  * SWAP_PAGER_PAGE_UNSWAPPED() - remove swap backing store related to page
  957  *
  958  *      This removes any associated swap backing store, whether valid or
  959  *      not, from the page.  
  960  *
  961  *      This routine is typically called when a page is made dirty, at
  962  *      which point any associated swap can be freed.  MADV_FREE also
  963  *      calls us in a special-case situation
  964  *
  965  *      NOTE!!!  If the page is clean and the swap was valid, the caller
  966  *      should make the page dirty before calling this routine.  This routine
  967  *      does NOT change the m->dirty status of the page.  Also: MADV_FREE
  968  *      depends on it.
  969  *
  970  *      This routine may not block
  971  *      This routine must be called at splvm()
  972  */
  973 static void
  974 swap_pager_unswapped(vm_page_t m)
  975 {
  976 
  977         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
  978         swp_pager_meta_ctl(m->object, m->pindex, SWM_FREE);
  979 }
  980 
  981 /*
  982  * SWAP_PAGER_GETPAGES() - bring pages in from swap
  983  *
  984  *      Attempt to retrieve (m, count) pages from backing store, but make
  985  *      sure we retrieve at least m[reqpage].  We try to load in as large
  986  *      a chunk surrounding m[reqpage] as is contiguous in swap and which
  987  *      belongs to the same object.
  988  *
  989  *      The code is designed for asynchronous operation and 
  990  *      immediate-notification of 'reqpage' but tends not to be
  991  *      used that way.  Please do not optimize-out this algorithmic
  992  *      feature, I intend to improve on it in the future.
  993  *
  994  *      The parent has a single vm_object_pip_add() reference prior to
  995  *      calling us and we should return with the same.
  996  *
  997  *      The parent has BUSY'd the pages.  We should return with 'm'
  998  *      left busy, but the others adjusted.
  999  */
 1000 static int
 1001 swap_pager_getpages(vm_object_t object, vm_page_t *m, int count, int reqpage)
 1002 {
 1003         struct buf *bp;
 1004         vm_page_t mreq;
 1005         int s;
 1006         int i;
 1007         int j;
 1008         daddr_t blk;
 1009 
 1010         mreq = m[reqpage];
 1011 
 1012         KASSERT(mreq->object == object,
 1013             ("swap_pager_getpages: object mismatch %p/%p",
 1014             object, mreq->object));
 1015 
 1016         /*
 1017          * Calculate range to retrieve.  The pages have already been assigned
 1018          * their swapblks.  We require a *contiguous* range but we know it to
 1019          * not span devices.   If we do not supply it, bad things
 1020          * happen.  Note that blk, iblk & jblk can be SWAPBLK_NONE, but the 
 1021          * loops are set up such that the case(s) are handled implicitly.
 1022          *
 1023          * The swp_*() calls must be made at splvm().  vm_page_free() does
 1024          * not need to be, but it will go a little faster if it is.
 1025          */
 1026         s = splvm();
 1027         blk = swp_pager_meta_ctl(mreq->object, mreq->pindex, 0);
 1028 
 1029         for (i = reqpage - 1; i >= 0; --i) {
 1030                 daddr_t iblk;
 1031 
 1032                 iblk = swp_pager_meta_ctl(m[i]->object, m[i]->pindex, 0);
 1033                 if (blk != iblk + (reqpage - i))
 1034                         break;
 1035         }
 1036         ++i;
 1037 
 1038         for (j = reqpage + 1; j < count; ++j) {
 1039                 daddr_t jblk;
 1040 
 1041                 jblk = swp_pager_meta_ctl(m[j]->object, m[j]->pindex, 0);
 1042                 if (blk != jblk - (j - reqpage))
 1043                         break;
 1044         }
 1045 
 1046         /*
 1047          * free pages outside our collection range.   Note: we never free
 1048          * mreq, it must remain busy throughout.
 1049          */
 1050         vm_page_lock_queues();
 1051         {
 1052                 int k;
 1053 
 1054                 for (k = 0; k < i; ++k)
 1055                         vm_page_free(m[k]);
 1056                 for (k = j; k < count; ++k)
 1057                         vm_page_free(m[k]);
 1058         }
 1059         vm_page_unlock_queues();
 1060         splx(s);
 1061 
 1062 
 1063         /*
 1064          * Return VM_PAGER_FAIL if we have nothing to do.  Return mreq 
 1065          * still busy, but the others unbusied.
 1066          */
 1067         if (blk == SWAPBLK_NONE)
 1068                 return (VM_PAGER_FAIL);
 1069 
 1070         /*
 1071          * Getpbuf() can sleep.
 1072          */
 1073         VM_OBJECT_UNLOCK(object);
 1074         /*
 1075          * Get a swap buffer header to perform the IO
 1076          */
 1077         bp = getpbuf(&nsw_rcount);
 1078         bp->b_flags |= B_PAGING;
 1079 
 1080         /*
 1081          * map our page(s) into kva for input
 1082          */
 1083         pmap_qenter((vm_offset_t)bp->b_data, m + i, j - i);
 1084 
 1085         bp->b_iocmd = BIO_READ;
 1086         bp->b_iodone = swp_pager_async_iodone;
 1087         bp->b_rcred = crhold(thread0.td_ucred);
 1088         bp->b_wcred = crhold(thread0.td_ucred);
 1089         bp->b_blkno = blk - (reqpage - i);
 1090         bp->b_bcount = PAGE_SIZE * (j - i);
 1091         bp->b_bufsize = PAGE_SIZE * (j - i);
 1092         bp->b_pager.pg_reqpage = reqpage - i;
 1093 
 1094         VM_OBJECT_LOCK(object);
 1095         vm_page_lock_queues();
 1096         {
 1097                 int k;
 1098 
 1099                 for (k = i; k < j; ++k) {
 1100                         bp->b_pages[k - i] = m[k];
 1101                         vm_page_flag_set(m[k], PG_SWAPINPROG);
 1102                 }
 1103         }
 1104         vm_page_unlock_queues();
 1105         VM_OBJECT_UNLOCK(object);
 1106         bp->b_npages = j - i;
 1107 
 1108         cnt.v_swapin++;
 1109         cnt.v_swappgsin += bp->b_npages;
 1110 
 1111         /*
 1112          * We still hold the lock on mreq, and our automatic completion routine
 1113          * does not remove it.
 1114          */
 1115         VM_OBJECT_LOCK(mreq->object);
 1116         vm_object_pip_add(mreq->object, bp->b_npages);
 1117         VM_OBJECT_UNLOCK(mreq->object);
 1118 
 1119         /*
 1120          * perform the I/O.  NOTE!!!  bp cannot be considered valid after
 1121          * this point because we automatically release it on completion.
 1122          * Instead, we look at the one page we are interested in which we
 1123          * still hold a lock on even through the I/O completion.
 1124          *
 1125          * The other pages in our m[] array are also released on completion,
 1126          * so we cannot assume they are valid anymore either.
 1127          *
 1128          * NOTE: b_blkno is destroyed by the call to swapdev_strategy
 1129          */
 1130         BUF_KERNPROC(bp);
 1131         swp_pager_strategy(bp);
 1132 
 1133         /*
 1134          * wait for the page we want to complete.  PG_SWAPINPROG is always
 1135          * cleared on completion.  If an I/O error occurs, SWAPBLK_NONE
 1136          * is set in the meta-data.
 1137          */
 1138         s = splvm();
 1139         vm_page_lock_queues();
 1140         while ((mreq->flags & PG_SWAPINPROG) != 0) {
 1141                 vm_page_flag_set(mreq, PG_WANTED | PG_REFERENCED);
 1142                 cnt.v_intrans++;
 1143                 if (msleep(mreq, &vm_page_queue_mtx, PSWP, "swread", hz*20)) {
 1144                         printf(
 1145                             "swap_pager: indefinite wait buffer: device:"
 1146                                 " %s, blkno: %ld, size: %ld\n",
 1147                             devtoname(bp->b_dev), (long)bp->b_blkno,
 1148                             bp->b_bcount
 1149                         );
 1150                 }
 1151         }
 1152         vm_page_unlock_queues();
 1153         splx(s);
 1154 
 1155         VM_OBJECT_LOCK(mreq->object);
 1156         /*
 1157          * mreq is left busied after completion, but all the other pages
 1158          * are freed.  If we had an unrecoverable read error the page will
 1159          * not be valid.
 1160          */
 1161         if (mreq->valid != VM_PAGE_BITS_ALL) {
 1162                 return (VM_PAGER_ERROR);
 1163         } else {
 1164                 return (VM_PAGER_OK);
 1165         }
 1166 
 1167         /*
 1168          * A final note: in a low swap situation, we cannot deallocate swap
 1169          * and mark a page dirty here because the caller is likely to mark
 1170          * the page clean when we return, causing the page to possibly revert 
 1171          * to all-zero's later.
 1172          */
 1173 }
 1174 
 1175 /*
 1176  *      swap_pager_putpages: 
 1177  *
 1178  *      Assign swap (if necessary) and initiate I/O on the specified pages.
 1179  *
 1180  *      We support both OBJT_DEFAULT and OBJT_SWAP objects.  DEFAULT objects
 1181  *      are automatically converted to SWAP objects.
 1182  *
 1183  *      In a low memory situation we may block in VOP_STRATEGY(), but the new 
 1184  *      vm_page reservation system coupled with properly written VFS devices 
 1185  *      should ensure that no low-memory deadlock occurs.  This is an area
 1186  *      which needs work.
 1187  *
 1188  *      The parent has N vm_object_pip_add() references prior to
 1189  *      calling us and will remove references for rtvals[] that are
 1190  *      not set to VM_PAGER_PEND.  We need to remove the rest on I/O
 1191  *      completion.
 1192  *
 1193  *      The parent has soft-busy'd the pages it passes us and will unbusy
 1194  *      those whos rtvals[] entry is not set to VM_PAGER_PEND on return.
 1195  *      We need to unbusy the rest on I/O completion.
 1196  */
 1197 void
 1198 swap_pager_putpages(vm_object_t object, vm_page_t *m, int count,
 1199     boolean_t sync, int *rtvals)
 1200 {
 1201         int i;
 1202         int n = 0;
 1203 
 1204         GIANT_REQUIRED;
 1205         if (count && m[0]->object != object) {
 1206                 panic("swap_pager_getpages: object mismatch %p/%p", 
 1207                     object, 
 1208                     m[0]->object
 1209                 );
 1210         }
 1211 
 1212         /*
 1213          * Step 1
 1214          *
 1215          * Turn object into OBJT_SWAP
 1216          * check for bogus sysops
 1217          * force sync if not pageout process
 1218          */
 1219         if (object->type != OBJT_SWAP)
 1220                 swp_pager_meta_build(object, 0, SWAPBLK_NONE);
 1221         VM_OBJECT_UNLOCK(object);
 1222 
 1223         if (curproc != pageproc)
 1224                 sync = TRUE;
 1225 
 1226         /*
 1227          * Step 2
 1228          *
 1229          * Update nsw parameters from swap_async_max sysctl values.  
 1230          * Do not let the sysop crash the machine with bogus numbers.
 1231          */
 1232         mtx_lock(&pbuf_mtx);
 1233         if (swap_async_max != nsw_wcount_async_max) {
 1234                 int n;
 1235                 int s;
 1236 
 1237                 /*
 1238                  * limit range
 1239                  */
 1240                 if ((n = swap_async_max) > nswbuf / 2)
 1241                         n = nswbuf / 2;
 1242                 if (n < 1)
 1243                         n = 1;
 1244                 swap_async_max = n;
 1245 
 1246                 /*
 1247                  * Adjust difference ( if possible ).  If the current async
 1248                  * count is too low, we may not be able to make the adjustment
 1249                  * at this time.
 1250                  */
 1251                 s = splvm();
 1252                 n -= nsw_wcount_async_max;
 1253                 if (nsw_wcount_async + n >= 0) {
 1254                         nsw_wcount_async += n;
 1255                         nsw_wcount_async_max += n;
 1256                         wakeup(&nsw_wcount_async);
 1257                 }
 1258                 splx(s);
 1259         }
 1260         mtx_unlock(&pbuf_mtx);
 1261 
 1262         /*
 1263          * Step 3
 1264          *
 1265          * Assign swap blocks and issue I/O.  We reallocate swap on the fly.
 1266          * The page is left dirty until the pageout operation completes
 1267          * successfully.
 1268          */
 1269         for (i = 0; i < count; i += n) {
 1270                 int s;
 1271                 int j;
 1272                 struct buf *bp;
 1273                 daddr_t blk;
 1274 
 1275                 /*
 1276                  * Maximum I/O size is limited by a number of factors.
 1277                  */
 1278                 n = min(BLIST_MAX_ALLOC, count - i);
 1279                 n = min(n, nsw_cluster_max);
 1280 
 1281                 s = splvm();
 1282 
 1283                 /*
 1284                  * Get biggest block of swap we can.  If we fail, fall
 1285                  * back and try to allocate a smaller block.  Don't go
 1286                  * overboard trying to allocate space if it would overly
 1287                  * fragment swap.
 1288                  */
 1289                 while (
 1290                     (blk = swp_pager_getswapspace(n)) == SWAPBLK_NONE &&
 1291                     n > 4
 1292                 ) {
 1293                         n >>= 1;
 1294                 }
 1295                 if (blk == SWAPBLK_NONE) {
 1296                         for (j = 0; j < n; ++j)
 1297                                 rtvals[i+j] = VM_PAGER_FAIL;
 1298                         splx(s);
 1299                         continue;
 1300                 }
 1301 
 1302                 /*
 1303                  * All I/O parameters have been satisfied, build the I/O
 1304                  * request and assign the swap space.
 1305                  */
 1306                 if (sync == TRUE) {
 1307                         bp = getpbuf(&nsw_wcount_sync);
 1308                 } else {
 1309                         bp = getpbuf(&nsw_wcount_async);
 1310                         bp->b_flags = B_ASYNC;
 1311                 }
 1312                 bp->b_flags |= B_PAGING;
 1313                 bp->b_iocmd = BIO_WRITE;
 1314 
 1315                 pmap_qenter((vm_offset_t)bp->b_data, &m[i], n);
 1316 
 1317                 bp->b_rcred = crhold(thread0.td_ucred);
 1318                 bp->b_wcred = crhold(thread0.td_ucred);
 1319                 bp->b_bcount = PAGE_SIZE * n;
 1320                 bp->b_bufsize = PAGE_SIZE * n;
 1321                 bp->b_blkno = blk;
 1322 
 1323                 VM_OBJECT_LOCK(object);
 1324                 for (j = 0; j < n; ++j) {
 1325                         vm_page_t mreq = m[i+j];
 1326 
 1327                         swp_pager_meta_build(
 1328                             mreq->object, 
 1329                             mreq->pindex,
 1330                             blk + j
 1331                         );
 1332                         vm_page_dirty(mreq);
 1333                         rtvals[i+j] = VM_PAGER_OK;
 1334 
 1335                         vm_page_lock_queues();
 1336                         vm_page_flag_set(mreq, PG_SWAPINPROG);
 1337                         vm_page_unlock_queues();
 1338                         bp->b_pages[j] = mreq;
 1339                 }
 1340                 VM_OBJECT_UNLOCK(object);
 1341                 bp->b_npages = n;
 1342                 /*
 1343                  * Must set dirty range for NFS to work.
 1344                  */
 1345                 bp->b_dirtyoff = 0;
 1346                 bp->b_dirtyend = bp->b_bcount;
 1347 
 1348                 cnt.v_swapout++;
 1349                 cnt.v_swappgsout += bp->b_npages;
 1350 
 1351                 splx(s);
 1352 
 1353                 /*
 1354                  * asynchronous
 1355                  *
 1356                  * NOTE: b_blkno is destroyed by the call to swapdev_strategy
 1357                  */
 1358                 if (sync == FALSE) {
 1359                         bp->b_iodone = swp_pager_async_iodone;
 1360                         BUF_KERNPROC(bp);
 1361                         swp_pager_strategy(bp);
 1362 
 1363                         for (j = 0; j < n; ++j)
 1364                                 rtvals[i+j] = VM_PAGER_PEND;
 1365                         /* restart outter loop */
 1366                         continue;
 1367                 }
 1368 
 1369                 /*
 1370                  * synchronous
 1371                  *
 1372                  * NOTE: b_blkno is destroyed by the call to swapdev_strategy
 1373                  */
 1374                 bp->b_iodone = swp_pager_sync_iodone;
 1375                 swp_pager_strategy(bp);
 1376 
 1377                 /*
 1378                  * Wait for the sync I/O to complete, then update rtvals.
 1379                  * We just set the rtvals[] to VM_PAGER_PEND so we can call
 1380                  * our async completion routine at the end, thus avoiding a
 1381                  * double-free.
 1382                  */
 1383                 s = splbio();
 1384                 while ((bp->b_flags & B_DONE) == 0) {
 1385                         tsleep(bp, PVM, "swwrt", 0);
 1386                 }
 1387                 for (j = 0; j < n; ++j)
 1388                         rtvals[i+j] = VM_PAGER_PEND;
 1389                 /*
 1390                  * Now that we are through with the bp, we can call the
 1391                  * normal async completion, which frees everything up.
 1392                  */
 1393                 swp_pager_async_iodone(bp);
 1394                 splx(s);
 1395         }
 1396         VM_OBJECT_LOCK(object);
 1397 }
 1398 
 1399 /*
 1400  *      swap_pager_sync_iodone:
 1401  *
 1402  *      Completion routine for synchronous reads and writes from/to swap.
 1403  *      We just mark the bp is complete and wake up anyone waiting on it.
 1404  *
 1405  *      This routine may not block.  This routine is called at splbio() or better.
 1406  */
 1407 static void
 1408 swp_pager_sync_iodone(struct buf *bp)
 1409 {
 1410         bp->b_flags |= B_DONE;
 1411         bp->b_flags &= ~B_ASYNC;
 1412         wakeup(bp);
 1413 }
 1414 
 1415 /*
 1416  *      swp_pager_async_iodone:
 1417  *
 1418  *      Completion routine for asynchronous reads and writes from/to swap.
 1419  *      Also called manually by synchronous code to finish up a bp.
 1420  *
 1421  *      For READ operations, the pages are PG_BUSY'd.  For WRITE operations, 
 1422  *      the pages are vm_page_t->busy'd.  For READ operations, we PG_BUSY 
 1423  *      unbusy all pages except the 'main' request page.  For WRITE 
 1424  *      operations, we vm_page_t->busy'd unbusy all pages ( we can do this 
 1425  *      because we marked them all VM_PAGER_PEND on return from putpages ).
 1426  *
 1427  *      This routine may not block.
 1428  *      This routine is called at splbio() or better
 1429  *
 1430  *      We up ourselves to splvm() as required for various vm_page related
 1431  *      calls.
 1432  */
 1433 static void
 1434 swp_pager_async_iodone(struct buf *bp)
 1435 {
 1436         int s;
 1437         int i;
 1438         vm_object_t object = NULL;
 1439 
 1440         GIANT_REQUIRED;
 1441         bp->b_flags |= B_DONE;
 1442 
 1443         /*
 1444          * report error
 1445          */
 1446         if (bp->b_ioflags & BIO_ERROR) {
 1447                 printf(
 1448                     "swap_pager: I/O error - %s failed; blkno %ld,"
 1449                         "size %ld, error %d\n",
 1450                     ((bp->b_iocmd == BIO_READ) ? "pagein" : "pageout"),
 1451                     (long)bp->b_blkno, 
 1452                     (long)bp->b_bcount,
 1453                     bp->b_error
 1454                 );
 1455         }
 1456 
 1457         /*
 1458          * set object, raise to splvm().
 1459          */
 1460         s = splvm();
 1461 
 1462         /*
 1463          * remove the mapping for kernel virtual
 1464          */
 1465         pmap_qremove((vm_offset_t)bp->b_data, bp->b_npages);
 1466 
 1467         if (bp->b_npages) {
 1468                 object = bp->b_pages[0]->object;
 1469                 VM_OBJECT_LOCK(object);
 1470         }
 1471         vm_page_lock_queues();
 1472         /*
 1473          * cleanup pages.  If an error occurs writing to swap, we are in
 1474          * very serious trouble.  If it happens to be a disk error, though,
 1475          * we may be able to recover by reassigning the swap later on.  So
 1476          * in this case we remove the m->swapblk assignment for the page 
 1477          * but do not free it in the rlist.  The errornous block(s) are thus
 1478          * never reallocated as swap.  Redirty the page and continue.
 1479          */
 1480         for (i = 0; i < bp->b_npages; ++i) {
 1481                 vm_page_t m = bp->b_pages[i];
 1482 
 1483                 vm_page_flag_clear(m, PG_SWAPINPROG);
 1484 
 1485                 if (bp->b_ioflags & BIO_ERROR) {
 1486                         /*
 1487                          * If an error occurs I'd love to throw the swapblk
 1488                          * away without freeing it back to swapspace, so it
 1489                          * can never be used again.  But I can't from an 
 1490                          * interrupt.
 1491                          */
 1492                         if (bp->b_iocmd == BIO_READ) {
 1493                                 /*
 1494                                  * When reading, reqpage needs to stay
 1495                                  * locked for the parent, but all other
 1496                                  * pages can be freed.  We still want to
 1497                                  * wakeup the parent waiting on the page,
 1498                                  * though.  ( also: pg_reqpage can be -1 and 
 1499                                  * not match anything ).
 1500                                  *
 1501                                  * We have to wake specifically requested pages
 1502                                  * up too because we cleared PG_SWAPINPROG and
 1503                                  * someone may be waiting for that.
 1504                                  *
 1505                                  * NOTE: for reads, m->dirty will probably
 1506                                  * be overridden by the original caller of
 1507                                  * getpages so don't play cute tricks here.
 1508                                  *
 1509                                  * XXX IT IS NOT LEGAL TO FREE THE PAGE HERE
 1510                                  * AS THIS MESSES WITH object->memq, and it is
 1511                                  * not legal to mess with object->memq from an
 1512                                  * interrupt.
 1513                                  */
 1514                                 m->valid = 0;
 1515                                 vm_page_flag_clear(m, PG_ZERO);
 1516                                 if (i != bp->b_pager.pg_reqpage)
 1517                                         vm_page_free(m);
 1518                                 else
 1519                                         vm_page_flash(m);
 1520                                 /*
 1521                                  * If i == bp->b_pager.pg_reqpage, do not wake 
 1522                                  * the page up.  The caller needs to.
 1523                                  */
 1524                         } else {
 1525                                 /*
 1526                                  * If a write error occurs, reactivate page
 1527                                  * so it doesn't clog the inactive list,
 1528                                  * then finish the I/O.
 1529                                  */
 1530                                 vm_page_dirty(m);
 1531                                 vm_page_activate(m);
 1532                                 vm_page_io_finish(m);
 1533                         }
 1534                 } else if (bp->b_iocmd == BIO_READ) {
 1535                         /*
 1536                          * For read success, clear dirty bits.  Nobody should
 1537                          * have this page mapped but don't take any chances,
 1538                          * make sure the pmap modify bits are also cleared.
 1539                          *
 1540                          * NOTE: for reads, m->dirty will probably be 
 1541                          * overridden by the original caller of getpages so
 1542                          * we cannot set them in order to free the underlying
 1543                          * swap in a low-swap situation.  I don't think we'd
 1544                          * want to do that anyway, but it was an optimization
 1545                          * that existed in the old swapper for a time before
 1546                          * it got ripped out due to precisely this problem.
 1547                          *
 1548                          * clear PG_ZERO in page.
 1549                          *
 1550                          * If not the requested page then deactivate it.
 1551                          *
 1552                          * Note that the requested page, reqpage, is left
 1553                          * busied, but we still have to wake it up.  The
 1554                          * other pages are released (unbusied) by 
 1555                          * vm_page_wakeup().  We do not set reqpage's
 1556                          * valid bits here, it is up to the caller.
 1557                          */
 1558                         pmap_clear_modify(m);
 1559                         m->valid = VM_PAGE_BITS_ALL;
 1560                         vm_page_undirty(m);
 1561                         vm_page_flag_clear(m, PG_ZERO);
 1562 
 1563                         /*
 1564                          * We have to wake specifically requested pages
 1565                          * up too because we cleared PG_SWAPINPROG and
 1566                          * could be waiting for it in getpages.  However,
 1567                          * be sure to not unbusy getpages specifically
 1568                          * requested page - getpages expects it to be 
 1569                          * left busy.
 1570                          */
 1571                         if (i != bp->b_pager.pg_reqpage) {
 1572                                 vm_page_deactivate(m);
 1573                                 vm_page_wakeup(m);
 1574                         } else {
 1575                                 vm_page_flash(m);
 1576                         }
 1577                 } else {
 1578                         /*
 1579                          * For write success, clear the modify and dirty 
 1580                          * status, then finish the I/O ( which decrements the 
 1581                          * busy count and possibly wakes waiter's up ).
 1582                          */
 1583                         pmap_clear_modify(m);
 1584                         vm_page_undirty(m);
 1585                         vm_page_io_finish(m);
 1586                         if (!vm_page_count_severe() || !vm_page_try_to_cache(m))
 1587                                 pmap_page_protect(m, VM_PROT_READ);
 1588                 }
 1589         }
 1590         vm_page_unlock_queues();
 1591 
 1592         /*
 1593          * adjust pip.  NOTE: the original parent may still have its own
 1594          * pip refs on the object.
 1595          */
 1596         if (object != NULL) {
 1597                 vm_object_pip_wakeupn(object, bp->b_npages);
 1598                 VM_OBJECT_UNLOCK(object);
 1599         }
 1600 
 1601         /*
 1602          * release the physical I/O buffer
 1603          */
 1604         relpbuf(
 1605             bp, 
 1606             ((bp->b_iocmd == BIO_READ) ? &nsw_rcount : 
 1607                 ((bp->b_flags & B_ASYNC) ? 
 1608                     &nsw_wcount_async : 
 1609                     &nsw_wcount_sync
 1610                 )
 1611             )
 1612         );
 1613         splx(s);
 1614 }
 1615 
 1616 /*
 1617  *      swap_pager_isswapped:
 1618  *
 1619  *      Return 1 if at least one page in the given object is paged
 1620  *      out to the given swap device.
 1621  *
 1622  *      This routine may not block.
 1623  */
 1624 int
 1625 swap_pager_isswapped(vm_object_t object, struct swdevt *sp)
 1626 {
 1627         daddr_t index = 0;
 1628         int bcount;
 1629         int i;
 1630 
 1631         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 1632         for (bcount = 0; bcount < object->un_pager.swp.swp_bcount; bcount++) {
 1633                 struct swblock *swap;
 1634 
 1635                 mtx_lock(&swhash_mtx);
 1636                 if ((swap = *swp_pager_hash(object, index)) != NULL) {
 1637                         for (i = 0; i < SWAP_META_PAGES; ++i) {
 1638                                 daddr_t v = swap->swb_pages[i];
 1639                                 if (v == SWAPBLK_NONE)
 1640                                         continue;
 1641                                 if (swp_pager_find_dev(v) == sp) {
 1642                                         mtx_unlock(&swhash_mtx);
 1643                                         return 1;
 1644                                 }
 1645                         }
 1646                 }
 1647                 mtx_unlock(&swhash_mtx);
 1648                 index += SWAP_META_PAGES;
 1649                 if (index > 0x20000000)
 1650                         panic("swap_pager_isswapped: failed to locate all swap meta blocks");
 1651         }
 1652         return 0;
 1653 }
 1654 
 1655 /*
 1656  * SWP_PAGER_FORCE_PAGEIN() - force a swap block to be paged in
 1657  *
 1658  *      This routine dissociates the page at the given index within a
 1659  *      swap block from its backing store, paging it in if necessary.
 1660  *      If the page is paged in, it is placed in the inactive queue,
 1661  *      since it had its backing store ripped out from under it.
 1662  *      We also attempt to swap in all other pages in the swap block,
 1663  *      we only guarantee that the one at the specified index is
 1664  *      paged in.
 1665  *
 1666  *      XXX - The code to page the whole block in doesn't work, so we
 1667  *            revert to the one-by-one behavior for now.  Sigh.
 1668  */
 1669 static __inline void
 1670 swp_pager_force_pagein(struct swblock *swap, int idx)
 1671 {
 1672         vm_object_t object;
 1673         vm_page_t m;
 1674         vm_pindex_t pindex;
 1675 
 1676         object = swap->swb_object;
 1677         pindex = swap->swb_index;
 1678         mtx_unlock(&swhash_mtx);
 1679 
 1680         VM_OBJECT_LOCK(object);
 1681         vm_object_pip_add(object, 1);
 1682         m = vm_page_grab(object, pindex + idx, VM_ALLOC_NORMAL|VM_ALLOC_RETRY);
 1683         if (m->valid == VM_PAGE_BITS_ALL) {
 1684                 vm_object_pip_subtract(object, 1);
 1685                 vm_page_lock_queues();
 1686                 vm_page_activate(m);
 1687                 vm_page_dirty(m);
 1688                 vm_page_wakeup(m);
 1689                 vm_page_unlock_queues();
 1690                 vm_pager_page_unswapped(m);
 1691                 VM_OBJECT_UNLOCK(object);
 1692                 return;
 1693         }
 1694 
 1695         if (swap_pager_getpages(object, &m, 1, 0) !=
 1696             VM_PAGER_OK)
 1697                 panic("swap_pager_force_pagein: read from swap failed");/*XXX*/
 1698         vm_object_pip_subtract(object, 1);
 1699         vm_page_lock_queues();
 1700         vm_page_dirty(m);
 1701         vm_page_dontneed(m);
 1702         vm_page_wakeup(m);
 1703         vm_page_unlock_queues();
 1704         vm_pager_page_unswapped(m);
 1705         VM_OBJECT_UNLOCK(object);
 1706 }
 1707 
 1708 
 1709 /*
 1710  *      swap_pager_swapoff:
 1711  *
 1712  *      Page in all of the pages that have been paged out to the
 1713  *      given device.  The corresponding blocks in the bitmap must be
 1714  *      marked as allocated and the device must be flagged SW_CLOSING.
 1715  *      There may be no processes swapped out to the device.
 1716  *
 1717  *      The sw_used parameter points to the field in the swdev structure
 1718  *      that contains a count of the number of blocks still allocated
 1719  *      on the device.  If we encounter objects with a nonzero pip count
 1720  *      in our scan, we use this number to determine if we're really done.
 1721  *
 1722  *      This routine may block.
 1723  */
 1724 static void
 1725 swap_pager_swapoff(struct swdevt *sp, int *sw_used)
 1726 {
 1727         struct swblock **pswap;
 1728         struct swblock *swap;
 1729         vm_object_t waitobj;
 1730         daddr_t v;
 1731         int i, j;
 1732 
 1733         GIANT_REQUIRED;
 1734 
 1735 full_rescan:
 1736         waitobj = NULL;
 1737         for (i = 0; i <= swhash_mask; i++) { /* '<=' is correct here */
 1738 restart:
 1739                 pswap = &swhash[i];
 1740                 mtx_lock(&swhash_mtx);
 1741                 while ((swap = *pswap) != NULL) {
 1742                         for (j = 0; j < SWAP_META_PAGES; ++j) {
 1743                                 v = swap->swb_pages[j];
 1744                                 if (v != SWAPBLK_NONE &&
 1745                                     swp_pager_find_dev(v) == sp)
 1746                                         break;
 1747                         }
 1748                         if (j < SWAP_META_PAGES) {
 1749                                 swp_pager_force_pagein(swap, j);
 1750                                 goto restart;
 1751                         } else if (swap->swb_object->paging_in_progress) {
 1752                                 if (!waitobj)
 1753                                         waitobj = swap->swb_object;
 1754                         }
 1755                         pswap = &swap->swb_hnext;
 1756                 }
 1757                 mtx_unlock(&swhash_mtx);
 1758         }
 1759         if (waitobj && *sw_used) {
 1760             /*
 1761              * We wait on an arbitrary object to clock our rescans
 1762              * to the rate of paging completion.
 1763              */
 1764             VM_OBJECT_LOCK(waitobj);
 1765             vm_object_pip_wait(waitobj, "swpoff");
 1766             VM_OBJECT_UNLOCK(waitobj);
 1767             goto full_rescan;
 1768         }
 1769         if (*sw_used)
 1770             panic("swapoff: failed to locate %d swap blocks", *sw_used);
 1771 }
 1772 
 1773 /************************************************************************
 1774  *                              SWAP META DATA                          *
 1775  ************************************************************************
 1776  *
 1777  *      These routines manipulate the swap metadata stored in the 
 1778  *      OBJT_SWAP object.  All swp_*() routines must be called at
 1779  *      splvm() because swap can be freed up by the low level vm_page
 1780  *      code which might be called from interrupts beyond what splbio() covers.
 1781  *
 1782  *      Swap metadata is implemented with a global hash and not directly
 1783  *      linked into the object.  Instead the object simply contains
 1784  *      appropriate tracking counters.
 1785  */
 1786 
 1787 /*
 1788  * SWP_PAGER_META_BUILD() -     add swap block to swap meta data for object
 1789  *
 1790  *      We first convert the object to a swap object if it is a default
 1791  *      object.
 1792  *
 1793  *      The specified swapblk is added to the object's swap metadata.  If
 1794  *      the swapblk is not valid, it is freed instead.  Any previously
 1795  *      assigned swapblk is freed.
 1796  *
 1797  *      This routine must be called at splvm(), except when used to convert
 1798  *      an OBJT_DEFAULT object into an OBJT_SWAP object.
 1799  */
 1800 static void
 1801 swp_pager_meta_build(vm_object_t object, vm_pindex_t pindex, daddr_t swapblk)
 1802 {
 1803         struct swblock *swap;
 1804         struct swblock **pswap;
 1805         int idx;
 1806 
 1807         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 1808         /*
 1809          * Convert default object to swap object if necessary
 1810          */
 1811         if (object->type != OBJT_SWAP) {
 1812                 object->type = OBJT_SWAP;
 1813                 object->un_pager.swp.swp_bcount = 0;
 1814 
 1815                 mtx_lock(&sw_alloc_mtx);
 1816                 if (object->handle != NULL) {
 1817                         TAILQ_INSERT_TAIL(
 1818                             NOBJLIST(object->handle),
 1819                             object, 
 1820                             pager_object_list
 1821                         );
 1822                 } else {
 1823                         TAILQ_INSERT_TAIL(
 1824                             &swap_pager_un_object_list,
 1825                             object, 
 1826                             pager_object_list
 1827                         );
 1828                 }
 1829                 mtx_unlock(&sw_alloc_mtx);
 1830         }
 1831         
 1832         /*
 1833          * Locate hash entry.  If not found create, but if we aren't adding
 1834          * anything just return.  If we run out of space in the map we wait
 1835          * and, since the hash table may have changed, retry.
 1836          */
 1837 retry:
 1838         mtx_lock(&swhash_mtx);
 1839         pswap = swp_pager_hash(object, pindex);
 1840 
 1841         if ((swap = *pswap) == NULL) {
 1842                 int i;
 1843 
 1844                 if (swapblk == SWAPBLK_NONE)
 1845                         goto done;
 1846 
 1847                 swap = *pswap = uma_zalloc(swap_zone, M_NOWAIT);
 1848                 if (swap == NULL) {
 1849                         mtx_unlock(&swhash_mtx);
 1850                         VM_OBJECT_UNLOCK(object);
 1851                         VM_WAIT;
 1852                         VM_OBJECT_LOCK(object);
 1853                         goto retry;
 1854                 }
 1855 
 1856                 swap->swb_hnext = NULL;
 1857                 swap->swb_object = object;
 1858                 swap->swb_index = pindex & ~(vm_pindex_t)SWAP_META_MASK;
 1859                 swap->swb_count = 0;
 1860 
 1861                 ++object->un_pager.swp.swp_bcount;
 1862 
 1863                 for (i = 0; i < SWAP_META_PAGES; ++i)
 1864                         swap->swb_pages[i] = SWAPBLK_NONE;
 1865         }
 1866 
 1867         /*
 1868          * Delete prior contents of metadata
 1869          */
 1870         idx = pindex & SWAP_META_MASK;
 1871 
 1872         if (swap->swb_pages[idx] != SWAPBLK_NONE) {
 1873                 swp_pager_freeswapspace(swap->swb_pages[idx], 1);
 1874                 --swap->swb_count;
 1875         }
 1876 
 1877         /*
 1878          * Enter block into metadata
 1879          */
 1880         swap->swb_pages[idx] = swapblk;
 1881         if (swapblk != SWAPBLK_NONE)
 1882                 ++swap->swb_count;
 1883 done:
 1884         mtx_unlock(&swhash_mtx);
 1885 }
 1886 
 1887 /*
 1888  * SWP_PAGER_META_FREE() - free a range of blocks in the object's swap metadata
 1889  *
 1890  *      The requested range of blocks is freed, with any associated swap 
 1891  *      returned to the swap bitmap.
 1892  *
 1893  *      This routine will free swap metadata structures as they are cleaned 
 1894  *      out.  This routine does *NOT* operate on swap metadata associated
 1895  *      with resident pages.
 1896  *
 1897  *      This routine must be called at splvm()
 1898  */
 1899 static void
 1900 swp_pager_meta_free(vm_object_t object, vm_pindex_t index, daddr_t count)
 1901 {
 1902 
 1903         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 1904         if (object->type != OBJT_SWAP)
 1905                 return;
 1906 
 1907         while (count > 0) {
 1908                 struct swblock **pswap;
 1909                 struct swblock *swap;
 1910 
 1911                 mtx_lock(&swhash_mtx);
 1912                 pswap = swp_pager_hash(object, index);
 1913 
 1914                 if ((swap = *pswap) != NULL) {
 1915                         daddr_t v = swap->swb_pages[index & SWAP_META_MASK];
 1916 
 1917                         if (v != SWAPBLK_NONE) {
 1918                                 swp_pager_freeswapspace(v, 1);
 1919                                 swap->swb_pages[index & SWAP_META_MASK] =
 1920                                         SWAPBLK_NONE;
 1921                                 if (--swap->swb_count == 0) {
 1922                                         *pswap = swap->swb_hnext;
 1923                                         uma_zfree(swap_zone, swap);
 1924                                         --object->un_pager.swp.swp_bcount;
 1925                                 }
 1926                         }
 1927                         --count;
 1928                         ++index;
 1929                 } else {
 1930                         int n = SWAP_META_PAGES - (index & SWAP_META_MASK);
 1931                         count -= n;
 1932                         index += n;
 1933                 }
 1934                 mtx_unlock(&swhash_mtx);
 1935         }
 1936 }
 1937 
 1938 /*
 1939  * SWP_PAGER_META_FREE_ALL() - destroy all swap metadata associated with object
 1940  *
 1941  *      This routine locates and destroys all swap metadata associated with
 1942  *      an object.
 1943  *
 1944  *      This routine must be called at splvm()
 1945  */
 1946 static void
 1947 swp_pager_meta_free_all(vm_object_t object)
 1948 {
 1949         daddr_t index = 0;
 1950 
 1951         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 1952         if (object->type != OBJT_SWAP)
 1953                 return;
 1954 
 1955         while (object->un_pager.swp.swp_bcount) {
 1956                 struct swblock **pswap;
 1957                 struct swblock *swap;
 1958 
 1959                 mtx_lock(&swhash_mtx);
 1960                 pswap = swp_pager_hash(object, index);
 1961                 if ((swap = *pswap) != NULL) {
 1962                         int i;
 1963 
 1964                         for (i = 0; i < SWAP_META_PAGES; ++i) {
 1965                                 daddr_t v = swap->swb_pages[i];
 1966                                 if (v != SWAPBLK_NONE) {
 1967                                         --swap->swb_count;
 1968                                         swp_pager_freeswapspace(v, 1);
 1969                                 }
 1970                         }
 1971                         if (swap->swb_count != 0)
 1972                                 panic("swap_pager_meta_free_all: swb_count != 0");
 1973                         *pswap = swap->swb_hnext;
 1974                         uma_zfree(swap_zone, swap);
 1975                         --object->un_pager.swp.swp_bcount;
 1976                 }
 1977                 mtx_unlock(&swhash_mtx);
 1978                 index += SWAP_META_PAGES;
 1979                 if (index > 0x20000000)
 1980                         panic("swp_pager_meta_free_all: failed to locate all swap meta blocks");
 1981         }
 1982 }
 1983 
 1984 /*
 1985  * SWP_PAGER_METACTL() -  misc control of swap and vm_page_t meta data.
 1986  *
 1987  *      This routine is capable of looking up, popping, or freeing
 1988  *      swapblk assignments in the swap meta data or in the vm_page_t.
 1989  *      The routine typically returns the swapblk being looked-up, or popped,
 1990  *      or SWAPBLK_NONE if the block was freed, or SWAPBLK_NONE if the block
 1991  *      was invalid.  This routine will automatically free any invalid 
 1992  *      meta-data swapblks.
 1993  *
 1994  *      It is not possible to store invalid swapblks in the swap meta data
 1995  *      (other then a literal 'SWAPBLK_NONE'), so we don't bother checking.
 1996  *
 1997  *      When acting on a busy resident page and paging is in progress, we 
 1998  *      have to wait until paging is complete but otherwise can act on the 
 1999  *      busy page.
 2000  *
 2001  *      This routine must be called at splvm().
 2002  *
 2003  *      SWM_FREE        remove and free swap block from metadata
 2004  *      SWM_POP         remove from meta data but do not free.. pop it out
 2005  */
 2006 static daddr_t
 2007 swp_pager_meta_ctl(vm_object_t object, vm_pindex_t pindex, int flags)
 2008 {
 2009         struct swblock **pswap;
 2010         struct swblock *swap;
 2011         daddr_t r1;
 2012         int idx;
 2013 
 2014         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 2015         /*
 2016          * The meta data only exists of the object is OBJT_SWAP 
 2017          * and even then might not be allocated yet.
 2018          */
 2019         if (object->type != OBJT_SWAP)
 2020                 return (SWAPBLK_NONE);
 2021 
 2022         r1 = SWAPBLK_NONE;
 2023         mtx_lock(&swhash_mtx);
 2024         pswap = swp_pager_hash(object, pindex);
 2025 
 2026         if ((swap = *pswap) != NULL) {
 2027                 idx = pindex & SWAP_META_MASK;
 2028                 r1 = swap->swb_pages[idx];
 2029 
 2030                 if (r1 != SWAPBLK_NONE) {
 2031                         if (flags & SWM_FREE) {
 2032                                 swp_pager_freeswapspace(r1, 1);
 2033                                 r1 = SWAPBLK_NONE;
 2034                         }
 2035                         if (flags & (SWM_FREE|SWM_POP)) {
 2036                                 swap->swb_pages[idx] = SWAPBLK_NONE;
 2037                                 if (--swap->swb_count == 0) {
 2038                                         *pswap = swap->swb_hnext;
 2039                                         uma_zfree(swap_zone, swap);
 2040                                         --object->un_pager.swp.swp_bcount;
 2041                                 }
 2042                         } 
 2043                 }
 2044         }
 2045         mtx_unlock(&swhash_mtx);
 2046         return (r1);
 2047 }
 2048 
 2049 /*
 2050  * System call swapon(name) enables swapping on device name,
 2051  * which must be in the swdevsw.  Return EBUSY
 2052  * if already swapping on this device.
 2053  */
 2054 #ifndef _SYS_SYSPROTO_H_
 2055 struct swapon_args {
 2056         char *name;
 2057 };
 2058 #endif
 2059 
 2060 /* 
 2061  * MPSAFE
 2062  */
 2063 /* ARGSUSED */
 2064 int
 2065 swapon(struct thread *td, struct swapon_args *uap)
 2066 {
 2067         struct vattr attr;
 2068         struct vnode *vp;
 2069         struct nameidata nd;
 2070         int error;
 2071 
 2072         mtx_lock(&Giant);
 2073         error = suser(td);
 2074         if (error)
 2075                 goto done2;
 2076 
 2077         while (swdev_syscall_active)
 2078             tsleep(&swdev_syscall_active, PUSER - 1, "swpon", 0);
 2079         swdev_syscall_active = 1;
 2080 
 2081         /*
 2082          * Swap metadata may not fit in the KVM if we have physical
 2083          * memory of >1GB.
 2084          */
 2085         if (swap_zone == NULL) {
 2086                 error = ENOMEM;
 2087                 goto done;
 2088         }
 2089 
 2090         NDINIT(&nd, LOOKUP, FOLLOW, UIO_USERSPACE, uap->name, td);
 2091         error = namei(&nd);
 2092         if (error)
 2093                 goto done;
 2094 
 2095         NDFREE(&nd, NDF_ONLY_PNBUF);
 2096         vp = nd.ni_vp;
 2097 
 2098         if (vn_isdisk(vp, &error)) {
 2099                 error = swapongeom(td, vp);
 2100         } else if (vp->v_type == VREG &&
 2101             (vp->v_mount->mnt_vfc->vfc_flags & VFCF_NETWORK) != 0 &&
 2102             (error = VOP_GETATTR(vp, &attr, td->td_ucred, td)) == 0) {
 2103                 /*
 2104                  * Allow direct swapping to NFS regular files in the same
 2105                  * way that nfs_mountroot() sets up diskless swapping.
 2106                  */
 2107                 error = swaponvp(td, vp, attr.va_size / DEV_BSIZE);
 2108         }
 2109 
 2110         if (error)
 2111                 vrele(vp);
 2112 done:
 2113         swdev_syscall_active = 0;
 2114         wakeup_one(&swdev_syscall_active);
 2115 done2:
 2116         mtx_unlock(&Giant);
 2117         return (error);
 2118 }
 2119 
 2120 static void
 2121 swaponsomething(struct vnode *vp, void *id, u_long nblks, sw_strategy_t *strategy, sw_close_t *close, udev_t udev)
 2122 {
 2123         struct swdevt *sp, *tsp;
 2124         swblk_t dvbase;
 2125         u_long mblocks;
 2126 
 2127         /*
 2128          * If we go beyond this, we get overflows in the radix
 2129          * tree bitmap code.
 2130          */
 2131         mblocks = 0x40000000 / BLIST_META_RADIX;
 2132         if (nblks > mblocks) {
 2133                 printf("WARNING: reducing size to maximum of %lu blocks per swap unit\n",
 2134                         mblocks);
 2135                 nblks = mblocks;
 2136         }
 2137         /*
 2138          * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks.
 2139          * First chop nblks off to page-align it, then convert.
 2140          * 
 2141          * sw->sw_nblks is in page-sized chunks now too.
 2142          */
 2143         nblks &= ~(ctodb(1) - 1);
 2144         nblks = dbtoc(nblks);
 2145 
 2146         sp = malloc(sizeof *sp, M_VMPGDATA, M_WAITOK | M_ZERO);
 2147         sp->sw_vp = vp;
 2148         sp->sw_id = id;
 2149         sp->sw_udev = udev;
 2150         sp->sw_flags = 0;
 2151         sp->sw_nblks = nblks;
 2152         sp->sw_used = 0;
 2153         sp->sw_strategy = strategy;
 2154         sp->sw_close = close;
 2155 
 2156         sp->sw_blist = blist_create(nblks);
 2157         /*
 2158          * Do not free the first two block in order to avoid overwriting
 2159          * any bsd label at the front of the partition
 2160          */
 2161         blist_free(sp->sw_blist, 2, nblks - 2);
 2162 
 2163         dvbase = 0;
 2164         mtx_lock(&sw_dev_mtx);
 2165         TAILQ_FOREACH(tsp, &swtailq, sw_list) {
 2166                 if (tsp->sw_end >= dvbase) {
 2167                         /*
 2168                          * We put one uncovered page between the devices
 2169                          * in order to definitively prevent any cross-device
 2170                          * I/O requests
 2171                          */
 2172                         dvbase = tsp->sw_end + 1;
 2173                 }
 2174         }
 2175         sp->sw_first = dvbase;
 2176         sp->sw_end = dvbase + nblks;
 2177         TAILQ_INSERT_TAIL(&swtailq, sp, sw_list);
 2178         nswapdev++;
 2179         swap_pager_avail += nblks;
 2180         swp_sizecheck();
 2181         mtx_unlock(&sw_dev_mtx);
 2182 }
 2183 
 2184 /*
 2185  * SYSCALL: swapoff(devname)
 2186  *
 2187  * Disable swapping on the given device.
 2188  *
 2189  * XXX: Badly designed system call: it should use a device index
 2190  * rather than filename as specification.  We keep sw_vp around
 2191  * only to make this work.
 2192  */
 2193 #ifndef _SYS_SYSPROTO_H_
 2194 struct swapoff_args {
 2195         char *name;
 2196 };
 2197 #endif
 2198 
 2199 /*
 2200  * MPSAFE
 2201  */
 2202 /* ARGSUSED */
 2203 int
 2204 swapoff(struct thread *td, struct swapoff_args *uap)
 2205 {
 2206         struct vnode *vp;
 2207         struct nameidata nd;
 2208         struct swdevt *sp;
 2209         u_long nblks, dvbase;
 2210         int error;
 2211 
 2212         mtx_lock(&Giant);
 2213 
 2214         error = suser(td);
 2215         if (error)
 2216                 goto done2;
 2217 
 2218         while (swdev_syscall_active)
 2219             tsleep(&swdev_syscall_active, PUSER - 1, "swpoff", 0);
 2220         swdev_syscall_active = 1;
 2221 
 2222         NDINIT(&nd, LOOKUP, FOLLOW, UIO_USERSPACE, uap->name, td);
 2223         error = namei(&nd);
 2224         if (error)
 2225                 goto done;
 2226         NDFREE(&nd, NDF_ONLY_PNBUF);
 2227         vp = nd.ni_vp;
 2228 
 2229         mtx_lock(&sw_dev_mtx);
 2230         TAILQ_FOREACH(sp, &swtailq, sw_list) {
 2231                 if (sp->sw_vp == vp)
 2232                         goto found;
 2233         }
 2234         mtx_unlock(&sw_dev_mtx);
 2235         error = EINVAL;
 2236         goto done;
 2237 found:
 2238         mtx_unlock(&sw_dev_mtx);
 2239 #ifdef MAC
 2240         (void) vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
 2241         error = mac_check_system_swapoff(td->td_ucred, vp);
 2242         (void) VOP_UNLOCK(vp, 0, td);
 2243         if (error != 0)
 2244                 goto done;
 2245 #endif
 2246         
 2247         nblks = sp->sw_nblks;
 2248 
 2249         /*
 2250          * We can turn off this swap device safely only if the
 2251          * available virtual memory in the system will fit the amount
 2252          * of data we will have to page back in, plus an epsilon so
 2253          * the system doesn't become critically low on swap space.
 2254          */
 2255         if (cnt.v_free_count + cnt.v_cache_count + swap_pager_avail <
 2256             nblks + nswap_lowat) {
 2257                 error = ENOMEM;
 2258                 goto done;
 2259         }
 2260 
 2261         /*
 2262          * Prevent further allocations on this device.
 2263          */
 2264         mtx_lock(&sw_dev_mtx);
 2265         sp->sw_flags |= SW_CLOSING;
 2266         for (dvbase = 0; dvbase < sp->sw_end; dvbase += dmmax) {
 2267                 swap_pager_avail -= blist_fill(sp->sw_blist,
 2268                      dvbase, dmmax);
 2269         }
 2270         mtx_unlock(&sw_dev_mtx);
 2271 
 2272         /*
 2273          * Page in the contents of the device and close it.
 2274          */
 2275 #ifndef NO_SWAPPING
 2276         vm_proc_swapin_all(sp);
 2277 #endif /* !NO_SWAPPING */
 2278         swap_pager_swapoff(sp, &sp->sw_used);
 2279 
 2280         sp->sw_close(td, sp);
 2281         sp->sw_id = NULL;
 2282         mtx_lock(&sw_dev_mtx);
 2283         TAILQ_REMOVE(&swtailq, sp, sw_list);
 2284         nswapdev--;
 2285         if (swdevhd == sp)
 2286                 swdevhd = NULL;
 2287         mtx_unlock(&sw_dev_mtx);
 2288         blist_destroy(sp->sw_blist);
 2289         free(sp, M_VMPGDATA);
 2290 
 2291 done:
 2292         swdev_syscall_active = 0;
 2293         wakeup_one(&swdev_syscall_active);
 2294 done2:
 2295         mtx_unlock(&Giant);
 2296         return (error);
 2297 }
 2298 
 2299 void
 2300 swap_pager_status(int *total, int *used)
 2301 {
 2302         struct swdevt *sp;
 2303 
 2304         *total = 0;
 2305         *used = 0;
 2306         mtx_lock(&sw_dev_mtx);
 2307         TAILQ_FOREACH(sp, &swtailq, sw_list) {
 2308                 *total += sp->sw_nblks;
 2309                 *used += sp->sw_used;
 2310         }
 2311         mtx_unlock(&sw_dev_mtx);
 2312 }
 2313 
 2314 static int
 2315 sysctl_vm_swap_info(SYSCTL_HANDLER_ARGS)
 2316 {
 2317         int     *name = (int *)arg1;
 2318         int     error, n;
 2319         struct xswdev xs;
 2320         struct swdevt *sp;
 2321 
 2322         if (arg2 != 1) /* name length */
 2323                 return (EINVAL);
 2324 
 2325         n = 0;
 2326         mtx_lock(&sw_dev_mtx);
 2327         TAILQ_FOREACH(sp, &swtailq, sw_list) {
 2328                 if (n == *name) {
 2329                         mtx_unlock(&sw_dev_mtx);
 2330                         xs.xsw_version = XSWDEV_VERSION;
 2331                         xs.xsw_dev = sp->sw_udev;
 2332                         xs.xsw_flags = sp->sw_flags;
 2333                         xs.xsw_nblks = sp->sw_nblks;
 2334                         xs.xsw_used = sp->sw_used;
 2335 
 2336                         error = SYSCTL_OUT(req, &xs, sizeof(xs));
 2337                         return (error);
 2338                 }
 2339                 n++;
 2340         }
 2341         mtx_unlock(&sw_dev_mtx);
 2342         return (ENOENT);
 2343 }
 2344 
 2345 SYSCTL_INT(_vm, OID_AUTO, nswapdev, CTLFLAG_RD, &nswapdev, 0,
 2346     "Number of swap devices");
 2347 SYSCTL_NODE(_vm, OID_AUTO, swap_info, CTLFLAG_RD, sysctl_vm_swap_info,
 2348     "Swap statistics by device");
 2349 
 2350 /*
 2351  * vmspace_swap_count() - count the approximate swap useage in pages for a
 2352  *                        vmspace.
 2353  *
 2354  *      The map must be locked.
 2355  *
 2356  *      Swap useage is determined by taking the proportional swap used by
 2357  *      VM objects backing the VM map.  To make up for fractional losses,
 2358  *      if the VM object has any swap use at all the associated map entries
 2359  *      count for at least 1 swap page.
 2360  */
 2361 int
 2362 vmspace_swap_count(struct vmspace *vmspace)
 2363 {
 2364         vm_map_t map = &vmspace->vm_map;
 2365         vm_map_entry_t cur;
 2366         int count = 0;
 2367 
 2368         for (cur = map->header.next; cur != &map->header; cur = cur->next) {
 2369                 vm_object_t object;
 2370 
 2371                 if ((cur->eflags & MAP_ENTRY_IS_SUB_MAP) == 0 &&
 2372                     (object = cur->object.vm_object) != NULL) {
 2373                         VM_OBJECT_LOCK(object);
 2374                         if (object->type == OBJT_SWAP &&
 2375                             object->un_pager.swp.swp_bcount != 0) {
 2376                                 int n = (cur->end - cur->start) / PAGE_SIZE;
 2377 
 2378                                 count += object->un_pager.swp.swp_bcount *
 2379                                     SWAP_META_PAGES * n / object->size + 1;
 2380                         }
 2381                         VM_OBJECT_UNLOCK(object);
 2382                 }
 2383         }
 2384         return (count);
 2385 }
 2386 
 2387 /*
 2388  * GEOM backend
 2389  *
 2390  * Swapping onto disk devices.
 2391  *
 2392  */
 2393 
 2394 static struct g_class g_swap_class = {
 2395         .name = "SWAP",
 2396 };
 2397 
 2398 DECLARE_GEOM_CLASS(g_swap_class, g_class);
 2399 
 2400 
 2401 static void
 2402 swapgeom_done(struct bio *bp2)
 2403 {
 2404         struct buf *bp;
 2405 
 2406         bp = bp2->bio_caller2;
 2407         if (bp2->bio_error)
 2408                 bp->b_ioflags |= BIO_ERROR;
 2409         mtx_lock(&Giant);
 2410         bufdone(bp);
 2411         mtx_unlock(&Giant);
 2412         g_destroy_bio(bp2);
 2413 }
 2414 
 2415 static void
 2416 swapgeom_strategy(struct buf *bp, struct swdevt *sp)
 2417 {
 2418         struct bio *bio;
 2419         struct g_consumer *cp;
 2420 
 2421         cp = sp->sw_id;
 2422         if (cp == NULL) {
 2423                 bp->b_error = ENXIO;
 2424                 bp->b_ioflags |= BIO_ERROR;
 2425                 bufdone(bp);
 2426                 return;
 2427         }
 2428         bio = g_clone_bio(&bp->b_io);
 2429         bio->bio_caller2 = bp;
 2430         bio->bio_offset = (bp->b_blkno - sp->sw_first) * PAGE_SIZE;
 2431         bio->bio_length = bp->b_bcount;
 2432         bio->bio_done = swapgeom_done;
 2433         g_io_request(bio, cp);
 2434         return;
 2435 }
 2436 
 2437 static void
 2438 swapgeom_orphan(struct g_consumer *cp)
 2439 {
 2440         struct swdevt *sp;
 2441 
 2442         mtx_lock(&sw_dev_mtx);
 2443         TAILQ_FOREACH(sp, &swtailq, sw_list)
 2444                 if (sp->sw_id == cp)
 2445                         sp->sw_id = NULL;
 2446         mtx_unlock(&sw_dev_mtx);
 2447 }
 2448 
 2449 static void
 2450 swapgeom_close_ev(void *arg, int flags)
 2451 {
 2452         struct g_consumer *cp;
 2453 
 2454         cp = arg;
 2455         g_access_rel(cp, -1, -1, 0);
 2456         g_detach(cp);
 2457         g_destroy_consumer(cp);
 2458 }
 2459 
 2460 static void
 2461 swapgeom_close(struct thread *td, struct swdevt *sw)
 2462 {
 2463 
 2464         /* XXX: direct call when Giant untangled */
 2465         g_waitfor_event(swapgeom_close_ev, sw->sw_id, M_WAITOK, NULL);
 2466 }
 2467 
 2468 
 2469 struct swh0h0 {
 2470         dev_t   dev;
 2471         struct vnode *vp;
 2472         int     error;
 2473 };
 2474 
 2475 static void
 2476 swapongeom_ev(void *arg, int flags)
 2477 {
 2478         struct swh0h0 *swh;
 2479         struct g_provider *pp;
 2480         struct g_consumer *cp;
 2481         static struct g_geom *gp;
 2482         struct swdevt *sp;
 2483         u_long nblks;
 2484         int error;
 2485 
 2486         swh = arg;
 2487         swh->error = 0;
 2488         pp = g_dev_getprovider(swh->dev);
 2489         if (pp == NULL) {
 2490                 swh->error = ENODEV;
 2491                 return;
 2492         }
 2493         mtx_lock(&sw_dev_mtx);
 2494         TAILQ_FOREACH(sp, &swtailq, sw_list) {
 2495                 cp = sp->sw_id;
 2496                 if (cp != NULL && cp->provider == pp) {
 2497                         mtx_unlock(&sw_dev_mtx);
 2498                         swh->error = EBUSY;
 2499                         return;
 2500                 }
 2501         }
 2502         mtx_unlock(&sw_dev_mtx);
 2503         if (gp == NULL) {
 2504                 gp = g_new_geomf(&g_swap_class, "swap", NULL);
 2505                 gp->orphan = swapgeom_orphan;
 2506         }
 2507         cp = g_new_consumer(gp);
 2508         g_attach(cp, pp);
 2509         /*
 2510          * XXX: Everytime you think you can improve the margin for
 2511          * footshooting, somebody depends on the ability to do so:
 2512          * savecore(8) wants to write to our swapdev so we cannot
 2513          * set an exclusive count :-(
 2514          */
 2515         error = g_access_rel(cp, 1, 1, 0);
 2516         if (error) {
 2517                 g_detach(cp);
 2518                 g_destroy_consumer(cp);
 2519                 swh->error = error;
 2520                 return;
 2521         }
 2522         nblks = pp->mediasize / DEV_BSIZE;
 2523         swaponsomething(swh->vp, cp, nblks, swapgeom_strategy,
 2524             swapgeom_close, dev2udev(swh->dev));
 2525         swh->error = 0;
 2526         return;
 2527 }
 2528 
 2529 static int
 2530 swapongeom(struct thread *td, struct vnode *vp)
 2531 {
 2532         int error;
 2533         struct swh0h0 swh;
 2534 
 2535         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
 2536 
 2537         swh.dev = vp->v_rdev;
 2538         swh.vp = vp;
 2539         swh.error = 0;
 2540         /* XXX: direct call when Giant untangled */
 2541         error = g_waitfor_event(swapongeom_ev, &swh, M_WAITOK, NULL);
 2542         if (!error)
 2543                 error = swh.error;
 2544         VOP_UNLOCK(vp, 0, td);
 2545         return (error);
 2546 }
 2547 
 2548 /*
 2549  * VNODE backend
 2550  *
 2551  * This is used mainly for network filesystem (read: probably only tested
 2552  * with NFS) swapfiles.
 2553  *
 2554  */
 2555 
 2556 static void
 2557 swapdev_strategy(struct buf *bp, struct swdevt *sp)
 2558 {
 2559         int s;
 2560         struct vnode *vp, *vp2;
 2561 
 2562         bp->b_dev = NODEV;
 2563         bp->b_blkno = ctodb(bp->b_blkno - sp->sw_first);
 2564 
 2565         vp2 = sp->sw_id;
 2566         vhold(vp2);
 2567         s = splvm();
 2568         if (bp->b_iocmd == BIO_WRITE) {
 2569                 vp = bp->b_vp;
 2570                 if (vp) {
 2571                         VI_LOCK(vp);
 2572                         vp->v_numoutput--;
 2573                         if ((vp->v_iflag & VI_BWAIT) && vp->v_numoutput <= 0) {
 2574                                 vp->v_iflag &= ~VI_BWAIT;
 2575                                 wakeup(&vp->v_numoutput);
 2576                         }
 2577                         VI_UNLOCK(vp);
 2578                 }
 2579                 VI_LOCK(vp2);
 2580                 vp2->v_numoutput++;
 2581                 VI_UNLOCK(vp2);
 2582         }
 2583         bp->b_vp = vp2;
 2584         splx(s);
 2585         bp->b_iooffset = dbtob(bp->b_blkno);
 2586         VOP_STRATEGY(vp2, bp);
 2587         return;
 2588 }
 2589 
 2590 static void
 2591 swapdev_close(struct thread *td, struct swdevt *sp)
 2592 {
 2593 
 2594         VOP_CLOSE(sp->sw_vp, FREAD | FWRITE, td->td_ucred, td);
 2595         vrele(sp->sw_vp);
 2596 }
 2597 
 2598 
 2599 static int
 2600 swaponvp(struct thread *td, struct vnode *vp, u_long nblks)
 2601 {
 2602         struct swdevt *sp;
 2603         int error;
 2604 
 2605         if (nblks == 0)
 2606                 return (ENXIO);
 2607         mtx_lock(&sw_dev_mtx);
 2608         TAILQ_FOREACH(sp, &swtailq, sw_list) {
 2609                 if (sp->sw_id == vp) {
 2610                         mtx_unlock(&sw_dev_mtx);
 2611                         return (EBUSY);
 2612                 }
 2613         }
 2614         mtx_unlock(&sw_dev_mtx);
 2615     
 2616         (void) vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
 2617 #ifdef MAC
 2618         error = mac_check_system_swapon(td->td_ucred, vp);
 2619         if (error == 0)
 2620 #endif
 2621                 error = VOP_OPEN(vp, FREAD | FWRITE, td->td_ucred, td, -1);
 2622         (void) VOP_UNLOCK(vp, 0, td);
 2623         if (error)
 2624                 return (error);
 2625 
 2626         swaponsomething(vp, vp, nblks, swapdev_strategy, swapdev_close,
 2627             NOUDEV);
 2628         return (0);
 2629 }

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