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

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