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/6.4/sys/vm/vm_fault.c 173367 2007-11-05 16:18:00Z ups $");
   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         boolean_t firstobjneedgiant;
  156 
  157         vm_object_pip_wakeup(fs->object);
  158         VM_OBJECT_UNLOCK(fs->object);
  159         if (fs->object != fs->first_object) {
  160                 VM_OBJECT_LOCK(fs->first_object);
  161                 vm_page_lock_queues();
  162                 vm_page_free(fs->first_m);
  163                 vm_page_unlock_queues();
  164                 vm_object_pip_wakeup(fs->first_object);
  165                 VM_OBJECT_UNLOCK(fs->first_object);
  166                 fs->first_m = NULL;
  167         }
  168         firstobjneedgiant = (fs->first_object->flags & OBJ_NEEDGIANT) != 0;
  169         vm_object_deallocate(fs->first_object);
  170         unlock_map(fs); 
  171         if (fs->vp != NULL) { 
  172                 int vfslocked;
  173 
  174                 vfslocked = VFS_LOCK_GIANT(fs->vp->v_mount);
  175                 vput(fs->vp);
  176                 fs->vp = NULL;
  177                 VFS_UNLOCK_GIANT(vfslocked);
  178         }
  179         if (firstobjneedgiant)
  180                 VM_UNLOCK_GIANT();
  181 }
  182 
  183 /*
  184  * TRYPAGER - used by vm_fault to calculate whether the pager for the
  185  *            current object *might* contain the page.
  186  *
  187  *            default objects are zero-fill, there is no real pager.
  188  */
  189 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
  190                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
  191 
  192 /*
  193  *      vm_fault:
  194  *
  195  *      Handle a page fault occurring at the given address,
  196  *      requiring the given permissions, in the map specified.
  197  *      If successful, the page is inserted into the
  198  *      associated physical map.
  199  *
  200  *      NOTE: the given address should be truncated to the
  201  *      proper page address.
  202  *
  203  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
  204  *      a standard error specifying why the fault is fatal is returned.
  205  *
  206  *
  207  *      The map in question must be referenced, and remains so.
  208  *      Caller may hold no locks.
  209  */
  210 int
  211 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
  212          int fault_flags)
  213 {
  214         vm_prot_t prot;
  215         int is_first_object_locked, result;
  216         boolean_t growstack, wired;
  217         int map_generation;
  218         vm_object_t next_object;
  219         vm_page_t marray[VM_FAULT_READ];
  220         int hardfault;
  221         int faultcount;
  222         struct faultstate fs;
  223 
  224         hardfault = 0;
  225         growstack = TRUE;
  226         atomic_add_int(&cnt.v_vm_faults, 1);
  227 
  228 RetryFault:;
  229 
  230         /*
  231          * Find the backing store object and offset into it to begin the
  232          * search.
  233          */
  234         fs.map = map;
  235         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
  236             &fs.first_object, &fs.first_pindex, &prot, &wired);
  237         if (result != KERN_SUCCESS) {
  238                 if (result != KERN_PROTECTION_FAILURE ||
  239                     (fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE) {
  240                         if (growstack && result == KERN_INVALID_ADDRESS &&
  241                             map != kernel_map && curproc != NULL) {
  242                                 result = vm_map_growstack(curproc, vaddr);
  243                                 if (result != KERN_SUCCESS)
  244                                         return (KERN_FAILURE);
  245                                 growstack = FALSE;
  246                                 goto RetryFault;
  247                         }
  248                         return (result);
  249                 }
  250 
  251                 /*
  252                  * If we are user-wiring a r/w segment, and it is COW, then
  253                  * we need to do the COW operation.  Note that we don't COW
  254                  * currently RO sections now, because it is NOT desirable
  255                  * to COW .text.  We simply keep .text from ever being COW'ed
  256                  * and take the heat that one cannot debug wired .text sections.
  257                  */
  258                 result = vm_map_lookup(&fs.map, vaddr,
  259                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
  260                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
  261                 if (result != KERN_SUCCESS)
  262                         return (result);
  263 
  264                 /*
  265                  * If we don't COW now, on a user wire, the user will never
  266                  * be able to write to the mapping.  If we don't make this
  267                  * restriction, the bookkeeping would be nearly impossible.
  268                  *
  269                  * XXX The following assignment modifies the map without
  270                  * holding a write lock on it.
  271                  */
  272                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
  273                         fs.entry->max_protection &= ~VM_PROT_WRITE;
  274         }
  275 
  276         map_generation = fs.map->timestamp;
  277 
  278         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
  279                 panic("vm_fault: fault on nofault entry, addr: %lx",
  280                     (u_long)vaddr);
  281         }
  282 
  283         /*
  284          * Make a reference to this object to prevent its disposal while we
  285          * are messing with it.  Once we have the reference, the map is free
  286          * to be diddled.  Since objects reference their shadows (and copies),
  287          * they will stay around as well.
  288          *
  289          * Bump the paging-in-progress count to prevent size changes (e.g. 
  290          * truncation operations) during I/O.  This must be done after
  291          * obtaining the vnode lock in order to avoid possible deadlocks.
  292          *
  293          * XXX vnode_pager_lock() can block without releasing the map lock.
  294          */
  295         if (fs.first_object->flags & OBJ_NEEDGIANT)
  296                 mtx_lock(&Giant);
  297         VM_OBJECT_LOCK(fs.first_object);
  298         vm_object_reference_locked(fs.first_object);
  299         fs.vp = vnode_pager_lock(fs.first_object);
  300         KASSERT(fs.vp == NULL || !fs.map->system_map,
  301             ("vm_fault: vnode-backed object mapped by system map"));
  302         KASSERT((fs.first_object->flags & OBJ_NEEDGIANT) == 0 ||
  303             !fs.map->system_map,
  304             ("vm_fault: Object requiring giant mapped by system map"));
  305         if (fs.first_object->flags & OBJ_NEEDGIANT && debug_mpsafevm)
  306                 mtx_unlock(&Giant);
  307         vm_object_pip_add(fs.first_object, 1);
  308 
  309         fs.lookup_still_valid = TRUE;
  310 
  311         if (wired)
  312                 fault_type = prot;
  313 
  314         fs.first_m = NULL;
  315 
  316         /*
  317          * Search for the page at object/offset.
  318          */
  319         fs.object = fs.first_object;
  320         fs.pindex = fs.first_pindex;
  321         while (TRUE) {
  322                 /*
  323                  * If the object is dead, we stop here
  324                  */
  325                 if (fs.object->flags & OBJ_DEAD) {
  326                         unlock_and_deallocate(&fs);
  327                         return (KERN_PROTECTION_FAILURE);
  328                 }
  329 
  330                 /*
  331                  * See if page is resident
  332                  */
  333                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  334                 if (fs.m != NULL) {
  335                         int queue;
  336 
  337                         /* 
  338                          * check for page-based copy on write.
  339                          * We check fs.object == fs.first_object so
  340                          * as to ensure the legacy COW mechanism is
  341                          * used when the page in question is part of
  342                          * a shadow object.  Otherwise, vm_page_cowfault()
  343                          * removes the page from the backing object, 
  344                          * which is not what we want.
  345                          */
  346                         vm_page_lock_queues();
  347                         if ((fs.m->cow) && 
  348                             (fault_type & VM_PROT_WRITE) &&
  349                             (fs.object == fs.first_object)) {
  350                                 vm_page_cowfault(fs.m);
  351                                 vm_page_unlock_queues();
  352                                 unlock_and_deallocate(&fs);
  353                                 goto RetryFault;
  354                         }
  355 
  356                         /*
  357                          * Wait/Retry if the page is busy.  We have to do this
  358                          * if the page is busy via either PG_BUSY or 
  359                          * vm_page_t->busy because the vm_pager may be using
  360                          * vm_page_t->busy for pageouts ( and even pageins if
  361                          * it is the vnode pager ), and we could end up trying
  362                          * to pagein and pageout the same page simultaneously.
  363                          *
  364                          * We can theoretically allow the busy case on a read
  365                          * fault if the page is marked valid, but since such
  366                          * pages are typically already pmap'd, putting that
  367                          * special case in might be more effort then it is 
  368                          * worth.  We cannot under any circumstances mess
  369                          * around with a vm_page_t->busy page except, perhaps,
  370                          * to pmap it.
  371                          */
  372                         if ((fs.m->flags & PG_BUSY) || fs.m->busy) {
  373                                 vm_page_unlock_queues();
  374                                 VM_OBJECT_UNLOCK(fs.object);
  375                                 if (fs.object != fs.first_object) {
  376                                         VM_OBJECT_LOCK(fs.first_object);
  377                                         vm_page_lock_queues();
  378                                         vm_page_free(fs.first_m);
  379                                         vm_page_unlock_queues();
  380                                         vm_object_pip_wakeup(fs.first_object);
  381                                         VM_OBJECT_UNLOCK(fs.first_object);
  382                                         fs.first_m = NULL;
  383                                 }
  384                                 unlock_map(&fs);
  385                                 if (fs.vp != NULL) {
  386                                         int vfslck;
  387 
  388                                         vfslck = VFS_LOCK_GIANT(fs.vp->v_mount);
  389                                         vput(fs.vp);
  390                                         fs.vp = NULL;
  391                                         VFS_UNLOCK_GIANT(vfslck);
  392                                 }
  393                                 VM_OBJECT_LOCK(fs.object);
  394                                 if (fs.m == vm_page_lookup(fs.object,
  395                                     fs.pindex)) {
  396                                         vm_page_lock_queues();
  397                                         if (!vm_page_sleep_if_busy(fs.m, TRUE,
  398                                             "vmpfw"))
  399                                                 vm_page_unlock_queues();
  400                                 }
  401                                 vm_object_pip_wakeup(fs.object);
  402                                 VM_OBJECT_UNLOCK(fs.object);
  403                                 atomic_add_int(&cnt.v_intrans, 1);
  404                                 if (fs.first_object->flags & OBJ_NEEDGIANT)
  405                                         VM_UNLOCK_GIANT();
  406                                 vm_object_deallocate(fs.first_object);
  407                                 goto RetryFault;
  408                         }
  409                         queue = fs.m->queue;
  410 
  411                         vm_pageq_remove_nowakeup(fs.m);
  412 
  413                         if ((queue - fs.m->pc) == PQ_CACHE) {
  414                                 cnt.v_reactivated++;
  415                                 if (vm_page_count_severe()) {
  416                                         vm_page_activate(fs.m);
  417                                         vm_page_unlock_queues();
  418                                         unlock_and_deallocate(&fs);
  419                                         VM_WAITPFAULT;
  420                                         goto RetryFault;
  421                                 }
  422                         }
  423 
  424                         /*
  425                          * Mark page busy for other processes, and the 
  426                          * pagedaemon.  If it still isn't completely valid
  427                          * (readable), jump to readrest, else break-out ( we
  428                          * found the page ).
  429                          */
  430                         vm_page_busy(fs.m);
  431                         vm_page_unlock_queues();
  432                         if (((fs.m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) &&
  433                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
  434                                 goto readrest;
  435                         }
  436 
  437                         break;
  438                 }
  439 
  440                 /*
  441                  * Page is not resident, If this is the search termination
  442                  * or the pager might contain the page, allocate a new page.
  443                  */
  444                 if (TRYPAGER || fs.object == fs.first_object) {
  445                         if (fs.pindex >= fs.object->size) {
  446                                 unlock_and_deallocate(&fs);
  447                                 return (KERN_PROTECTION_FAILURE);
  448                         }
  449 
  450                         /*
  451                          * Allocate a new page for this object/offset pair.
  452                          */
  453                         fs.m = NULL;
  454                         if (!vm_page_count_severe()) {
  455                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
  456                                     (fs.vp || fs.object->backing_object)? VM_ALLOC_NORMAL: VM_ALLOC_ZERO);
  457                         }
  458                         if (fs.m == NULL) {
  459                                 unlock_and_deallocate(&fs);
  460                                 VM_WAITPFAULT;
  461                                 goto RetryFault;
  462                         }
  463                 }
  464 
  465 readrest:
  466                 /*
  467                  * We have found a valid page or we have allocated a new page.
  468                  * The page thus may not be valid or may not be entirely 
  469                  * valid.
  470                  *
  471                  * Attempt to fault-in the page if there is a chance that the
  472                  * pager has it, and potentially fault in additional pages
  473                  * at the same time.
  474                  */
  475                 if (TRYPAGER) {
  476                         int rv;
  477                         int reqpage;
  478                         int ahead, behind;
  479                         u_char behavior = vm_map_entry_behavior(fs.entry);
  480 
  481                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
  482                                 ahead = 0;
  483                                 behind = 0;
  484                         } else {
  485                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
  486                                 if (behind > VM_FAULT_READ_BEHIND)
  487                                         behind = VM_FAULT_READ_BEHIND;
  488 
  489                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
  490                                 if (ahead > VM_FAULT_READ_AHEAD)
  491                                         ahead = VM_FAULT_READ_AHEAD;
  492                         }
  493                         is_first_object_locked = FALSE;
  494                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
  495                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
  496                               fs.pindex >= fs.entry->lastr &&
  497                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
  498                             (fs.first_object == fs.object ||
  499                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
  500                             fs.first_object->type != OBJT_DEVICE) {
  501                                 vm_pindex_t firstpindex, tmppindex;
  502 
  503                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
  504                                         firstpindex = 0;
  505                                 else
  506                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
  507 
  508                                 vm_page_lock_queues();
  509                                 /*
  510                                  * note: partially valid pages cannot be 
  511                                  * included in the lookahead - NFS piecemeal
  512                                  * writes will barf on it badly.
  513                                  */
  514                                 for (tmppindex = fs.first_pindex - 1;
  515                                         tmppindex >= firstpindex;
  516                                         --tmppindex) {
  517                                         vm_page_t mt;
  518 
  519                                         mt = vm_page_lookup(fs.first_object, tmppindex);
  520                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
  521                                                 break;
  522                                         if (mt->busy ||
  523                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
  524                                                 mt->hold_count ||
  525                                                 mt->wire_count) 
  526                                                 continue;
  527                                         pmap_remove_all(mt);
  528                                         if (mt->dirty) {
  529                                                 vm_page_deactivate(mt);
  530                                         } else {
  531                                                 vm_page_cache(mt);
  532                                         }
  533                                 }
  534                                 vm_page_unlock_queues();
  535                                 ahead += behind;
  536                                 behind = 0;
  537                         }
  538                         if (is_first_object_locked)
  539                                 VM_OBJECT_UNLOCK(fs.first_object);
  540                         /*
  541                          * now we find out if any other pages should be paged
  542                          * in at this time this routine checks to see if the
  543                          * pages surrounding this fault reside in the same
  544                          * object as the page for this fault.  If they do,
  545                          * then they are faulted in also into the object.  The
  546                          * array "marray" returned contains an array of
  547                          * vm_page_t structs where one of them is the
  548                          * vm_page_t passed to the routine.  The reqpage
  549                          * return value is the index into the marray for the
  550                          * vm_page_t passed to the routine.
  551                          *
  552                          * fs.m plus the additional pages are PG_BUSY'd.
  553                          *
  554                          * XXX vm_fault_additional_pages() can block
  555                          * without releasing the map lock.
  556                          */
  557                         faultcount = vm_fault_additional_pages(
  558                             fs.m, behind, ahead, marray, &reqpage);
  559 
  560                         /*
  561                          * update lastr imperfectly (we do not know how much
  562                          * getpages will actually read), but good enough.
  563                          *
  564                          * XXX The following assignment modifies the map
  565                          * without holding a write lock on it.
  566                          */
  567                         fs.entry->lastr = fs.pindex + faultcount - behind;
  568 
  569                         /*
  570                          * Call the pager to retrieve the data, if any, after
  571                          * releasing the lock on the map.  We hold a ref on
  572                          * fs.object and the pages are PG_BUSY'd.
  573                          */
  574                         unlock_map(&fs);
  575 
  576                         rv = faultcount ?
  577                             vm_pager_get_pages(fs.object, marray, faultcount,
  578                                 reqpage) : VM_PAGER_FAIL;
  579 
  580                         if (rv == VM_PAGER_OK) {
  581                                 /*
  582                                  * Found the page. Leave it busy while we play
  583                                  * with it.
  584                                  */
  585 
  586                                 /*
  587                                  * Relookup in case pager changed page. Pager
  588                                  * is responsible for disposition of old page
  589                                  * if moved.
  590                                  */
  591                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  592                                 if (!fs.m) {
  593                                         unlock_and_deallocate(&fs);
  594                                         goto RetryFault;
  595                                 }
  596 
  597                                 hardfault++;
  598                                 break; /* break to PAGE HAS BEEN FOUND */
  599                         }
  600                         /*
  601                          * Remove the bogus page (which does not exist at this
  602                          * object/offset); before doing so, we must get back
  603                          * our object lock to preserve our invariant.
  604                          *
  605                          * Also wake up any other process that may want to bring
  606                          * in this page.
  607                          *
  608                          * If this is the top-level object, we must leave the
  609                          * busy page to prevent another process from rushing
  610                          * past us, and inserting the page in that object at
  611                          * the same time that we are.
  612                          */
  613                         if (rv == VM_PAGER_ERROR)
  614                                 printf("vm_fault: pager read error, pid %d (%s)\n",
  615                                     curproc->p_pid, curproc->p_comm);
  616                         /*
  617                          * Data outside the range of the pager or an I/O error
  618                          */
  619                         /*
  620                          * XXX - the check for kernel_map is a kludge to work
  621                          * around having the machine panic on a kernel space
  622                          * fault w/ I/O error.
  623                          */
  624                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
  625                                 (rv == VM_PAGER_BAD)) {
  626                                 vm_page_lock_queues();
  627                                 vm_page_free(fs.m);
  628                                 vm_page_unlock_queues();
  629                                 fs.m = NULL;
  630                                 unlock_and_deallocate(&fs);
  631                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
  632                         }
  633                         if (fs.object != fs.first_object) {
  634                                 vm_page_lock_queues();
  635                                 vm_page_free(fs.m);
  636                                 vm_page_unlock_queues();
  637                                 fs.m = NULL;
  638                                 /*
  639                                  * XXX - we cannot just fall out at this
  640                                  * point, m has been freed and is invalid!
  641                                  */
  642                         }
  643                 }
  644 
  645                 /*
  646                  * We get here if the object has default pager (or unwiring) 
  647                  * or the pager doesn't have the page.
  648                  */
  649                 if (fs.object == fs.first_object)
  650                         fs.first_m = fs.m;
  651 
  652                 /*
  653                  * Move on to the next object.  Lock the next object before
  654                  * unlocking the current one.
  655                  */
  656                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
  657                 next_object = fs.object->backing_object;
  658                 if (next_object == NULL) {
  659                         /*
  660                          * If there's no object left, fill the page in the top
  661                          * object with zeros.
  662                          */
  663                         if (fs.object != fs.first_object) {
  664                                 vm_object_pip_wakeup(fs.object);
  665                                 VM_OBJECT_UNLOCK(fs.object);
  666 
  667                                 fs.object = fs.first_object;
  668                                 fs.pindex = fs.first_pindex;
  669                                 fs.m = fs.first_m;
  670                                 VM_OBJECT_LOCK(fs.object);
  671                         }
  672                         fs.first_m = NULL;
  673 
  674                         /*
  675                          * Zero the page if necessary and mark it valid.
  676                          */
  677                         if ((fs.m->flags & PG_ZERO) == 0) {
  678                                 pmap_zero_page(fs.m);
  679                         } else {
  680                                 atomic_add_int(&cnt.v_ozfod, 1);
  681                         }
  682                         atomic_add_int(&cnt.v_zfod, 1);
  683                         fs.m->valid = VM_PAGE_BITS_ALL;
  684                         break;  /* break to PAGE HAS BEEN FOUND */
  685                 } else {
  686                         KASSERT(fs.object != next_object,
  687                             ("object loop %p", next_object));
  688                         VM_OBJECT_LOCK(next_object);
  689                         vm_object_pip_add(next_object, 1);
  690                         if (fs.object != fs.first_object)
  691                                 vm_object_pip_wakeup(fs.object);
  692                         VM_OBJECT_UNLOCK(fs.object);
  693                         fs.object = next_object;
  694                 }
  695         }
  696 
  697         KASSERT((fs.m->flags & PG_BUSY) != 0,
  698             ("vm_fault: not busy after main loop"));
  699 
  700         /*
  701          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
  702          * is held.]
  703          */
  704 
  705         /*
  706          * If the page is being written, but isn't already owned by the
  707          * top-level object, we have to copy it into a new page owned by the
  708          * top-level object.
  709          */
  710         if (fs.object != fs.first_object) {
  711                 /*
  712                  * We only really need to copy if we want to write it.
  713                  */
  714                 if (fault_type & VM_PROT_WRITE) {
  715                         /*
  716                          * This allows pages to be virtually copied from a 
  717                          * backing_object into the first_object, where the 
  718                          * backing object has no other refs to it, and cannot
  719                          * gain any more refs.  Instead of a bcopy, we just 
  720                          * move the page from the backing object to the 
  721                          * first object.  Note that we must mark the page 
  722                          * dirty in the first object so that it will go out 
  723                          * to swap when needed.
  724                          */
  725                         is_first_object_locked = FALSE;
  726                         if (
  727                                 /*
  728                                  * Only one shadow object
  729                                  */
  730                                 (fs.object->shadow_count == 1) &&
  731                                 /*
  732                                  * No COW refs, except us
  733                                  */
  734                                 (fs.object->ref_count == 1) &&
  735                                 /*
  736                                  * No one else can look this object up
  737                                  */
  738                                 (fs.object->handle == NULL) &&
  739                                 /*
  740                                  * No other ways to look the object up
  741                                  */
  742                                 ((fs.object->type == OBJT_DEFAULT) ||
  743                                  (fs.object->type == OBJT_SWAP)) &&
  744                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
  745                                 /*
  746                                  * We don't chase down the shadow chain
  747                                  */
  748                             fs.object == fs.first_object->backing_object) {
  749                                 vm_page_lock_queues();
  750                                 /*
  751                                  * get rid of the unnecessary page
  752                                  */
  753                                 pmap_remove_all(fs.first_m);
  754                                 vm_page_free(fs.first_m);
  755                                 /*
  756                                  * grab the page and put it into the 
  757                                  * process'es object.  The page is 
  758                                  * automatically made dirty.
  759                                  */
  760                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
  761                                 vm_page_busy(fs.m);
  762                                 vm_page_unlock_queues();
  763                                 fs.first_m = fs.m;
  764                                 fs.m = NULL;
  765                                 atomic_add_int(&cnt.v_cow_optim, 1);
  766                         } else {
  767                                 /*
  768                                  * Oh, well, lets copy it.
  769                                  */
  770                                 pmap_copy_page(fs.m, fs.first_m);
  771                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
  772                         }
  773                         if (fs.m) {
  774                                 /*
  775                                  * We no longer need the old page or object.
  776                                  */
  777                                 release_page(&fs);
  778                         }
  779                         /*
  780                          * fs.object != fs.first_object due to above 
  781                          * conditional
  782                          */
  783                         vm_object_pip_wakeup(fs.object);
  784                         VM_OBJECT_UNLOCK(fs.object);
  785                         /*
  786                          * Only use the new page below...
  787                          */
  788                         fs.object = fs.first_object;
  789                         fs.pindex = fs.first_pindex;
  790                         fs.m = fs.first_m;
  791                         if (!is_first_object_locked)
  792                                 VM_OBJECT_LOCK(fs.object);
  793                         atomic_add_int(&cnt.v_cow_faults, 1);
  794                 } else {
  795                         prot &= ~VM_PROT_WRITE;
  796                 }
  797         }
  798 
  799         /*
  800          * We must verify that the maps have not changed since our last
  801          * lookup.
  802          */
  803         if (!fs.lookup_still_valid) {
  804                 vm_object_t retry_object;
  805                 vm_pindex_t retry_pindex;
  806                 vm_prot_t retry_prot;
  807 
  808                 if (!vm_map_trylock_read(fs.map)) {
  809                         release_page(&fs);
  810                         unlock_and_deallocate(&fs);
  811                         goto RetryFault;
  812                 }
  813                 fs.lookup_still_valid = TRUE;
  814                 if (fs.map->timestamp != map_generation) {
  815                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
  816                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
  817 
  818                         /*
  819                          * If we don't need the page any longer, put it on the inactive
  820                          * list (the easiest thing to do here).  If no one needs it,
  821                          * pageout will grab it eventually.
  822                          */
  823                         if (result != KERN_SUCCESS) {
  824                                 release_page(&fs);
  825                                 unlock_and_deallocate(&fs);
  826 
  827                                 /*
  828                                  * If retry of map lookup would have blocked then
  829                                  * retry fault from start.
  830                                  */
  831                                 if (result == KERN_FAILURE)
  832                                         goto RetryFault;
  833                                 return (result);
  834                         }
  835                         if ((retry_object != fs.first_object) ||
  836                             (retry_pindex != fs.first_pindex)) {
  837                                 release_page(&fs);
  838                                 unlock_and_deallocate(&fs);
  839                                 goto RetryFault;
  840                         }
  841 
  842                         /*
  843                          * Check whether the protection has changed or the object has
  844                          * been copied while we left the map unlocked. Changing from
  845                          * read to write permission is OK - we leave the page
  846                          * write-protected, and catch the write fault. Changing from
  847                          * write to read permission means that we can't mark the page
  848                          * write-enabled after all.
  849                          */
  850                         prot &= retry_prot;
  851                 }
  852         }
  853         if (prot & VM_PROT_WRITE) {
  854                 vm_page_lock_queues();
  855                 vm_page_flag_set(fs.m, PG_WRITEABLE);
  856                 vm_object_set_writeable_dirty(fs.m->object);
  857 
  858                 /*
  859                  * If the fault is a write, we know that this page is being
  860                  * written NOW so dirty it explicitly to save on 
  861                  * pmap_is_modified() calls later.
  862                  *
  863                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
  864                  * if the page is already dirty to prevent data written with
  865                  * the expectation of being synced from not being synced.
  866                  * Likewise if this entry does not request NOSYNC then make
  867                  * sure the page isn't marked NOSYNC.  Applications sharing
  868                  * data should use the same flags to avoid ping ponging.
  869                  *
  870                  * Also tell the backing pager, if any, that it should remove
  871                  * any swap backing since the page is now dirty.
  872                  */
  873                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
  874                         if (fs.m->dirty == 0)
  875                                 vm_page_flag_set(fs.m, PG_NOSYNC);
  876                 } else {
  877                         vm_page_flag_clear(fs.m, PG_NOSYNC);
  878                 }
  879                 vm_page_unlock_queues();
  880                 if (fault_flags & VM_FAULT_DIRTY) {
  881                         vm_page_dirty(fs.m);
  882                         vm_pager_page_unswapped(fs.m);
  883                 }
  884         }
  885 
  886         /*
  887          * Page had better still be busy
  888          */
  889         KASSERT(fs.m->flags & PG_BUSY,
  890                 ("vm_fault: page %p not busy!", fs.m));
  891         /*
  892          * Sanity check: page must be completely valid or it is not fit to
  893          * map into user space.  vm_pager_get_pages() ensures this.
  894          */
  895         if (fs.m->valid != VM_PAGE_BITS_ALL) {
  896                 vm_page_zero_invalid(fs.m, TRUE);
  897                 printf("Warning: page %p partially invalid on fault\n", fs.m);
  898         }
  899         VM_OBJECT_UNLOCK(fs.object);
  900 
  901         /*
  902          * Put this page into the physical map.  We had to do the unlock above
  903          * because pmap_enter() may sleep.  We don't put the page
  904          * back on the active queue until later so that the pageout daemon
  905          * won't find it (yet).
  906          */
  907         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
  908         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
  909                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
  910         }
  911         VM_OBJECT_LOCK(fs.object);
  912         vm_page_lock_queues();
  913         vm_page_flag_set(fs.m, PG_REFERENCED);
  914 
  915         /*
  916          * If the page is not wired down, then put it where the pageout daemon
  917          * can find it.
  918          */
  919         if (fault_flags & VM_FAULT_WIRE_MASK) {
  920                 if (wired)
  921                         vm_page_wire(fs.m);
  922                 else
  923                         vm_page_unwire(fs.m, 1);
  924         } else {
  925                 vm_page_activate(fs.m);
  926         }
  927         vm_page_wakeup(fs.m);
  928         vm_page_unlock_queues();
  929 
  930         /*
  931          * Unlock everything, and return
  932          */
  933         unlock_and_deallocate(&fs);
  934         PROC_LOCK(curproc);
  935         if ((curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
  936                 if (hardfault) {
  937                         curproc->p_stats->p_ru.ru_majflt++;
  938                 } else {
  939                         curproc->p_stats->p_ru.ru_minflt++;
  940                 }
  941         }
  942         PROC_UNLOCK(curproc);
  943 
  944         return (KERN_SUCCESS);
  945 }
  946 
  947 /*
  948  * vm_fault_prefault provides a quick way of clustering
  949  * pagefaults into a processes address space.  It is a "cousin"
  950  * of vm_map_pmap_enter, except it runs at page fault time instead
  951  * of mmap time.
  952  */
  953 static void
  954 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
  955 {
  956         int i;
  957         vm_offset_t addr, starta;
  958         vm_pindex_t pindex;
  959         vm_page_t m;
  960         vm_object_t object;
  961 
  962         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
  963                 return;
  964 
  965         object = entry->object.vm_object;
  966 
  967         starta = addra - PFBAK * PAGE_SIZE;
  968         if (starta < entry->start) {
  969                 starta = entry->start;
  970         } else if (starta > addra) {
  971                 starta = 0;
  972         }
  973 
  974         for (i = 0; i < PAGEORDER_SIZE; i++) {
  975                 vm_object_t backing_object, lobject;
  976 
  977                 addr = addra + prefault_pageorder[i];
  978                 if (addr > addra + (PFFOR * PAGE_SIZE))
  979                         addr = 0;
  980 
  981                 if (addr < starta || addr >= entry->end)
  982                         continue;
  983 
  984                 if (!pmap_is_prefaultable(pmap, addr))
  985                         continue;
  986 
  987                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
  988                 lobject = object;
  989                 VM_OBJECT_LOCK(lobject);
  990                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
  991                     lobject->type == OBJT_DEFAULT &&
  992                     (backing_object = lobject->backing_object) != NULL) {
  993                         if (lobject->backing_object_offset & PAGE_MASK)
  994                                 break;
  995                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
  996                         VM_OBJECT_LOCK(backing_object);
  997                         VM_OBJECT_UNLOCK(lobject);
  998                         lobject = backing_object;
  999                 }
 1000                 /*
 1001                  * give-up when a page is not in memory
 1002                  */
 1003                 if (m == NULL) {
 1004                         VM_OBJECT_UNLOCK(lobject);
 1005                         break;
 1006                 }
 1007                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
 1008                         (m->busy == 0) &&
 1009                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
 1010 
 1011                         vm_page_lock_queues();
 1012                         if ((m->queue - m->pc) == PQ_CACHE)
 1013                                 vm_page_deactivate(m);
 1014                         pmap_enter_quick(pmap, addr, m, entry->protection);
 1015                         vm_page_unlock_queues();
 1016                 }
 1017                 VM_OBJECT_UNLOCK(lobject);
 1018         }
 1019 }
 1020 
 1021 /*
 1022  *      vm_fault_quick:
 1023  *
 1024  *      Ensure that the requested virtual address, which may be in userland,
 1025  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
 1026  */
 1027 int
 1028 vm_fault_quick(caddr_t v, int prot)
 1029 {
 1030         int r;
 1031 
 1032         if (prot & VM_PROT_WRITE)
 1033                 r = subyte(v, fubyte(v));
 1034         else
 1035                 r = fubyte(v);
 1036         return(r);
 1037 }
 1038 
 1039 /*
 1040  *      vm_fault_wire:
 1041  *
 1042  *      Wire down a range of virtual addresses in a map.
 1043  */
 1044 int
 1045 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1046     boolean_t user_wire, boolean_t fictitious)
 1047 {
 1048         vm_offset_t va;
 1049         int rv;
 1050 
 1051         /*
 1052          * We simulate a fault to get the page and enter it in the physical
 1053          * map.  For user wiring, we only ask for read access on currently
 1054          * read-only sections.
 1055          */
 1056         for (va = start; va < end; va += PAGE_SIZE) {
 1057                 rv = vm_fault(map, va,
 1058                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
 1059                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
 1060                 if (rv) {
 1061                         if (va != start)
 1062                                 vm_fault_unwire(map, start, va, fictitious);
 1063                         return (rv);
 1064                 }
 1065         }
 1066         return (KERN_SUCCESS);
 1067 }
 1068 
 1069 /*
 1070  *      vm_fault_unwire:
 1071  *
 1072  *      Unwire a range of virtual addresses in a map.
 1073  */
 1074 void
 1075 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1076     boolean_t fictitious)
 1077 {
 1078         vm_paddr_t pa;
 1079         vm_offset_t va;
 1080         pmap_t pmap;
 1081 
 1082         pmap = vm_map_pmap(map);
 1083 
 1084         /*
 1085          * Since the pages are wired down, we must be able to get their
 1086          * mappings from the physical map system.
 1087          */
 1088         for (va = start; va < end; va += PAGE_SIZE) {
 1089                 pa = pmap_extract(pmap, va);
 1090                 if (pa != 0) {
 1091                         pmap_change_wiring(pmap, va, FALSE);
 1092                         if (!fictitious) {
 1093                                 vm_page_lock_queues();
 1094                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
 1095                                 vm_page_unlock_queues();
 1096                         }
 1097                 }
 1098         }
 1099 }
 1100 
 1101 /*
 1102  *      Routine:
 1103  *              vm_fault_copy_entry
 1104  *      Function:
 1105  *              Copy all of the pages from a wired-down map entry to another.
 1106  *
 1107  *      In/out conditions:
 1108  *              The source and destination maps must be locked for write.
 1109  *              The source map entry must be wired down (or be a sharing map
 1110  *              entry corresponding to a main map entry that is wired down).
 1111  */
 1112 void
 1113 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
 1114         vm_map_t dst_map;
 1115         vm_map_t src_map;
 1116         vm_map_entry_t dst_entry;
 1117         vm_map_entry_t src_entry;
 1118 {
 1119         vm_object_t backing_object, dst_object, object;
 1120         vm_object_t src_object;
 1121         vm_ooffset_t dst_offset;
 1122         vm_ooffset_t src_offset;
 1123         vm_pindex_t pindex;
 1124         vm_prot_t prot;
 1125         vm_offset_t vaddr;
 1126         vm_page_t dst_m;
 1127         vm_page_t src_m;
 1128 
 1129 #ifdef  lint
 1130         src_map++;
 1131 #endif  /* lint */
 1132 
 1133         src_object = src_entry->object.vm_object;
 1134         src_offset = src_entry->offset;
 1135 
 1136         /*
 1137          * Create the top-level object for the destination entry. (Doesn't
 1138          * actually shadow anything - we copy the pages directly.)
 1139          */
 1140         dst_object = vm_object_allocate(OBJT_DEFAULT,
 1141             OFF_TO_IDX(dst_entry->end - dst_entry->start));
 1142 
 1143         VM_OBJECT_LOCK(dst_object);
 1144         dst_entry->object.vm_object = dst_object;
 1145         dst_entry->offset = 0;
 1146 
 1147         prot = dst_entry->max_protection;
 1148 
 1149         /*
 1150          * Loop through all of the pages in the entry's range, copying each
 1151          * one from the source object (it should be there) to the destination
 1152          * object.
 1153          */
 1154         for (vaddr = dst_entry->start, dst_offset = 0;
 1155             vaddr < dst_entry->end;
 1156             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
 1157 
 1158                 /*
 1159                  * Allocate a page in the destination object
 1160                  */
 1161                 do {
 1162                         dst_m = vm_page_alloc(dst_object,
 1163                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
 1164                         if (dst_m == NULL) {
 1165                                 VM_OBJECT_UNLOCK(dst_object);
 1166                                 VM_WAIT;
 1167                                 VM_OBJECT_LOCK(dst_object);
 1168                         }
 1169                 } while (dst_m == NULL);
 1170 
 1171                 /*
 1172                  * Find the page in the source object, and copy it in.
 1173                  * (Because the source is wired down, the page will be in
 1174                  * memory.)
 1175                  */
 1176                 VM_OBJECT_LOCK(src_object);
 1177                 object = src_object;
 1178                 pindex = 0;
 1179                 while ((src_m = vm_page_lookup(object, pindex +
 1180                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
 1181                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
 1182                     (backing_object = object->backing_object) != NULL) {
 1183                         /*
 1184                          * Allow fallback to backing objects if we are reading.
 1185                          */
 1186                         VM_OBJECT_LOCK(backing_object);
 1187                         pindex += OFF_TO_IDX(object->backing_object_offset);
 1188                         VM_OBJECT_UNLOCK(object);
 1189                         object = backing_object;
 1190                 }
 1191                 if (src_m == NULL)
 1192                         panic("vm_fault_copy_wired: page missing");
 1193                 pmap_copy_page(src_m, dst_m);
 1194                 VM_OBJECT_UNLOCK(object);
 1195                 dst_m->valid = VM_PAGE_BITS_ALL;
 1196                 VM_OBJECT_UNLOCK(dst_object);
 1197 
 1198                 /*
 1199                  * Enter it in the pmap...
 1200                  */
 1201                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
 1202                 VM_OBJECT_LOCK(dst_object);
 1203                 vm_page_lock_queues();
 1204                 if ((prot & VM_PROT_WRITE) != 0)
 1205                         vm_page_flag_set(dst_m, PG_WRITEABLE);
 1206 
 1207                 /*
 1208                  * Mark it no longer busy, and put it on the active list.
 1209                  */
 1210                 vm_page_activate(dst_m);
 1211                 vm_page_wakeup(dst_m);
 1212                 vm_page_unlock_queues();
 1213         }
 1214         VM_OBJECT_UNLOCK(dst_object);
 1215 }
 1216 
 1217 
 1218 /*
 1219  * This routine checks around the requested page for other pages that
 1220  * might be able to be faulted in.  This routine brackets the viable
 1221  * pages for the pages to be paged in.
 1222  *
 1223  * Inputs:
 1224  *      m, rbehind, rahead
 1225  *
 1226  * Outputs:
 1227  *  marray (array of vm_page_t), reqpage (index of requested page)
 1228  *
 1229  * Return value:
 1230  *  number of pages in marray
 1231  *
 1232  * This routine can't block.
 1233  */
 1234 static int
 1235 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
 1236         vm_page_t m;
 1237         int rbehind;
 1238         int rahead;
 1239         vm_page_t *marray;
 1240         int *reqpage;
 1241 {
 1242         int i,j;
 1243         vm_object_t object;
 1244         vm_pindex_t pindex, startpindex, endpindex, tpindex;
 1245         vm_page_t rtm;
 1246         int cbehind, cahead;
 1247 
 1248         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
 1249 
 1250         object = m->object;
 1251         pindex = m->pindex;
 1252 
 1253         /*
 1254          * if the requested page is not available, then give up now
 1255          */
 1256         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
 1257                 return 0;
 1258         }
 1259 
 1260         if ((cbehind == 0) && (cahead == 0)) {
 1261                 *reqpage = 0;
 1262                 marray[0] = m;
 1263                 return 1;
 1264         }
 1265 
 1266         if (rahead > cahead) {
 1267                 rahead = cahead;
 1268         }
 1269 
 1270         if (rbehind > cbehind) {
 1271                 rbehind = cbehind;
 1272         }
 1273 
 1274         /*
 1275          * scan backward for the read behind pages -- in memory 
 1276          */
 1277         if (pindex > 0) {
 1278                 if (rbehind > pindex) {
 1279                         rbehind = pindex;
 1280                         startpindex = 0;
 1281                 } else {
 1282                         startpindex = pindex - rbehind;
 1283                 }
 1284 
 1285                 for (tpindex = pindex - 1; tpindex >= startpindex; tpindex -= 1) {
 1286                         if (vm_page_lookup(object, tpindex)) {
 1287                                 startpindex = tpindex + 1;
 1288                                 break;
 1289                         }
 1290                         if (tpindex == 0)
 1291                                 break;
 1292                 }
 1293 
 1294                 /* tpindex is unsigned; beware of numeric underflow. */
 1295                 for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
 1296                     tpindex < pindex; i++, tpindex--) {
 1297 
 1298                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
 1299                         if (rtm == NULL) {
 1300                                 /*
 1301                                  * Shift the allocated pages to the
 1302                                  * beginning of the array.
 1303                                  */
 1304                                 for (j = 0; j < i; j++) {
 1305                                         marray[j] = marray[j + tpindex + 1 -
 1306                                             startpindex];
 1307                                 }
 1308                                 break;
 1309                         }
 1310 
 1311                         marray[tpindex - startpindex] = rtm;
 1312                 }
 1313         } else {
 1314                 startpindex = 0;
 1315                 i = 0;
 1316         }
 1317 
 1318         marray[i] = m;
 1319         /* page offset of the required page */
 1320         *reqpage = i;
 1321 
 1322         tpindex = pindex + 1;
 1323         i++;
 1324 
 1325         /*
 1326          * scan forward for the read ahead pages
 1327          */
 1328         endpindex = tpindex + rahead;
 1329         if (endpindex > object->size)
 1330                 endpindex = object->size;
 1331 
 1332         for (; tpindex < endpindex; i++, tpindex++) {
 1333 
 1334                 if (vm_page_lookup(object, tpindex)) {
 1335                         break;
 1336                 }
 1337 
 1338                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
 1339                 if (rtm == NULL) {
 1340                         break;
 1341                 }
 1342 
 1343                 marray[i] = rtm;
 1344         }
 1345 
 1346         /* return number of pages */
 1347         return i;
 1348 }

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