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 #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, alloc_req;
  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                          * Unlocked read of the p_flag is harmless. At
  454                          * worst, the P_KILLED might be not observed
  455                          * there, and allocation can fail, causing
  456                          * restart and new reading of the p_flag.
  457                          */
  458                         fs.m = NULL;
  459                         if (!vm_page_count_severe() || P_KILLED(curproc)) {
  460                                 alloc_req = P_KILLED(curproc) ?
  461                                     VM_ALLOC_SYSTEM : VM_ALLOC_NORMAL;
  462                                 if (fs.vp == NULL &&
  463                                     fs.object->backing_object == NULL)
  464                                         alloc_req |= VM_ALLOC_ZERO;
  465                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
  466                                     alloc_req);
  467                         }
  468                         if (fs.m == NULL) {
  469                                 unlock_and_deallocate(&fs);
  470                                 VM_WAITPFAULT;
  471                                 goto RetryFault;
  472                         }
  473                 }
  474 
  475 readrest:
  476                 /*
  477                  * We have found a valid page or we have allocated a new page.
  478                  * The page thus may not be valid or may not be entirely 
  479                  * valid.
  480                  *
  481                  * Attempt to fault-in the page if there is a chance that the
  482                  * pager has it, and potentially fault in additional pages
  483                  * at the same time.
  484                  */
  485                 if (TRYPAGER) {
  486                         int rv;
  487                         int reqpage;
  488                         int ahead, behind;
  489                         u_char behavior = vm_map_entry_behavior(fs.entry);
  490 
  491                         if (behavior == MAP_ENTRY_BEHAV_RANDOM ||
  492                             P_KILLED(curproc)) {
  493                                 ahead = 0;
  494                                 behind = 0;
  495                         } else {
  496                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
  497                                 if (behind > VM_FAULT_READ_BEHIND)
  498                                         behind = VM_FAULT_READ_BEHIND;
  499 
  500                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
  501                                 if (ahead > VM_FAULT_READ_AHEAD)
  502                                         ahead = VM_FAULT_READ_AHEAD;
  503                         }
  504                         is_first_object_locked = FALSE;
  505                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
  506                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
  507                               fs.pindex >= fs.entry->lastr &&
  508                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
  509                             (fs.first_object == fs.object ||
  510                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
  511                             fs.first_object->type != OBJT_DEVICE) {
  512                                 vm_pindex_t firstpindex, tmppindex;
  513 
  514                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
  515                                         firstpindex = 0;
  516                                 else
  517                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
  518 
  519                                 vm_page_lock_queues();
  520                                 /*
  521                                  * note: partially valid pages cannot be 
  522                                  * included in the lookahead - NFS piecemeal
  523                                  * writes will barf on it badly.
  524                                  */
  525                                 for (tmppindex = fs.first_pindex - 1;
  526                                         tmppindex >= firstpindex;
  527                                         --tmppindex) {
  528                                         vm_page_t mt;
  529 
  530                                         mt = vm_page_lookup(fs.first_object, tmppindex);
  531                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
  532                                                 break;
  533                                         if (mt->busy ||
  534                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
  535                                                 mt->hold_count ||
  536                                                 mt->wire_count) 
  537                                                 continue;
  538                                         pmap_remove_all(mt);
  539                                         if (mt->dirty) {
  540                                                 vm_page_deactivate(mt);
  541                                         } else {
  542                                                 vm_page_cache(mt);
  543                                         }
  544                                 }
  545                                 vm_page_unlock_queues();
  546                                 ahead += behind;
  547                                 behind = 0;
  548                         }
  549                         if (is_first_object_locked)
  550                                 VM_OBJECT_UNLOCK(fs.first_object);
  551                         /*
  552                          * now we find out if any other pages should be paged
  553                          * in at this time this routine checks to see if the
  554                          * pages surrounding this fault reside in the same
  555                          * object as the page for this fault.  If they do,
  556                          * then they are faulted in also into the object.  The
  557                          * array "marray" returned contains an array of
  558                          * vm_page_t structs where one of them is the
  559                          * vm_page_t passed to the routine.  The reqpage
  560                          * return value is the index into the marray for the
  561                          * vm_page_t passed to the routine.
  562                          *
  563                          * fs.m plus the additional pages are PG_BUSY'd.
  564                          *
  565                          * XXX vm_fault_additional_pages() can block
  566                          * without releasing the map lock.
  567                          */
  568                         faultcount = vm_fault_additional_pages(
  569                             fs.m, behind, ahead, marray, &reqpage);
  570 
  571                         /*
  572                          * update lastr imperfectly (we do not know how much
  573                          * getpages will actually read), but good enough.
  574                          *
  575                          * XXX The following assignment modifies the map
  576                          * without holding a write lock on it.
  577                          */
  578                         fs.entry->lastr = fs.pindex + faultcount - behind;
  579 
  580                         /*
  581                          * Call the pager to retrieve the data, if any, after
  582                          * releasing the lock on the map.  We hold a ref on
  583                          * fs.object and the pages are PG_BUSY'd.
  584                          */
  585                         unlock_map(&fs);
  586 
  587                         rv = faultcount ?
  588                             vm_pager_get_pages(fs.object, marray, faultcount,
  589                                 reqpage) : VM_PAGER_FAIL;
  590 
  591                         if (rv == VM_PAGER_OK) {
  592                                 /*
  593                                  * Found the page. Leave it busy while we play
  594                                  * with it.
  595                                  */
  596 
  597                                 /*
  598                                  * Relookup in case pager changed page. Pager
  599                                  * is responsible for disposition of old page
  600                                  * if moved.
  601                                  */
  602                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
  603                                 if (!fs.m) {
  604                                         unlock_and_deallocate(&fs);
  605                                         goto RetryFault;
  606                                 }
  607 
  608                                 hardfault++;
  609                                 break; /* break to PAGE HAS BEEN FOUND */
  610                         }
  611                         /*
  612                          * Remove the bogus page (which does not exist at this
  613                          * object/offset); before doing so, we must get back
  614                          * our object lock to preserve our invariant.
  615                          *
  616                          * Also wake up any other process that may want to bring
  617                          * in this page.
  618                          *
  619                          * If this is the top-level object, we must leave the
  620                          * busy page to prevent another process from rushing
  621                          * past us, and inserting the page in that object at
  622                          * the same time that we are.
  623                          */
  624                         if (rv == VM_PAGER_ERROR)
  625                                 printf("vm_fault: pager read error, pid %d (%s)\n",
  626                                     curproc->p_pid, curproc->p_comm);
  627                         /*
  628                          * Data outside the range of the pager or an I/O error
  629                          */
  630                         /*
  631                          * XXX - the check for kernel_map is a kludge to work
  632                          * around having the machine panic on a kernel space
  633                          * fault w/ I/O error.
  634                          */
  635                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
  636                                 (rv == VM_PAGER_BAD)) {
  637                                 vm_page_lock_queues();
  638                                 vm_page_free(fs.m);
  639                                 vm_page_unlock_queues();
  640                                 fs.m = NULL;
  641                                 unlock_and_deallocate(&fs);
  642                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
  643                         }
  644                         if (fs.object != fs.first_object) {
  645                                 vm_page_lock_queues();
  646                                 vm_page_free(fs.m);
  647                                 vm_page_unlock_queues();
  648                                 fs.m = NULL;
  649                                 /*
  650                                  * XXX - we cannot just fall out at this
  651                                  * point, m has been freed and is invalid!
  652                                  */
  653                         }
  654                 }
  655 
  656                 /*
  657                  * We get here if the object has default pager (or unwiring) 
  658                  * or the pager doesn't have the page.
  659                  */
  660                 if (fs.object == fs.first_object)
  661                         fs.first_m = fs.m;
  662 
  663                 /*
  664                  * Move on to the next object.  Lock the next object before
  665                  * unlocking the current one.
  666                  */
  667                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
  668                 next_object = fs.object->backing_object;
  669                 if (next_object == NULL) {
  670                         /*
  671                          * If there's no object left, fill the page in the top
  672                          * object with zeros.
  673                          */
  674                         if (fs.object != fs.first_object) {
  675                                 vm_object_pip_wakeup(fs.object);
  676                                 VM_OBJECT_UNLOCK(fs.object);
  677 
  678                                 fs.object = fs.first_object;
  679                                 fs.pindex = fs.first_pindex;
  680                                 fs.m = fs.first_m;
  681                                 VM_OBJECT_LOCK(fs.object);
  682                         }
  683                         fs.first_m = NULL;
  684 
  685                         /*
  686                          * Zero the page if necessary and mark it valid.
  687                          */
  688                         if ((fs.m->flags & PG_ZERO) == 0) {
  689                                 pmap_zero_page(fs.m);
  690                         } else {
  691                                 atomic_add_int(&cnt.v_ozfod, 1);
  692                         }
  693                         atomic_add_int(&cnt.v_zfod, 1);
  694                         fs.m->valid = VM_PAGE_BITS_ALL;
  695                         break;  /* break to PAGE HAS BEEN FOUND */
  696                 } else {
  697                         KASSERT(fs.object != next_object,
  698                             ("object loop %p", next_object));
  699                         VM_OBJECT_LOCK(next_object);
  700                         vm_object_pip_add(next_object, 1);
  701                         if (fs.object != fs.first_object)
  702                                 vm_object_pip_wakeup(fs.object);
  703                         VM_OBJECT_UNLOCK(fs.object);
  704                         fs.object = next_object;
  705                 }
  706         }
  707 
  708         KASSERT((fs.m->flags & PG_BUSY) != 0,
  709             ("vm_fault: not busy after main loop"));
  710 
  711         /*
  712          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
  713          * is held.]
  714          */
  715 
  716         /*
  717          * If the page is being written, but isn't already owned by the
  718          * top-level object, we have to copy it into a new page owned by the
  719          * top-level object.
  720          */
  721         if (fs.object != fs.first_object) {
  722                 /*
  723                  * We only really need to copy if we want to write it.
  724                  */
  725                 if (fault_type & VM_PROT_WRITE) {
  726                         /*
  727                          * This allows pages to be virtually copied from a 
  728                          * backing_object into the first_object, where the 
  729                          * backing object has no other refs to it, and cannot
  730                          * gain any more refs.  Instead of a bcopy, we just 
  731                          * move the page from the backing object to the 
  732                          * first object.  Note that we must mark the page 
  733                          * dirty in the first object so that it will go out 
  734                          * to swap when needed.
  735                          */
  736                         is_first_object_locked = FALSE;
  737                         if (
  738                                 /*
  739                                  * Only one shadow object
  740                                  */
  741                                 (fs.object->shadow_count == 1) &&
  742                                 /*
  743                                  * No COW refs, except us
  744                                  */
  745                                 (fs.object->ref_count == 1) &&
  746                                 /*
  747                                  * No one else can look this object up
  748                                  */
  749                                 (fs.object->handle == NULL) &&
  750                                 /*
  751                                  * No other ways to look the object up
  752                                  */
  753                                 ((fs.object->type == OBJT_DEFAULT) ||
  754                                  (fs.object->type == OBJT_SWAP)) &&
  755                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
  756                                 /*
  757                                  * We don't chase down the shadow chain
  758                                  */
  759                             fs.object == fs.first_object->backing_object) {
  760                                 vm_page_lock_queues();
  761                                 /*
  762                                  * get rid of the unnecessary page
  763                                  */
  764                                 pmap_remove_all(fs.first_m);
  765                                 vm_page_free(fs.first_m);
  766                                 /*
  767                                  * grab the page and put it into the 
  768                                  * process'es object.  The page is 
  769                                  * automatically made dirty.
  770                                  */
  771                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
  772                                 vm_page_busy(fs.m);
  773                                 vm_page_unlock_queues();
  774                                 fs.first_m = fs.m;
  775                                 fs.m = NULL;
  776                                 atomic_add_int(&cnt.v_cow_optim, 1);
  777                         } else {
  778                                 /*
  779                                  * Oh, well, lets copy it.
  780                                  */
  781                                 pmap_copy_page(fs.m, fs.first_m);
  782                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
  783                         }
  784                         if (fs.m) {
  785                                 /*
  786                                  * We no longer need the old page or object.
  787                                  */
  788                                 release_page(&fs);
  789                         }
  790                         /*
  791                          * fs.object != fs.first_object due to above 
  792                          * conditional
  793                          */
  794                         vm_object_pip_wakeup(fs.object);
  795                         VM_OBJECT_UNLOCK(fs.object);
  796                         /*
  797                          * Only use the new page below...
  798                          */
  799                         fs.object = fs.first_object;
  800                         fs.pindex = fs.first_pindex;
  801                         fs.m = fs.first_m;
  802                         if (!is_first_object_locked)
  803                                 VM_OBJECT_LOCK(fs.object);
  804                         atomic_add_int(&cnt.v_cow_faults, 1);
  805                 } else {
  806                         prot &= ~VM_PROT_WRITE;
  807                 }
  808         }
  809 
  810         /*
  811          * We must verify that the maps have not changed since our last
  812          * lookup.
  813          */
  814         if (!fs.lookup_still_valid) {
  815                 vm_object_t retry_object;
  816                 vm_pindex_t retry_pindex;
  817                 vm_prot_t retry_prot;
  818 
  819                 if (!vm_map_trylock_read(fs.map)) {
  820                         release_page(&fs);
  821                         unlock_and_deallocate(&fs);
  822                         goto RetryFault;
  823                 }
  824                 fs.lookup_still_valid = TRUE;
  825                 if (fs.map->timestamp != map_generation) {
  826                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
  827                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
  828 
  829                         /*
  830                          * If we don't need the page any longer, put it on the inactive
  831                          * list (the easiest thing to do here).  If no one needs it,
  832                          * pageout will grab it eventually.
  833                          */
  834                         if (result != KERN_SUCCESS) {
  835                                 release_page(&fs);
  836                                 unlock_and_deallocate(&fs);
  837 
  838                                 /*
  839                                  * If retry of map lookup would have blocked then
  840                                  * retry fault from start.
  841                                  */
  842                                 if (result == KERN_FAILURE)
  843                                         goto RetryFault;
  844                                 return (result);
  845                         }
  846                         if ((retry_object != fs.first_object) ||
  847                             (retry_pindex != fs.first_pindex)) {
  848                                 release_page(&fs);
  849                                 unlock_and_deallocate(&fs);
  850                                 goto RetryFault;
  851                         }
  852 
  853                         /*
  854                          * Check whether the protection has changed or the object has
  855                          * been copied while we left the map unlocked. Changing from
  856                          * read to write permission is OK - we leave the page
  857                          * write-protected, and catch the write fault. Changing from
  858                          * write to read permission means that we can't mark the page
  859                          * write-enabled after all.
  860                          */
  861                         prot &= retry_prot;
  862                 }
  863         }
  864         if (prot & VM_PROT_WRITE) {
  865                 vm_page_lock_queues();
  866                 vm_page_flag_set(fs.m, PG_WRITEABLE);
  867                 vm_object_set_writeable_dirty(fs.m->object);
  868 
  869                 /*
  870                  * If the fault is a write, we know that this page is being
  871                  * written NOW so dirty it explicitly to save on 
  872                  * pmap_is_modified() calls later.
  873                  *
  874                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
  875                  * if the page is already dirty to prevent data written with
  876                  * the expectation of being synced from not being synced.
  877                  * Likewise if this entry does not request NOSYNC then make
  878                  * sure the page isn't marked NOSYNC.  Applications sharing
  879                  * data should use the same flags to avoid ping ponging.
  880                  *
  881                  * Also tell the backing pager, if any, that it should remove
  882                  * any swap backing since the page is now dirty.
  883                  */
  884                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
  885                         if (fs.m->dirty == 0)
  886                                 vm_page_flag_set(fs.m, PG_NOSYNC);
  887                 } else {
  888                         vm_page_flag_clear(fs.m, PG_NOSYNC);
  889                 }
  890                 vm_page_unlock_queues();
  891                 if (fault_flags & VM_FAULT_DIRTY) {
  892                         vm_page_dirty(fs.m);
  893                         vm_pager_page_unswapped(fs.m);
  894                 }
  895         }
  896 
  897         /*
  898          * Page had better still be busy
  899          */
  900         KASSERT(fs.m->flags & PG_BUSY,
  901                 ("vm_fault: page %p not busy!", fs.m));
  902         /*
  903          * Sanity check: page must be completely valid or it is not fit to
  904          * map into user space.  vm_pager_get_pages() ensures this.
  905          */
  906         if (fs.m->valid != VM_PAGE_BITS_ALL) {
  907                 vm_page_zero_invalid(fs.m, TRUE);
  908                 printf("Warning: page %p partially invalid on fault\n", fs.m);
  909         }
  910         VM_OBJECT_UNLOCK(fs.object);
  911 
  912         /*
  913          * Put this page into the physical map.  We had to do the unlock above
  914          * because pmap_enter() may sleep.  We don't put the page
  915          * back on the active queue until later so that the pageout daemon
  916          * won't find it (yet).
  917          */
  918         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
  919         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
  920                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
  921         }
  922         VM_OBJECT_LOCK(fs.object);
  923         vm_page_lock_queues();
  924         vm_page_flag_set(fs.m, PG_REFERENCED);
  925 
  926         /*
  927          * If the page is not wired down, then put it where the pageout daemon
  928          * can find it.
  929          */
  930         if (fault_flags & VM_FAULT_WIRE_MASK) {
  931                 if (wired)
  932                         vm_page_wire(fs.m);
  933                 else
  934                         vm_page_unwire(fs.m, 1);
  935         } else {
  936                 vm_page_activate(fs.m);
  937         }
  938         vm_page_wakeup(fs.m);
  939         vm_page_unlock_queues();
  940 
  941         /*
  942          * Unlock everything, and return
  943          */
  944         unlock_and_deallocate(&fs);
  945         PROC_LOCK(curproc);
  946         if ((curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
  947                 if (hardfault) {
  948                         curproc->p_stats->p_ru.ru_majflt++;
  949                 } else {
  950                         curproc->p_stats->p_ru.ru_minflt++;
  951                 }
  952         }
  953         PROC_UNLOCK(curproc);
  954 
  955         return (KERN_SUCCESS);
  956 }
  957 
  958 /*
  959  * vm_fault_prefault provides a quick way of clustering
  960  * pagefaults into a processes address space.  It is a "cousin"
  961  * of vm_map_pmap_enter, except it runs at page fault time instead
  962  * of mmap time.
  963  */
  964 static void
  965 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
  966 {
  967         int i;
  968         vm_offset_t addr, starta;
  969         vm_pindex_t pindex;
  970         vm_page_t m;
  971         vm_object_t object;
  972 
  973         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
  974                 return;
  975 
  976         object = entry->object.vm_object;
  977 
  978         starta = addra - PFBAK * PAGE_SIZE;
  979         if (starta < entry->start) {
  980                 starta = entry->start;
  981         } else if (starta > addra) {
  982                 starta = 0;
  983         }
  984 
  985         for (i = 0; i < PAGEORDER_SIZE; i++) {
  986                 vm_object_t backing_object, lobject;
  987 
  988                 addr = addra + prefault_pageorder[i];
  989                 if (addr > addra + (PFFOR * PAGE_SIZE))
  990                         addr = 0;
  991 
  992                 if (addr < starta || addr >= entry->end)
  993                         continue;
  994 
  995                 if (!pmap_is_prefaultable(pmap, addr))
  996                         continue;
  997 
  998                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
  999                 lobject = object;
 1000                 VM_OBJECT_LOCK(lobject);
 1001                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
 1002                     lobject->type == OBJT_DEFAULT &&
 1003                     (backing_object = lobject->backing_object) != NULL) {
 1004                         if (lobject->backing_object_offset & PAGE_MASK)
 1005                                 break;
 1006                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
 1007                         VM_OBJECT_LOCK(backing_object);
 1008                         VM_OBJECT_UNLOCK(lobject);
 1009                         lobject = backing_object;
 1010                 }
 1011                 /*
 1012                  * give-up when a page is not in memory
 1013                  */
 1014                 if (m == NULL) {
 1015                         VM_OBJECT_UNLOCK(lobject);
 1016                         break;
 1017                 }
 1018                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
 1019                         (m->busy == 0) &&
 1020                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
 1021 
 1022                         vm_page_lock_queues();
 1023                         if ((m->queue - m->pc) == PQ_CACHE)
 1024                                 vm_page_deactivate(m);
 1025                         pmap_enter_quick(pmap, addr, m, entry->protection);
 1026                         vm_page_unlock_queues();
 1027                 }
 1028                 VM_OBJECT_UNLOCK(lobject);
 1029         }
 1030 }
 1031 
 1032 /*
 1033  *      vm_fault_quick:
 1034  *
 1035  *      Ensure that the requested virtual address, which may be in userland,
 1036  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
 1037  */
 1038 int
 1039 vm_fault_quick(caddr_t v, int prot)
 1040 {
 1041         int r;
 1042 
 1043         if (prot & VM_PROT_WRITE)
 1044                 r = subyte(v, fubyte(v));
 1045         else
 1046                 r = fubyte(v);
 1047         return(r);
 1048 }
 1049 
 1050 /*
 1051  *      vm_fault_wire:
 1052  *
 1053  *      Wire down a range of virtual addresses in a map.
 1054  */
 1055 int
 1056 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1057     boolean_t user_wire, boolean_t fictitious)
 1058 {
 1059         vm_offset_t va;
 1060         int rv;
 1061 
 1062         /*
 1063          * We simulate a fault to get the page and enter it in the physical
 1064          * map.  For user wiring, we only ask for read access on currently
 1065          * read-only sections.
 1066          */
 1067         for (va = start; va < end; va += PAGE_SIZE) {
 1068                 rv = vm_fault(map, va,
 1069                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
 1070                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
 1071                 if (rv) {
 1072                         if (va != start)
 1073                                 vm_fault_unwire(map, start, va, fictitious);
 1074                         return (rv);
 1075                 }
 1076         }
 1077         return (KERN_SUCCESS);
 1078 }
 1079 
 1080 /*
 1081  *      vm_fault_unwire:
 1082  *
 1083  *      Unwire a range of virtual addresses in a map.
 1084  */
 1085 void
 1086 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 1087     boolean_t fictitious)
 1088 {
 1089         vm_paddr_t pa;
 1090         vm_offset_t va;
 1091         pmap_t pmap;
 1092 
 1093         pmap = vm_map_pmap(map);
 1094 
 1095         /*
 1096          * Since the pages are wired down, we must be able to get their
 1097          * mappings from the physical map system.
 1098          */
 1099         for (va = start; va < end; va += PAGE_SIZE) {
 1100                 pa = pmap_extract(pmap, va);
 1101                 if (pa != 0) {
 1102                         pmap_change_wiring(pmap, va, FALSE);
 1103                         if (!fictitious) {
 1104                                 vm_page_lock_queues();
 1105                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
 1106                                 vm_page_unlock_queues();
 1107                         }
 1108                 }
 1109         }
 1110 }
 1111 
 1112 /*
 1113  *      Routine:
 1114  *              vm_fault_copy_entry
 1115  *      Function:
 1116  *              Copy all of the pages from a wired-down map entry to another.
 1117  *
 1118  *      In/out conditions:
 1119  *              The source and destination maps must be locked for write.
 1120  *              The source map entry must be wired down (or be a sharing map
 1121  *              entry corresponding to a main map entry that is wired down).
 1122  */
 1123 void
 1124 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
 1125         vm_map_t dst_map;
 1126         vm_map_t src_map;
 1127         vm_map_entry_t dst_entry;
 1128         vm_map_entry_t src_entry;
 1129 {
 1130         vm_object_t backing_object, dst_object, object;
 1131         vm_object_t src_object;
 1132         vm_ooffset_t dst_offset;
 1133         vm_ooffset_t src_offset;
 1134         vm_pindex_t pindex;
 1135         vm_prot_t prot;
 1136         vm_offset_t vaddr;
 1137         vm_page_t dst_m;
 1138         vm_page_t src_m;
 1139 
 1140 #ifdef  lint
 1141         src_map++;
 1142 #endif  /* lint */
 1143 
 1144         src_object = src_entry->object.vm_object;
 1145         src_offset = src_entry->offset;
 1146 
 1147         /*
 1148          * Create the top-level object for the destination entry. (Doesn't
 1149          * actually shadow anything - we copy the pages directly.)
 1150          */
 1151         dst_object = vm_object_allocate(OBJT_DEFAULT,
 1152             OFF_TO_IDX(dst_entry->end - dst_entry->start));
 1153 
 1154         VM_OBJECT_LOCK(dst_object);
 1155         dst_entry->object.vm_object = dst_object;
 1156         dst_entry->offset = 0;
 1157 
 1158         prot = dst_entry->max_protection;
 1159 
 1160         /*
 1161          * Loop through all of the pages in the entry's range, copying each
 1162          * one from the source object (it should be there) to the destination
 1163          * object.
 1164          */
 1165         for (vaddr = dst_entry->start, dst_offset = 0;
 1166             vaddr < dst_entry->end;
 1167             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
 1168 
 1169                 /*
 1170                  * Allocate a page in the destination object
 1171                  */
 1172                 do {
 1173                         dst_m = vm_page_alloc(dst_object,
 1174                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
 1175                         if (dst_m == NULL) {
 1176                                 VM_OBJECT_UNLOCK(dst_object);
 1177                                 VM_WAIT;
 1178                                 VM_OBJECT_LOCK(dst_object);
 1179                         }
 1180                 } while (dst_m == NULL);
 1181 
 1182                 /*
 1183                  * Find the page in the source object, and copy it in.
 1184                  * (Because the source is wired down, the page will be in
 1185                  * memory.)
 1186                  */
 1187                 VM_OBJECT_LOCK(src_object);
 1188                 object = src_object;
 1189                 pindex = 0;
 1190                 while ((src_m = vm_page_lookup(object, pindex +
 1191                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
 1192                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
 1193                     (backing_object = object->backing_object) != NULL) {
 1194                         /*
 1195                          * Allow fallback to backing objects if we are reading.
 1196                          */
 1197                         VM_OBJECT_LOCK(backing_object);
 1198                         pindex += OFF_TO_IDX(object->backing_object_offset);
 1199                         VM_OBJECT_UNLOCK(object);
 1200                         object = backing_object;
 1201                 }
 1202                 if (src_m == NULL)
 1203                         panic("vm_fault_copy_wired: page missing");
 1204                 pmap_copy_page(src_m, dst_m);
 1205                 VM_OBJECT_UNLOCK(object);
 1206                 dst_m->valid = VM_PAGE_BITS_ALL;
 1207                 VM_OBJECT_UNLOCK(dst_object);
 1208 
 1209                 /*
 1210                  * Enter it in the pmap...
 1211                  */
 1212                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
 1213                 VM_OBJECT_LOCK(dst_object);
 1214                 vm_page_lock_queues();
 1215                 if ((prot & VM_PROT_WRITE) != 0)
 1216                         vm_page_flag_set(dst_m, PG_WRITEABLE);
 1217 
 1218                 /*
 1219                  * Mark it no longer busy, and put it on the active list.
 1220                  */
 1221                 vm_page_activate(dst_m);
 1222                 vm_page_wakeup(dst_m);
 1223                 vm_page_unlock_queues();
 1224         }
 1225         VM_OBJECT_UNLOCK(dst_object);
 1226 }
 1227 
 1228 
 1229 /*
 1230  * This routine checks around the requested page for other pages that
 1231  * might be able to be faulted in.  This routine brackets the viable
 1232  * pages for the pages to be paged in.
 1233  *
 1234  * Inputs:
 1235  *      m, rbehind, rahead
 1236  *
 1237  * Outputs:
 1238  *  marray (array of vm_page_t), reqpage (index of requested page)
 1239  *
 1240  * Return value:
 1241  *  number of pages in marray
 1242  *
 1243  * This routine can't block.
 1244  */
 1245 static int
 1246 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
 1247         vm_page_t m;
 1248         int rbehind;
 1249         int rahead;
 1250         vm_page_t *marray;
 1251         int *reqpage;
 1252 {
 1253         int i,j;
 1254         vm_object_t object;
 1255         vm_pindex_t pindex, startpindex, endpindex, tpindex;
 1256         vm_page_t rtm;
 1257         int cbehind, cahead;
 1258 
 1259         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
 1260 
 1261         object = m->object;
 1262         pindex = m->pindex;
 1263 
 1264         /*
 1265          * if the requested page is not available, then give up now
 1266          */
 1267         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
 1268                 return 0;
 1269         }
 1270 
 1271         if ((cbehind == 0) && (cahead == 0)) {
 1272                 *reqpage = 0;
 1273                 marray[0] = m;
 1274                 return 1;
 1275         }
 1276 
 1277         if (rahead > cahead) {
 1278                 rahead = cahead;
 1279         }
 1280 
 1281         if (rbehind > cbehind) {
 1282                 rbehind = cbehind;
 1283         }
 1284 
 1285         /*
 1286          * scan backward for the read behind pages -- in memory 
 1287          */
 1288         if (pindex > 0) {
 1289                 if (rbehind > pindex) {
 1290                         rbehind = pindex;
 1291                         startpindex = 0;
 1292                 } else {
 1293                         startpindex = pindex - rbehind;
 1294                 }
 1295 
 1296                 for (tpindex = pindex - 1; tpindex >= startpindex; tpindex -= 1) {
 1297                         if (vm_page_lookup(object, tpindex)) {
 1298                                 startpindex = tpindex + 1;
 1299                                 break;
 1300                         }
 1301                         if (tpindex == 0)
 1302                                 break;
 1303                 }
 1304 
 1305                 /* tpindex is unsigned; beware of numeric underflow. */
 1306                 for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
 1307                     tpindex < pindex; i++, tpindex--) {
 1308 
 1309                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
 1310                         if (rtm == NULL) {
 1311                                 /*
 1312                                  * Shift the allocated pages to the
 1313                                  * beginning of the array.
 1314                                  */
 1315                                 for (j = 0; j < i; j++) {
 1316                                         marray[j] = marray[j + tpindex + 1 -
 1317                                             startpindex];
 1318                                 }
 1319                                 break;
 1320                         }
 1321 
 1322                         marray[tpindex - startpindex] = 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 pages */
 1358         return i;
 1359 }

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