The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_fault.c

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    1 /*-
    2  * Copyright (c) 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * Copyright (c) 1994 John S. Dyson
    5  * All rights reserved.
    6  * Copyright (c) 1994 David Greenman
    7  * All rights reserved.
    8  *
    9  *
   10  * This code is derived from software contributed to Berkeley by
   11  * The Mach Operating System project at Carnegie-Mellon University.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  * 3. All advertising materials mentioning features or use of this software
   22  *    must display the following acknowledgement:
   23  *      This product includes software developed by the University of
   24  *      California, Berkeley and its contributors.
   25  * 4. Neither the name of the University nor the names of its contributors
   26  *    may be used to endorse or promote products derived from this software
   27  *    without specific prior written permission.
   28  *
   29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   39  * SUCH DAMAGE.
   40  *
   41  *      from: @(#)vm_fault.c    8.4 (Berkeley) 1/12/94
   42  *
   43  *
   44  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
   45  * All rights reserved.
   46  *
   47  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
   48  *
   49  * Permission to use, copy, modify and distribute this software and
   50  * its documentation is hereby granted, provided that both the copyright
   51  * notice and this permission notice appear in all copies of the
   52  * software, derivative works or modified versions, and any portions
   53  * thereof, and that both notices appear in supporting documentation.
   54  *
   55  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   56  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
   57  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   58  *
   59  * Carnegie Mellon requests users of this software to return to
   60  *
   61  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   62  *  School of Computer Science
   63  *  Carnegie Mellon University
   64  *  Pittsburgh PA 15213-3890
   65  *
   66  * any improvements or extensions that they make and grant Carnegie the
   67  * rights to redistribute these changes.
   68  */
   69 
   70 /*
   71  *      Page fault handling module.
   72  */
   73 
   74 #include <sys/cdefs.h>
   75 __FBSDID("$FreeBSD: releng/6.0/sys/vm/vm_fault.c 151118 2005-10-09 03:08:28Z delphij $");
   76 
   77 #include <sys/param.h>
   78 #include <sys/systm.h>
   79 #include <sys/kernel.h>
   80 #include <sys/lock.h>
   81 #include <sys/mutex.h>
   82 #include <sys/proc.h>
   83 #include <sys/resourcevar.h>
   84 #include <sys/sysctl.h>
   85 #include <sys/vmmeter.h>
   86 #include <sys/vnode.h>
   87 
   88 #include <vm/vm.h>
   89 #include <vm/vm_param.h>
   90 #include <vm/pmap.h>
   91 #include <vm/vm_map.h>
   92 #include <vm/vm_object.h>
   93 #include <vm/vm_page.h>
   94 #include <vm/vm_pageout.h>
   95 #include <vm/vm_kern.h>
   96 #include <vm/vm_pager.h>
   97 #include <vm/vnode_pager.h>
   98 #include <vm/vm_extern.h>
   99 
  100 #include <sys/mount.h>  /* XXX Temporary for VFS_LOCK_GIANT() */
  101 
  102 #define PFBAK 4
  103 #define PFFOR 4
  104 #define PAGEORDER_SIZE (PFBAK+PFFOR)
  105 
  106 static int prefault_pageorder[] = {
  107         -1 * PAGE_SIZE, 1 * PAGE_SIZE,
  108         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
  109         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
  110         -4 * PAGE_SIZE, 4 * PAGE_SIZE
  111 };
  112 
  113 static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
  114 static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
  115 
  116 #define VM_FAULT_READ_AHEAD 8
  117 #define VM_FAULT_READ_BEHIND 7
  118 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
  119 
  120 struct faultstate {
  121         vm_page_t m;
  122         vm_object_t object;
  123         vm_pindex_t pindex;
  124         vm_page_t first_m;
  125         vm_object_t     first_object;
  126         vm_pindex_t first_pindex;
  127         vm_map_t map;
  128         vm_map_entry_t entry;
  129         int lookup_still_valid;
  130         struct vnode *vp;
  131 };
  132 
  133 static __inline void
  134 release_page(struct faultstate *fs)
  135 {
  136         vm_page_lock_queues();
  137         vm_page_wakeup(fs->m);
  138         vm_page_deactivate(fs->m);
  139         vm_page_unlock_queues();
  140         fs->m = NULL;
  141 }
  142 
  143 static __inline void
  144 unlock_map(struct faultstate *fs)
  145 {
  146         if (fs->lookup_still_valid) {
  147                 vm_map_lookup_done(fs->map, fs->entry);
  148                 fs->lookup_still_valid = FALSE;
  149         }
  150 }
  151 
  152 static void
  153 unlock_and_deallocate(struct faultstate *fs)
  154 {
  155 
  156         vm_object_pip_wakeup(fs->object);
  157         VM_OBJECT_UNLOCK(fs->object);
  158         if (fs->object != fs->first_object) {
  159                 VM_OBJECT_LOCK(fs->first_object);
  160                 vm_page_lock_queues();
  161                 vm_page_free(fs->first_m);
  162                 vm_page_unlock_queues();
  163                 vm_object_pip_wakeup(fs->first_object);
  164                 VM_OBJECT_UNLOCK(fs->first_object);
  165                 fs->first_m = NULL;
  166         }
  167         vm_object_deallocate(fs->first_object);
  168         unlock_map(fs); 
  169         if (fs->vp != NULL) { 
  170                 int vfslocked;
  171 
  172                 vfslocked = VFS_LOCK_GIANT(fs->vp->v_mount);
  173                 vput(fs->vp);
  174                 fs->vp = NULL;
  175                 VFS_UNLOCK_GIANT(vfslocked);
  176         }
  177         if (fs->first_object->flags & OBJ_NEEDGIANT)
  178                 VM_UNLOCK_GIANT();
  179 }
  180 
  181 /*
  182  * TRYPAGER - used by vm_fault to calculate whether the pager for the
  183  *            current object *might* contain the page.
  184  *
  185  *            default objects are zero-fill, there is no real pager.
  186  */
  187 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
  188                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
  189 
  190 /*
  191  *      vm_fault:
  192  *
  193  *      Handle a page fault occurring at the given address,
  194  *      requiring the given permissions, in the map specified.
  195  *      If successful, the page is inserted into the
  196  *      associated physical map.
  197  *
  198  *      NOTE: the given address should be truncated to the
  199  *      proper page address.
  200  *
  201  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
  202  *      a standard error specifying why the fault is fatal is returned.
  203  *
  204  *
  205  *      The map in question must be referenced, and remains so.
  206  *      Caller may hold no locks.
  207  */
  208 int
  209 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
  210          int fault_flags)
  211 {
  212         vm_prot_t prot;
  213         int is_first_object_locked, result;
  214         boolean_t growstack, wired;
  215         int map_generation;
  216         vm_object_t next_object;
  217         vm_page_t marray[VM_FAULT_READ];
  218         int hardfault;
  219         int faultcount;
  220         struct faultstate fs;
  221 
  222         hardfault = 0;
  223         growstack = TRUE;
  224         atomic_add_int(&cnt.v_vm_faults, 1);
  225 
  226 RetryFault:;
  227 
  228         /*
  229          * Find the backing store object and offset into it to begin the
  230          * search.
  231          */
  232         fs.map = map;
  233         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
  234             &fs.first_object, &fs.first_pindex, &prot, &wired);
  235         if (result != KERN_SUCCESS) {
  236                 if (result != KERN_PROTECTION_FAILURE ||
  237                     (fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE) {
  238                         if (growstack && result == KERN_INVALID_ADDRESS &&
  239                             map != kernel_map && curproc != NULL) {
  240                                 result = vm_map_growstack(curproc, vaddr);
  241                                 if (result != KERN_SUCCESS)
  242                                         return (KERN_FAILURE);
  243                                 growstack = FALSE;
  244                                 goto RetryFault;
  245                         }
  246                         return (result);
  247                 }
  248 
  249                 /*
  250                  * If we are user-wiring a r/w segment, and it is COW, then
  251                  * we need to do the COW operation.  Note that we don't COW
  252                  * currently RO sections now, because it is NOT desirable
  253                  * to COW .text.  We simply keep .text from ever being COW'ed
  254                  * and take the heat that one cannot debug wired .text sections.
  255                  */
  256                 result = vm_map_lookup(&fs.map, vaddr,
  257                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
  258                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
  259                 if (result != KERN_SUCCESS)
  260                         return (result);
  261 
  262                 /*
  263                  * If we don't COW now, on a user wire, the user will never
  264                  * be able to write to the mapping.  If we don't make this
  265                  * restriction, the bookkeeping would be nearly impossible.
  266                  *
  267                  * XXX The following assignment modifies the map without
  268                  * holding a write lock on it.
  269                  */
  270                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
  271                         fs.entry->max_protection &= ~VM_PROT_WRITE;
  272         }
  273 
  274         map_generation = fs.map->timestamp;
  275 
  276         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
  277                 panic("vm_fault: fault on nofault entry, addr: %lx",
  278                     (u_long)vaddr);
  279         }
  280 
  281         /*
  282          * Make a reference to this object to prevent its disposal while we
  283          * are messing with it.  Once we have the reference, the map is free
  284          * to be diddled.  Since objects reference their shadows (and copies),
  285          * they will stay around as well.
  286          *
  287          * Bump the paging-in-progress count to prevent size changes (e.g. 
  288          * truncation operations) during I/O.  This must be done after
  289          * obtaining the vnode lock in order to avoid possible deadlocks.
  290          *
  291          * XXX vnode_pager_lock() can block without releasing the map lock.
  292          */
  293         if (fs.first_object->flags & OBJ_NEEDGIANT)
  294                 mtx_lock(&Giant);
  295         VM_OBJECT_LOCK(fs.first_object);
  296         vm_object_reference_locked(fs.first_object);
  297         fs.vp = vnode_pager_lock(fs.first_object);
  298         KASSERT(fs.vp == NULL || !fs.map->system_map,
  299             ("vm_fault: vnode-backed object mapped by system map"));
  300         KASSERT((fs.first_object->flags & OBJ_NEEDGIANT) == 0 ||
  301             !fs.map->system_map,
  302             ("vm_fault: Object requiring giant mapped by system map"));
  303         if (fs.first_object->flags & OBJ_NEEDGIANT && debug_mpsafevm)
  304                 mtx_unlock(&Giant);
  305         vm_object_pip_add(fs.first_object, 1);
  306 
  307         fs.lookup_still_valid = TRUE;
  308 
  309         if (wired)
  310                 fault_type = prot;
  311 
  312         fs.first_m = NULL;
  313 
  314         /*
  315          * Search for the page at object/offset.
  316          */
  317         fs.object = fs.first_object;
  318         fs.pindex = fs.first_pindex;
  319         while (TRUE) {
  320                 /*
  321                  * If the object is dead, we stop here
  322                  */
  323                 if (fs.object->flags & OBJ_DEAD) {
  324                         unlock_and_deallocate(&fs);
  325                         return (KERN_PROTECTION_FAILURE);
  326                 }
  327 
  328                 /*
  329                  * See if page is resident
  330                  */
  331                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  332                 if (fs.m != NULL) {
  333                         int queue;
  334 
  335                         /* 
  336                          * check for page-based copy on write.
  337                          * We check fs.object == fs.first_object so
  338                          * as to ensure the legacy COW mechanism is
  339                          * used when the page in question is part of
  340                          * a shadow object.  Otherwise, vm_page_cowfault()
  341                          * removes the page from the backing object, 
  342                          * which is not what we want.
  343                          */
  344                         vm_page_lock_queues();
  345                         if ((fs.m->cow) && 
  346                             (fault_type & VM_PROT_WRITE) &&
  347                             (fs.object == fs.first_object)) {
  348                                 vm_page_cowfault(fs.m);
  349                                 vm_page_unlock_queues();
  350                                 unlock_and_deallocate(&fs);
  351                                 goto RetryFault;
  352                         }
  353 
  354                         /*
  355                          * Wait/Retry if the page is busy.  We have to do this
  356                          * if the page is busy via either PG_BUSY or 
  357                          * vm_page_t->busy because the vm_pager may be using
  358                          * vm_page_t->busy for pageouts ( and even pageins if
  359                          * it is the vnode pager ), and we could end up trying
  360                          * to pagein and pageout the same page simultaneously.
  361                          *
  362                          * We can theoretically allow the busy case on a read
  363                          * fault if the page is marked valid, but since such
  364                          * pages are typically already pmap'd, putting that
  365                          * special case in might be more effort then it is 
  366                          * worth.  We cannot under any circumstances mess
  367                          * around with a vm_page_t->busy page except, perhaps,
  368                          * to pmap it.
  369                          */
  370                         if ((fs.m->flags & PG_BUSY) || fs.m->busy) {
  371                                 vm_page_unlock_queues();
  372                                 VM_OBJECT_UNLOCK(fs.object);
  373                                 if (fs.object != fs.first_object) {
  374                                         VM_OBJECT_LOCK(fs.first_object);
  375                                         vm_page_lock_queues();
  376                                         vm_page_free(fs.first_m);
  377                                         vm_page_unlock_queues();
  378                                         vm_object_pip_wakeup(fs.first_object);
  379                                         VM_OBJECT_UNLOCK(fs.first_object);
  380                                         fs.first_m = NULL;
  381                                 }
  382                                 unlock_map(&fs);
  383                                 if (fs.vp != NULL) {
  384                                         int vfslck;
  385 
  386                                         vfslck = VFS_LOCK_GIANT(fs.vp->v_mount);
  387                                         vput(fs.vp);
  388                                         fs.vp = NULL;
  389                                         VFS_UNLOCK_GIANT(vfslck);
  390                                 }
  391                                 VM_OBJECT_LOCK(fs.object);
  392                                 if (fs.m == vm_page_lookup(fs.object,
  393                                     fs.pindex)) {
  394                                         vm_page_lock_queues();
  395                                         if (!vm_page_sleep_if_busy(fs.m, TRUE,
  396                                             "vmpfw"))
  397                                                 vm_page_unlock_queues();
  398                                 }
  399                                 vm_object_pip_wakeup(fs.object);
  400                                 VM_OBJECT_UNLOCK(fs.object);
  401                                 atomic_add_int(&cnt.v_intrans, 1);
  402                                 if (fs.first_object->flags & OBJ_NEEDGIANT)
  403                                         VM_UNLOCK_GIANT();
  404                                 vm_object_deallocate(fs.first_object);
  405                                 goto RetryFault;
  406                         }
  407                         queue = fs.m->queue;
  408 
  409                         vm_pageq_remove_nowakeup(fs.m);
  410 
  411                         if ((queue - fs.m->pc) == PQ_CACHE && vm_page_count_severe()) {
  412                                 vm_page_activate(fs.m);
  413                                 vm_page_unlock_queues();
  414                                 unlock_and_deallocate(&fs);
  415                                 VM_WAITPFAULT;
  416                                 goto RetryFault;
  417                         }
  418 
  419                         /*
  420                          * Mark page busy for other processes, and the 
  421                          * pagedaemon.  If it still isn't completely valid
  422                          * (readable), jump to readrest, else break-out ( we
  423                          * found the page ).
  424                          */
  425                         vm_page_busy(fs.m);
  426                         vm_page_unlock_queues();
  427                         if (((fs.m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) &&
  428                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
  429                                 goto readrest;
  430                         }
  431 
  432                         break;
  433                 }
  434 
  435                 /*
  436                  * Page is not resident, If this is the search termination
  437                  * or the pager might contain the page, allocate a new page.
  438                  */
  439                 if (TRYPAGER || fs.object == fs.first_object) {
  440                         if (fs.pindex >= fs.object->size) {
  441                                 unlock_and_deallocate(&fs);
  442                                 return (KERN_PROTECTION_FAILURE);
  443                         }
  444 
  445                         /*
  446                          * Allocate a new page for this object/offset pair.
  447                          */
  448                         fs.m = NULL;
  449                         if (!vm_page_count_severe()) {
  450                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
  451                                     (fs.vp || fs.object->backing_object)? VM_ALLOC_NORMAL: VM_ALLOC_ZERO);
  452                         }
  453                         if (fs.m == NULL) {
  454                                 unlock_and_deallocate(&fs);
  455                                 VM_WAITPFAULT;
  456                                 goto RetryFault;
  457                         }
  458                 }
  459 
  460 readrest:
  461                 /*
  462                  * We have found a valid page or we have allocated a new page.
  463                  * The page thus may not be valid or may not be entirely 
  464                  * valid.
  465                  *
  466                  * Attempt to fault-in the page if there is a chance that the
  467                  * pager has it, and potentially fault in additional pages
  468                  * at the same time.
  469                  */
  470                 if (TRYPAGER) {
  471                         int rv;
  472                         int reqpage;
  473                         int ahead, behind;
  474                         u_char behavior = vm_map_entry_behavior(fs.entry);
  475 
  476                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
  477                                 ahead = 0;
  478                                 behind = 0;
  479                         } else {
  480                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
  481                                 if (behind > VM_FAULT_READ_BEHIND)
  482                                         behind = VM_FAULT_READ_BEHIND;
  483 
  484                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
  485                                 if (ahead > VM_FAULT_READ_AHEAD)
  486                                         ahead = VM_FAULT_READ_AHEAD;
  487                         }
  488                         is_first_object_locked = FALSE;
  489                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
  490                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
  491                               fs.pindex >= fs.entry->lastr &&
  492                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
  493                             (fs.first_object == fs.object ||
  494                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
  495                             fs.first_object->type != OBJT_DEVICE) {
  496                                 vm_pindex_t firstpindex, tmppindex;
  497 
  498                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
  499                                         firstpindex = 0;
  500                                 else
  501                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
  502 
  503                                 vm_page_lock_queues();
  504                                 /*
  505                                  * note: partially valid pages cannot be 
  506                                  * included in the lookahead - NFS piecemeal
  507                                  * writes will barf on it badly.
  508                                  */
  509                                 for (tmppindex = fs.first_pindex - 1;
  510                                         tmppindex >= firstpindex;
  511                                         --tmppindex) {
  512                                         vm_page_t mt;
  513 
  514                                         mt = vm_page_lookup(fs.first_object, tmppindex);
  515                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
  516                                                 break;
  517                                         if (mt->busy ||
  518                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
  519                                                 mt->hold_count ||
  520                                                 mt->wire_count) 
  521                                                 continue;
  522                                         pmap_remove_all(mt);
  523                                         if (mt->dirty) {
  524                                                 vm_page_deactivate(mt);
  525                                         } else {
  526                                                 vm_page_cache(mt);
  527                                         }
  528                                 }
  529                                 vm_page_unlock_queues();
  530                                 ahead += behind;
  531                                 behind = 0;
  532                         }
  533                         if (is_first_object_locked)
  534                                 VM_OBJECT_UNLOCK(fs.first_object);
  535                         /*
  536                          * now we find out if any other pages should be paged
  537                          * in at this time this routine checks to see if the
  538                          * pages surrounding this fault reside in the same
  539                          * object as the page for this fault.  If they do,
  540                          * then they are faulted in also into the object.  The
  541                          * array "marray" returned contains an array of
  542                          * vm_page_t structs where one of them is the
  543                          * vm_page_t passed to the routine.  The reqpage
  544                          * return value is the index into the marray for the
  545                          * vm_page_t passed to the routine.
  546                          *
  547                          * fs.m plus the additional pages are PG_BUSY'd.
  548                          *
  549                          * XXX vm_fault_additional_pages() can block
  550                          * without releasing the map lock.
  551                          */
  552                         faultcount = vm_fault_additional_pages(
  553                             fs.m, behind, ahead, marray, &reqpage);
  554 
  555                         /*
  556                          * update lastr imperfectly (we do not know how much
  557                          * getpages will actually read), but good enough.
  558                          *
  559                          * XXX The following assignment modifies the map
  560                          * without holding a write lock on it.
  561                          */
  562                         fs.entry->lastr = fs.pindex + faultcount - behind;
  563 
  564                         /*
  565                          * Call the pager to retrieve the data, if any, after
  566                          * releasing the lock on the map.  We hold a ref on
  567                          * fs.object and the pages are PG_BUSY'd.
  568                          */
  569                         unlock_map(&fs);
  570 
  571                         rv = faultcount ?
  572                             vm_pager_get_pages(fs.object, marray, faultcount,
  573                                 reqpage) : VM_PAGER_FAIL;
  574 
  575                         if (rv == VM_PAGER_OK) {
  576                                 /*
  577                                  * Found the page. Leave it busy while we play
  578                                  * with it.
  579                                  */
  580 
  581                                 /*
  582                                  * Relookup in case pager changed page. Pager
  583                                  * is responsible for disposition of old page
  584                                  * if moved.
  585                                  */
  586                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  587                                 if (!fs.m) {
  588                                         unlock_and_deallocate(&fs);
  589                                         goto RetryFault;
  590                                 }
  591 
  592                                 hardfault++;
  593                                 break; /* break to PAGE HAS BEEN FOUND */
  594                         }
  595                         /*
  596                          * Remove the bogus page (which does not exist at this
  597                          * object/offset); before doing so, we must get back
  598                          * our object lock to preserve our invariant.
  599                          *
  600                          * Also wake up any other process that may want to bring
  601                          * in this page.
  602                          *
  603                          * If this is the top-level object, we must leave the
  604                          * busy page to prevent another process from rushing
  605                          * past us, and inserting the page in that object at
  606                          * the same time that we are.
  607                          */
  608                         if (rv == VM_PAGER_ERROR)
  609                                 printf("vm_fault: pager read error, pid %d (%s)\n",
  610                                     curproc->p_pid, curproc->p_comm);
  611                         /*
  612                          * Data outside the range of the pager or an I/O error
  613                          */
  614                         /*
  615                          * XXX - the check for kernel_map is a kludge to work
  616                          * around having the machine panic on a kernel space
  617                          * fault w/ I/O error.
  618                          */
  619                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
  620                                 (rv == VM_PAGER_BAD)) {
  621                                 vm_page_lock_queues();
  622                                 vm_page_free(fs.m);
  623                                 vm_page_unlock_queues();
  624                                 fs.m = NULL;
  625                                 unlock_and_deallocate(&fs);
  626                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
  627                         }
  628                         if (fs.object != fs.first_object) {
  629                                 vm_page_lock_queues();
  630                                 vm_page_free(fs.m);
  631                                 vm_page_unlock_queues();
  632                                 fs.m = NULL;
  633                                 /*
  634                                  * XXX - we cannot just fall out at this
  635                                  * point, m has been freed and is invalid!
  636                                  */
  637                         }
  638                 }
  639 
  640                 /*
  641                  * We get here if the object has default pager (or unwiring) 
  642                  * or the pager doesn't have the page.
  643                  */
  644                 if (fs.object == fs.first_object)
  645                         fs.first_m = fs.m;
  646 
  647                 /*
  648                  * Move on to the next object.  Lock the next object before
  649                  * unlocking the current one.
  650                  */
  651                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
  652                 next_object = fs.object->backing_object;
  653                 if (next_object == NULL) {
  654                         /*
  655                          * If there's no object left, fill the page in the top
  656                          * object with zeros.
  657                          */
  658                         if (fs.object != fs.first_object) {
  659                                 vm_object_pip_wakeup(fs.object);
  660                                 VM_OBJECT_UNLOCK(fs.object);
  661 
  662                                 fs.object = fs.first_object;
  663                                 fs.pindex = fs.first_pindex;
  664                                 fs.m = fs.first_m;
  665                                 VM_OBJECT_LOCK(fs.object);
  666                         }
  667                         fs.first_m = NULL;
  668 
  669                         /*
  670                          * Zero the page if necessary and mark it valid.
  671                          */
  672                         if ((fs.m->flags & PG_ZERO) == 0) {
  673                                 pmap_zero_page(fs.m);
  674                         } else {
  675                                 atomic_add_int(&cnt.v_ozfod, 1);
  676                         }
  677                         atomic_add_int(&cnt.v_zfod, 1);
  678                         fs.m->valid = VM_PAGE_BITS_ALL;
  679                         break;  /* break to PAGE HAS BEEN FOUND */
  680                 } else {
  681                         KASSERT(fs.object != next_object,
  682                             ("object loop %p", next_object));
  683                         VM_OBJECT_LOCK(next_object);
  684                         vm_object_pip_add(next_object, 1);
  685                         if (fs.object != fs.first_object)
  686                                 vm_object_pip_wakeup(fs.object);
  687                         VM_OBJECT_UNLOCK(fs.object);
  688                         fs.object = next_object;
  689                 }
  690         }
  691 
  692         KASSERT((fs.m->flags & PG_BUSY) != 0,
  693             ("vm_fault: not busy after main loop"));
  694 
  695         /*
  696          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
  697          * is held.]
  698          */
  699 
  700         /*
  701          * If the page is being written, but isn't already owned by the
  702          * top-level object, we have to copy it into a new page owned by the
  703          * top-level object.
  704          */
  705         if (fs.object != fs.first_object) {
  706                 /*
  707                  * We only really need to copy if we want to write it.
  708                  */
  709                 if (fault_type & VM_PROT_WRITE) {
  710                         /*
  711                          * This allows pages to be virtually copied from a 
  712                          * backing_object into the first_object, where the 
  713                          * backing object has no other refs to it, and cannot
  714                          * gain any more refs.  Instead of a bcopy, we just 
  715                          * move the page from the backing object to the 
  716                          * first object.  Note that we must mark the page 
  717                          * dirty in the first object so that it will go out 
  718                          * to swap when needed.
  719                          */
  720                         is_first_object_locked = FALSE;
  721                         if (
  722                                 /*
  723                                  * Only one shadow object
  724                                  */
  725                                 (fs.object->shadow_count == 1) &&
  726                                 /*
  727                                  * No COW refs, except us
  728                                  */
  729                                 (fs.object->ref_count == 1) &&
  730                                 /*
  731                                  * No one else can look this object up
  732                                  */
  733                                 (fs.object->handle == NULL) &&
  734                                 /*
  735                                  * No other ways to look the object up
  736                                  */
  737                                 ((fs.object->type == OBJT_DEFAULT) ||
  738                                  (fs.object->type == OBJT_SWAP)) &&
  739                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
  740                                 /*
  741                                  * We don't chase down the shadow chain
  742                                  */
  743                             fs.object == fs.first_object->backing_object) {
  744                                 vm_page_lock_queues();
  745                                 /*
  746                                  * get rid of the unnecessary page
  747                                  */
  748                                 pmap_remove_all(fs.first_m);
  749                                 vm_page_free(fs.first_m);
  750                                 /*
  751                                  * grab the page and put it into the 
  752                                  * process'es object.  The page is 
  753                                  * automatically made dirty.
  754                                  */
  755                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
  756                                 vm_page_busy(fs.m);
  757                                 vm_page_unlock_queues();
  758                                 fs.first_m = fs.m;
  759                                 fs.m = NULL;
  760                                 atomic_add_int(&cnt.v_cow_optim, 1);
  761                         } else {
  762                                 /*
  763                                  * Oh, well, lets copy it.
  764                                  */
  765                                 pmap_copy_page(fs.m, fs.first_m);
  766                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
  767                         }
  768                         if (fs.m) {
  769                                 /*
  770                                  * We no longer need the old page or object.
  771                                  */
  772                                 release_page(&fs);
  773                         }
  774                         /*
  775                          * fs.object != fs.first_object due to above 
  776                          * conditional
  777                          */
  778                         vm_object_pip_wakeup(fs.object);
  779                         VM_OBJECT_UNLOCK(fs.object);
  780                         /*
  781                          * Only use the new page below...
  782                          */
  783                         fs.object = fs.first_object;
  784                         fs.pindex = fs.first_pindex;
  785                         fs.m = fs.first_m;
  786                         if (!is_first_object_locked)
  787                                 VM_OBJECT_LOCK(fs.object);
  788                         atomic_add_int(&cnt.v_cow_faults, 1);
  789                 } else {
  790                         prot &= ~VM_PROT_WRITE;
  791                 }
  792         }
  793 
  794         /*
  795          * We must verify that the maps have not changed since our last
  796          * lookup.
  797          */
  798         if (!fs.lookup_still_valid) {
  799                 vm_object_t retry_object;
  800                 vm_pindex_t retry_pindex;
  801                 vm_prot_t retry_prot;
  802 
  803                 if (!vm_map_trylock_read(fs.map)) {
  804                         release_page(&fs);
  805                         unlock_and_deallocate(&fs);
  806                         goto RetryFault;
  807                 }
  808                 fs.lookup_still_valid = TRUE;
  809                 if (fs.map->timestamp != map_generation) {
  810                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
  811                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
  812 
  813                         /*
  814                          * If we don't need the page any longer, put it on the active
  815                          * list (the easiest thing to do here).  If no one needs it,
  816                          * pageout will grab it eventually.
  817                          */
  818                         if (result != KERN_SUCCESS) {
  819                                 release_page(&fs);
  820                                 unlock_and_deallocate(&fs);
  821 
  822                                 /*
  823                                  * If retry of map lookup would have blocked then
  824                                  * retry fault from start.
  825                                  */
  826                                 if (result == KERN_FAILURE)
  827                                         goto RetryFault;
  828                                 return (result);
  829                         }
  830                         if ((retry_object != fs.first_object) ||
  831                             (retry_pindex != fs.first_pindex)) {
  832                                 release_page(&fs);
  833                                 unlock_and_deallocate(&fs);
  834                                 goto RetryFault;
  835                         }
  836 
  837                         /*
  838                          * Check whether the protection has changed or the object has
  839                          * been copied while we left the map unlocked. Changing from
  840                          * read to write permission is OK - we leave the page
  841                          * write-protected, and catch the write fault. Changing from
  842                          * write to read permission means that we can't mark the page
  843                          * write-enabled after all.
  844                          */
  845                         prot &= retry_prot;
  846                 }
  847         }
  848         if (prot & VM_PROT_WRITE) {
  849                 vm_page_lock_queues();
  850                 vm_page_flag_set(fs.m, PG_WRITEABLE);
  851                 vm_object_set_writeable_dirty(fs.m->object);
  852 
  853                 /*
  854                  * If the fault is a write, we know that this page is being
  855                  * written NOW so dirty it explicitly to save on 
  856                  * pmap_is_modified() calls later.
  857                  *
  858                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
  859                  * if the page is already dirty to prevent data written with
  860                  * the expectation of being synced from not being synced.
  861                  * Likewise if this entry does not request NOSYNC then make
  862                  * sure the page isn't marked NOSYNC.  Applications sharing
  863                  * data should use the same flags to avoid ping ponging.
  864                  *
  865                  * Also tell the backing pager, if any, that it should remove
  866                  * any swap backing since the page is now dirty.
  867                  */
  868                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
  869                         if (fs.m->dirty == 0)
  870                                 vm_page_flag_set(fs.m, PG_NOSYNC);
  871                 } else {
  872                         vm_page_flag_clear(fs.m, PG_NOSYNC);
  873                 }
  874                 vm_page_unlock_queues();
  875                 if (fault_flags & VM_FAULT_DIRTY) {
  876                         vm_page_dirty(fs.m);
  877                         vm_pager_page_unswapped(fs.m);
  878                 }
  879         }
  880 
  881         /*
  882          * Page had better still be busy
  883          */
  884         KASSERT(fs.m->flags & PG_BUSY,
  885                 ("vm_fault: page %p not busy!", fs.m));
  886         /*
  887          * Sanity check: page must be completely valid or it is not fit to
  888          * map into user space.  vm_pager_get_pages() ensures this.
  889          */
  890         if (fs.m->valid != VM_PAGE_BITS_ALL) {
  891                 vm_page_zero_invalid(fs.m, TRUE);
  892                 printf("Warning: page %p partially invalid on fault\n", fs.m);
  893         }
  894         VM_OBJECT_UNLOCK(fs.object);
  895 
  896         /*
  897          * Put this page into the physical map.  We had to do the unlock above
  898          * because pmap_enter() may sleep.  We don't put the page
  899          * back on the active queue until later so that the pageout daemon
  900          * won't find it (yet).
  901          */
  902         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
  903         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
  904                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
  905         }
  906         VM_OBJECT_LOCK(fs.object);
  907         vm_page_lock_queues();
  908         vm_page_flag_set(fs.m, PG_REFERENCED);
  909 
  910         /*
  911          * If the page is not wired down, then put it where the pageout daemon
  912          * can find it.
  913          */
  914         if (fault_flags & VM_FAULT_WIRE_MASK) {
  915                 if (wired)
  916                         vm_page_wire(fs.m);
  917                 else
  918                         vm_page_unwire(fs.m, 1);
  919         } else {
  920                 vm_page_activate(fs.m);
  921         }
  922         vm_page_wakeup(fs.m);
  923         vm_page_unlock_queues();
  924 
  925         /*
  926          * Unlock everything, and return
  927          */
  928         unlock_and_deallocate(&fs);
  929         PROC_LOCK(curproc);
  930         if ((curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
  931                 if (hardfault) {
  932                         curproc->p_stats->p_ru.ru_majflt++;
  933                 } else {
  934                         curproc->p_stats->p_ru.ru_minflt++;
  935                 }
  936         }
  937         PROC_UNLOCK(curproc);
  938 
  939         return (KERN_SUCCESS);
  940 }
  941 
  942 /*
  943  * vm_fault_prefault provides a quick way of clustering
  944  * pagefaults into a processes address space.  It is a "cousin"
  945  * of vm_map_pmap_enter, except it runs at page fault time instead
  946  * of mmap time.
  947  */
  948 static void
  949 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
  950 {
  951         int i;
  952         vm_offset_t addr, starta;
  953         vm_pindex_t pindex;
  954         vm_page_t m, mpte;
  955         vm_object_t object;
  956 
  957         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
  958                 return;
  959 
  960         object = entry->object.vm_object;
  961 
  962         starta = addra - PFBAK * PAGE_SIZE;
  963         if (starta < entry->start) {
  964                 starta = entry->start;
  965         } else if (starta > addra) {
  966                 starta = 0;
  967         }
  968 
  969         mpte = NULL;
  970         for (i = 0; i < PAGEORDER_SIZE; i++) {
  971                 vm_object_t backing_object, lobject;
  972 
  973                 addr = addra + prefault_pageorder[i];
  974                 if (addr > addra + (PFFOR * PAGE_SIZE))
  975                         addr = 0;
  976 
  977                 if (addr < starta || addr >= entry->end)
  978                         continue;
  979 
  980                 if (!pmap_is_prefaultable(pmap, addr))
  981                         continue;
  982 
  983                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
  984                 lobject = object;
  985                 VM_OBJECT_LOCK(lobject);
  986                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
  987                     lobject->type == OBJT_DEFAULT &&
  988                     (backing_object = lobject->backing_object) != NULL) {
  989                         if (lobject->backing_object_offset & PAGE_MASK)
  990                                 break;
  991                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
  992                         VM_OBJECT_LOCK(backing_object);
  993                         VM_OBJECT_UNLOCK(lobject);
  994                         lobject = backing_object;
  995                 }
  996                 /*
  997                  * give-up when a page is not in memory
  998                  */
  999                 if (m == NULL) {
 1000                         VM_OBJECT_UNLOCK(lobject);
 1001                         break;
 1002                 }
 1003                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
 1004                         (m->busy == 0) &&
 1005                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
 1006 
 1007                         vm_page_lock_queues();
 1008                         if ((m->queue - m->pc) == PQ_CACHE)
 1009                                 vm_page_deactivate(m);
 1010                         mpte = pmap_enter_quick(pmap, addr, m, mpte);
 1011                         vm_page_unlock_queues();
 1012                 }
 1013                 VM_OBJECT_UNLOCK(lobject);
 1014         }
 1015 }
 1016 
 1017 /*
 1018  *      vm_fault_quick:
 1019  *
 1020  *      Ensure that the requested virtual address, which may be in userland,
 1021  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
 1022  */
 1023 int
 1024 vm_fault_quick(caddr_t v, int prot)
 1025 {
 1026         int r;
 1027 
 1028         if (prot & VM_PROT_WRITE)
 1029                 r = subyte(v, fubyte(v));
 1030         else
 1031                 r = fubyte(v);
 1032         return(r);
 1033 }
 1034 
 1035 /*
 1036  *      vm_fault_wire:
 1037  *
 1038  *      Wire down a range of virtual addresses in a map.
 1039  */
 1040 int
 1041 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1042     boolean_t user_wire, boolean_t fictitious)
 1043 {
 1044         vm_offset_t va;
 1045         int rv;
 1046 
 1047         /*
 1048          * We simulate a fault to get the page and enter it in the physical
 1049          * map.  For user wiring, we only ask for read access on currently
 1050          * read-only sections.
 1051          */
 1052         for (va = start; va < end; va += PAGE_SIZE) {
 1053                 rv = vm_fault(map, va,
 1054                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
 1055                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
 1056                 if (rv) {
 1057                         if (va != start)
 1058                                 vm_fault_unwire(map, start, va, fictitious);
 1059                         return (rv);
 1060                 }
 1061         }
 1062         return (KERN_SUCCESS);
 1063 }
 1064 
 1065 /*
 1066  *      vm_fault_unwire:
 1067  *
 1068  *      Unwire a range of virtual addresses in a map.
 1069  */
 1070 void
 1071 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1072     boolean_t fictitious)
 1073 {
 1074         vm_paddr_t pa;
 1075         vm_offset_t va;
 1076         pmap_t pmap;
 1077 
 1078         pmap = vm_map_pmap(map);
 1079 
 1080         /*
 1081          * Since the pages are wired down, we must be able to get their
 1082          * mappings from the physical map system.
 1083          */
 1084         for (va = start; va < end; va += PAGE_SIZE) {
 1085                 pa = pmap_extract(pmap, va);
 1086                 if (pa != 0) {
 1087                         pmap_change_wiring(pmap, va, FALSE);
 1088                         if (!fictitious) {
 1089                                 vm_page_lock_queues();
 1090                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
 1091                                 vm_page_unlock_queues();
 1092                         }
 1093                 }
 1094         }
 1095 }
 1096 
 1097 /*
 1098  *      Routine:
 1099  *              vm_fault_copy_entry
 1100  *      Function:
 1101  *              Copy all of the pages from a wired-down map entry to another.
 1102  *
 1103  *      In/out conditions:
 1104  *              The source and destination maps must be locked for write.
 1105  *              The source map entry must be wired down (or be a sharing map
 1106  *              entry corresponding to a main map entry that is wired down).
 1107  */
 1108 void
 1109 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
 1110         vm_map_t dst_map;
 1111         vm_map_t src_map;
 1112         vm_map_entry_t dst_entry;
 1113         vm_map_entry_t src_entry;
 1114 {
 1115         vm_object_t backing_object, dst_object, object;
 1116         vm_object_t src_object;
 1117         vm_ooffset_t dst_offset;
 1118         vm_ooffset_t src_offset;
 1119         vm_pindex_t pindex;
 1120         vm_prot_t prot;
 1121         vm_offset_t vaddr;
 1122         vm_page_t dst_m;
 1123         vm_page_t src_m;
 1124 
 1125 #ifdef  lint
 1126         src_map++;
 1127 #endif  /* lint */
 1128 
 1129         src_object = src_entry->object.vm_object;
 1130         src_offset = src_entry->offset;
 1131 
 1132         /*
 1133          * Create the top-level object for the destination entry. (Doesn't
 1134          * actually shadow anything - we copy the pages directly.)
 1135          */
 1136         dst_object = vm_object_allocate(OBJT_DEFAULT,
 1137             OFF_TO_IDX(dst_entry->end - dst_entry->start));
 1138 
 1139         VM_OBJECT_LOCK(dst_object);
 1140         dst_entry->object.vm_object = dst_object;
 1141         dst_entry->offset = 0;
 1142 
 1143         prot = dst_entry->max_protection;
 1144 
 1145         /*
 1146          * Loop through all of the pages in the entry's range, copying each
 1147          * one from the source object (it should be there) to the destination
 1148          * object.
 1149          */
 1150         for (vaddr = dst_entry->start, dst_offset = 0;
 1151             vaddr < dst_entry->end;
 1152             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
 1153 
 1154                 /*
 1155                  * Allocate a page in the destination object
 1156                  */
 1157                 do {
 1158                         dst_m = vm_page_alloc(dst_object,
 1159                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
 1160                         if (dst_m == NULL) {
 1161                                 VM_OBJECT_UNLOCK(dst_object);
 1162                                 VM_WAIT;
 1163                                 VM_OBJECT_LOCK(dst_object);
 1164                         }
 1165                 } while (dst_m == NULL);
 1166 
 1167                 /*
 1168                  * Find the page in the source object, and copy it in.
 1169                  * (Because the source is wired down, the page will be in
 1170                  * memory.)
 1171                  */
 1172                 VM_OBJECT_LOCK(src_object);
 1173                 object = src_object;
 1174                 pindex = 0;
 1175                 while ((src_m = vm_page_lookup(object, pindex +
 1176                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
 1177                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
 1178                     (backing_object = object->backing_object) != NULL) {
 1179                         /*
 1180                          * Allow fallback to backing objects if we are reading.
 1181                          */
 1182                         VM_OBJECT_LOCK(backing_object);
 1183                         pindex += OFF_TO_IDX(object->backing_object_offset);
 1184                         VM_OBJECT_UNLOCK(object);
 1185                         object = backing_object;
 1186                 }
 1187                 if (src_m == NULL)
 1188                         panic("vm_fault_copy_wired: page missing");
 1189                 pmap_copy_page(src_m, dst_m);
 1190                 VM_OBJECT_UNLOCK(object);
 1191                 dst_m->valid = VM_PAGE_BITS_ALL;
 1192                 VM_OBJECT_UNLOCK(dst_object);
 1193 
 1194                 /*
 1195                  * Enter it in the pmap...
 1196                  */
 1197                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
 1198                 VM_OBJECT_LOCK(dst_object);
 1199                 vm_page_lock_queues();
 1200                 if ((prot & VM_PROT_WRITE) != 0)
 1201                         vm_page_flag_set(dst_m, PG_WRITEABLE);
 1202 
 1203                 /*
 1204                  * Mark it no longer busy, and put it on the active list.
 1205                  */
 1206                 vm_page_activate(dst_m);
 1207                 vm_page_wakeup(dst_m);
 1208                 vm_page_unlock_queues();
 1209         }
 1210         VM_OBJECT_UNLOCK(dst_object);
 1211 }
 1212 
 1213 
 1214 /*
 1215  * This routine checks around the requested page for other pages that
 1216  * might be able to be faulted in.  This routine brackets the viable
 1217  * pages for the pages to be paged in.
 1218  *
 1219  * Inputs:
 1220  *      m, rbehind, rahead
 1221  *
 1222  * Outputs:
 1223  *  marray (array of vm_page_t), reqpage (index of requested page)
 1224  *
 1225  * Return value:
 1226  *  number of pages in marray
 1227  *
 1228  * This routine can't block.
 1229  */
 1230 static int
 1231 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
 1232         vm_page_t m;
 1233         int rbehind;
 1234         int rahead;
 1235         vm_page_t *marray;
 1236         int *reqpage;
 1237 {
 1238         int i,j;
 1239         vm_object_t object;
 1240         vm_pindex_t pindex, startpindex, endpindex, tpindex;
 1241         vm_page_t rtm;
 1242         int cbehind, cahead;
 1243 
 1244         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
 1245 
 1246         object = m->object;
 1247         pindex = m->pindex;
 1248 
 1249         /*
 1250          * we don't fault-ahead for device pager
 1251          */
 1252         if (object->type == OBJT_DEVICE) {
 1253                 *reqpage = 0;
 1254                 marray[0] = m;
 1255                 return 1;
 1256         }
 1257 
 1258         /*
 1259          * if the requested page is not available, then give up now
 1260          */
 1261         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
 1262                 return 0;
 1263         }
 1264 
 1265         if ((cbehind == 0) && (cahead == 0)) {
 1266                 *reqpage = 0;
 1267                 marray[0] = m;
 1268                 return 1;
 1269         }
 1270 
 1271         if (rahead > cahead) {
 1272                 rahead = cahead;
 1273         }
 1274 
 1275         if (rbehind > cbehind) {
 1276                 rbehind = cbehind;
 1277         }
 1278 
 1279         /*
 1280          * try to do any readahead that we might have free pages for.
 1281          */
 1282         if ((rahead + rbehind) >
 1283                 ((cnt.v_free_count + cnt.v_cache_count) - cnt.v_free_reserved)) {
 1284                 pagedaemon_wakeup();
 1285                 marray[0] = m;
 1286                 *reqpage = 0;
 1287                 return 1;
 1288         }
 1289 
 1290         /*
 1291          * scan backward for the read behind pages -- in memory 
 1292          */
 1293         if (pindex > 0) {
 1294                 if (rbehind > pindex) {
 1295                         rbehind = pindex;
 1296                         startpindex = 0;
 1297                 } else {
 1298                         startpindex = pindex - rbehind;
 1299                 }
 1300 
 1301                 for (tpindex = pindex - 1; tpindex >= startpindex; tpindex -= 1) {
 1302                         if (vm_page_lookup(object, tpindex)) {
 1303                                 startpindex = tpindex + 1;
 1304                                 break;
 1305                         }
 1306                         if (tpindex == 0)
 1307                                 break;
 1308                 }
 1309 
 1310                 for (i = 0, tpindex = startpindex; tpindex < pindex; i++, tpindex++) {
 1311 
 1312                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
 1313                         if (rtm == NULL) {
 1314                                 vm_page_lock_queues();
 1315                                 for (j = 0; j < i; j++) {
 1316                                         vm_page_free(marray[j]);
 1317                                 }
 1318                                 vm_page_unlock_queues();
 1319                                 marray[0] = m;
 1320                                 *reqpage = 0;
 1321                                 return 1;
 1322                         }
 1323 
 1324                         marray[i] = rtm;
 1325                 }
 1326         } else {
 1327                 startpindex = 0;
 1328                 i = 0;
 1329         }
 1330 
 1331         marray[i] = m;
 1332         /* page offset of the required page */
 1333         *reqpage = i;
 1334 
 1335         tpindex = pindex + 1;
 1336         i++;
 1337 
 1338         /*
 1339          * scan forward for the read ahead pages
 1340          */
 1341         endpindex = tpindex + rahead;
 1342         if (endpindex > object->size)
 1343                 endpindex = object->size;
 1344 
 1345         for (; tpindex < endpindex; i++, tpindex++) {
 1346 
 1347                 if (vm_page_lookup(object, tpindex)) {
 1348                         break;
 1349                 }
 1350 
 1351                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
 1352                 if (rtm == NULL) {
 1353                         break;
 1354                 }
 1355 
 1356                 marray[i] = rtm;
 1357         }
 1358 
 1359         /* return number of bytes of pages */
 1360         return i;
 1361 }

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