sys/vm/vm_fault.c

   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 "opt_vm.h"
  78
  79 #include <sys/param.h>
  80 #include <sys/systm.h>
  81 #include <sys/kernel.h>
  82 #include <sys/lock.h>
  83 #include <sys/mutex.h>
  84 #include <sys/proc.h>
  85 #include <sys/resourcevar.h>
  86 #include <sys/sysctl.h>
  87 #include <sys/vmmeter.h>
  88 #include <sys/vnode.h>
  89
  90 #include <vm/vm.h>
  91 #include <vm/vm_param.h>
  92 #include <vm/pmap.h>
  93 #include <vm/vm_map.h>
  94 #include <vm/vm_object.h>
  95 #include <vm/vm_page.h>
  96 #include <vm/vm_pageout.h>
  97 #include <vm/vm_kern.h>
  98 #include <vm/vm_pager.h>
  99 #include <vm/vm_extern.h>
 100
 101 #include <sys/mount.h>  /* XXX Temporary for VFS_LOCK_GIANT() */
 102
 103 #define PFBAK 4
 104 #define PFFOR 4
 105 #define PAGEORDER_SIZE (PFBAK+PFFOR)
 106
 107 static int prefault_pageorder[] = {
 108         -1 * PAGE_SIZE, 1 * PAGE_SIZE,
 109         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
 110         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
 111         -4 * PAGE_SIZE, 4 * PAGE_SIZE
 112 };
 113
 114 static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
 115 static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
 116
 117 #define VM_FAULT_READ_AHEAD 8
 118 #define VM_FAULT_READ_BEHIND 7
 119 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
 120
 121 struct faultstate {
 122         vm_page_t m;
 123         vm_object_t object;
 124         vm_pindex_t pindex;
 125         vm_page_t first_m;
 126         vm_object_t     first_object;
 127         vm_pindex_t first_pindex;
 128         vm_map_t map;
 129         vm_map_entry_t entry;
 130         int lookup_still_valid;
 131         struct vnode *vp;
 132         int vfslocked;
 133 };
 134
 135 static inline void
 136 release_page(struct faultstate *fs)
 137 {
 138
 139         vm_page_wakeup(fs->m);
 140         vm_page_lock_queues();
 141         vm_page_deactivate(fs->m);
 142         vm_page_unlock_queues();
 143         fs->m = NULL;
 144 }
 145
 146 static inline void
 147 unlock_map(struct faultstate *fs)
 148 {
 149
 150         if (fs->lookup_still_valid) {
 151                 vm_map_lookup_done(fs->map, fs->entry);
 152                 fs->lookup_still_valid = FALSE;
 153         }
 154 }
 155
 156 static void
 157 unlock_and_deallocate(struct faultstate *fs)
 158 {
 159
 160         vm_object_pip_wakeup(fs->object);
 161         VM_OBJECT_UNLOCK(fs->object);
 162         if (fs->object != fs->first_object) {
 163                 VM_OBJECT_LOCK(fs->first_object);
 164                 vm_page_lock_queues();
 165                 vm_page_free(fs->first_m);
 166                 vm_page_unlock_queues();
 167                 vm_object_pip_wakeup(fs->first_object);
 168                 VM_OBJECT_UNLOCK(fs->first_object);
 169                 fs->first_m = NULL;
 170         }
 171         vm_object_deallocate(fs->first_object);
 172         unlock_map(fs);
 173         if (fs->vp != NULL) {
 174                 vput(fs->vp);
 175                 fs->vp = NULL;
 176         }
 177         VFS_UNLOCK_GIANT(fs->vfslocked);
 178         fs->vfslocked = 0;
 179 }
 180
 181 /*
 182  * TRYPAGER - used by vm_fault to calculate whether the pager for the
 183  *            current object *might* contain the page.
 184  *
 185  *            default objects are zero-fill, there is no real pager.
 186  */
 187 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
 188                         ((fault_flags & VM_FAULT_CHANGE_WIRING) == 0 || wired))
 189
 190 /*
 191  *      vm_fault:
 192  *
 193  *      Handle a page fault occurring at the given address,
 194  *      requiring the given permissions, in the map specified.
 195  *      If successful, the page is inserted into the
 196  *      associated physical map.
 197  *
 198  *      NOTE: the given address should be truncated to the
 199  *      proper page address.
 200  *
 201  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 202  *      a standard error specifying why the fault is fatal is returned.
 203  *
 204  *
 205  *      The map in question must be referenced, and remains so.
 206  *      Caller may hold no locks.
 207  */
 208 int
 209 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 210          int fault_flags)
 211 {
 212         vm_prot_t prot;
 213         int is_first_object_locked, result;
 214         boolean_t are_queues_locked, growstack, wired;
 215         int map_generation;
 216         vm_object_t next_object;
 217         vm_page_t marray[VM_FAULT_READ];
 218         int hardfault;
 219         int faultcount, ahead, behind;
 220         struct faultstate fs;
 221         struct vnode *vp;
 222         int locked, error;
 223
 224         hardfault = 0;
 225         growstack = TRUE;
 226         PCPU_INC(cnt.v_vm_faults);
 227         fs.vp = NULL;
 228         fs.vfslocked = 0;
 229         faultcount = behind = 0;
 230
 231 RetryFault:;
 232
 233         /*
 234          * Find the backing store object and offset into it to begin the
 235          * search.
 236          */
 237         fs.map = map;
 238         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
 239             &fs.first_object, &fs.first_pindex, &prot, &wired);
 240         if (result != KERN_SUCCESS) {
 241                 if (growstack && result == KERN_INVALID_ADDRESS &&
 242                     map != kernel_map) {
 243                         result = vm_map_growstack(curproc, vaddr);
 244                         if (result != KERN_SUCCESS)
 245                                 return (KERN_FAILURE);
 246                         growstack = FALSE;
 247                         goto RetryFault;
 248                 }
 249                 return (result);
 250         }
 251
 252         map_generation = fs.map->timestamp;
 253
 254         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 255                 panic("vm_fault: fault on nofault entry, addr: %lx",
 256                     (u_long)vaddr);
 257         }
 258
 259         /*
 260          * Make a reference to this object to prevent its disposal while we
 261          * are messing with it.  Once we have the reference, the map is free
 262          * to be diddled.  Since objects reference their shadows (and copies),
 263          * they will stay around as well.
 264          *
 265          * Bump the paging-in-progress count to prevent size changes (e.g.
 266          * truncation operations) during I/O.  This must be done after
 267          * obtaining the vnode lock in order to avoid possible deadlocks.
 268          */
 269         VM_OBJECT_LOCK(fs.first_object);
 270         vm_object_reference_locked(fs.first_object);
 271         vm_object_pip_add(fs.first_object, 1);
 272
 273         fs.lookup_still_valid = TRUE;
 274
 275         if (wired)
 276                 fault_type = prot | (fault_type & VM_PROT_COPY);
 277
 278         fs.first_m = NULL;
 279
 280         /*
 281          * Search for the page at object/offset.
 282          */
 283         fs.object = fs.first_object;
 284         fs.pindex = fs.first_pindex;
 285         while (TRUE) {
 286                 /*
 287                  * If the object is dead, we stop here
 288                  */
 289                 if (fs.object->flags & OBJ_DEAD) {
 290                         unlock_and_deallocate(&fs);
 291                         return (KERN_PROTECTION_FAILURE);
 292                 }
 293
 294                 /*
 295                  * See if page is resident
 296                  */
 297                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 298                 if (fs.m != NULL) {
 299                         /*
 300                          * check for page-based copy on write.
 301                          * We check fs.object == fs.first_object so
 302                          * as to ensure the legacy COW mechanism is
 303                          * used when the page in question is part of
 304                          * a shadow object.  Otherwise, vm_page_cowfault()
 305                          * removes the page from the backing object,
 306                          * which is not what we want.
 307                          */
 308                         vm_page_lock_queues();
 309                         if ((fs.m->cow) &&
 310                             (fault_type & VM_PROT_WRITE) &&
 311                             (fs.object == fs.first_object)) {
 312                                 vm_page_cowfault(fs.m);
 313                                 vm_page_unlock_queues();
 314                                 unlock_and_deallocate(&fs);
 315                                 goto RetryFault;
 316                         }
 317
 318                         /*
 319                          * Wait/Retry if the page is busy.  We have to do this
 320                          * if the page is busy via either VPO_BUSY or
 321                          * vm_page_t->busy because the vm_pager may be using
 322                          * vm_page_t->busy for pageouts ( and even pageins if
 323                          * it is the vnode pager ), and we could end up trying
 324                          * to pagein and pageout the same page simultaneously.
 325                          *
 326                          * We can theoretically allow the busy case on a read
 327                          * fault if the page is marked valid, but since such
 328                          * pages are typically already pmap'd, putting that
 329                          * special case in might be more effort then it is
 330                          * worth.  We cannot under any circumstances mess
 331                          * around with a vm_page_t->busy page except, perhaps,
 332                          * to pmap it.
 333                          */
 334                         if ((fs.m->oflags & VPO_BUSY) || fs.m->busy) {
 335                                 vm_page_unlock_queues();
 336                                 VM_OBJECT_UNLOCK(fs.object);
 337                                 if (fs.object != fs.first_object) {
 338                                         VM_OBJECT_LOCK(fs.first_object);
 339                                         vm_page_lock_queues();
 340                                         vm_page_free(fs.first_m);
 341                                         vm_page_unlock_queues();
 342                                         vm_object_pip_wakeup(fs.first_object);
 343                                         VM_OBJECT_UNLOCK(fs.first_object);
 344                                         fs.first_m = NULL;
 345                                 }
 346                                 unlock_map(&fs);
 347                                 VM_OBJECT_LOCK(fs.object);
 348                                 if (fs.m == vm_page_lookup(fs.object,
 349                                     fs.pindex)) {
 350                                         vm_page_sleep_if_busy(fs.m, TRUE,
 351                                             "vmpfw");
 352                                 }
 353                                 vm_object_pip_wakeup(fs.object);
 354                                 VM_OBJECT_UNLOCK(fs.object);
 355                                 PCPU_INC(cnt.v_intrans);
 356                                 vm_object_deallocate(fs.first_object);
 357                                 goto RetryFault;
 358                         }
 359                         vm_pageq_remove(fs.m);
 360                         vm_page_unlock_queues();
 361
 362                         /*
 363                          * Mark page busy for other processes, and the
 364                          * pagedaemon.  If it still isn't completely valid
 365                          * (readable), jump to readrest, else break-out ( we
 366                          * found the page ).
 367                          */
 368                         vm_page_busy(fs.m);
 369                         if (fs.m->valid != VM_PAGE_BITS_ALL &&
 370                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
 371                                 goto readrest;
 372                         }
 373
 374                         break;
 375                 }
 376
 377                 /*
 378                  * Page is not resident, If this is the search termination
 379                  * or the pager might contain the page, allocate a new page.
 380                  */
 381                 if (TRYPAGER || fs.object == fs.first_object) {
 382                         if (fs.pindex >= fs.object->size) {
 383                                 unlock_and_deallocate(&fs);
 384                                 return (KERN_PROTECTION_FAILURE);
 385                         }
 386
 387                         /*
 388                          * Allocate a new page for this object/offset pair.
 389                          */
 390                         fs.m = NULL;
 391                         if (!vm_page_count_severe()) {
 392 #if VM_NRESERVLEVEL > 0
 393                                 if ((fs.object->flags & OBJ_COLORED) == 0) {
 394                                         fs.object->flags |= OBJ_COLORED;
 395                                         fs.object->pg_color = atop(vaddr) -
 396                                             fs.pindex;
 397                                 }
 398 #endif
 399                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 400                                     (fs.object->type == OBJT_VNODE ||
 401                                      fs.object->backing_object != NULL) ?
 402                                     VM_ALLOC_NORMAL : VM_ALLOC_ZERO);
 403                         }
 404                         if (fs.m == NULL) {
 405                                 unlock_and_deallocate(&fs);
 406                                 VM_WAITPFAULT;
 407                                 goto RetryFault;
 408                         } else if (fs.m->valid == VM_PAGE_BITS_ALL)
 409                                 break;
 410                 }
 411
 412 readrest:
 413                 /*
 414                  * We have found a valid page or we have allocated a new page.
 415                  * The page thus may not be valid or may not be entirely
 416                  * valid.
 417                  *
 418                  * Attempt to fault-in the page if there is a chance that the
 419                  * pager has it, and potentially fault in additional pages
 420                  * at the same time.
 421                  */
 422                 if (TRYPAGER) {
 423                         int rv;
 424                         int reqpage = 0;
 425                         u_char behavior = vm_map_entry_behavior(fs.entry);
 426
 427                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 428                                 ahead = 0;
 429                                 behind = 0;
 430                         } else {
 431                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
 432                                 if (behind > VM_FAULT_READ_BEHIND)
 433                                         behind = VM_FAULT_READ_BEHIND;
 434
 435                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
 436                                 if (ahead > VM_FAULT_READ_AHEAD)
 437                                         ahead = VM_FAULT_READ_AHEAD;
 438                         }
 439                         is_first_object_locked = FALSE;
 440                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
 441                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
 442                               fs.pindex >= fs.entry->lastr &&
 443                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
 444                             (fs.first_object == fs.object ||
 445                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
 446                             fs.first_object->type != OBJT_DEVICE &&
 447                             fs.first_object->type != OBJT_PHYS &&
 448                             fs.first_object->type != OBJT_SG) {
 449                                 vm_pindex_t firstpindex, tmppindex;
 450
 451                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
 452                                         firstpindex = 0;
 453                                 else
 454                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
 455
 456                                 are_queues_locked = FALSE;
 457                                 /*
 458                                  * note: partially valid pages cannot be
 459                                  * included in the lookahead - NFS piecemeal
 460                                  * writes will barf on it badly.
 461                                  */
 462                                 for (tmppindex = fs.first_pindex - 1;
 463                                         tmppindex >= firstpindex;
 464                                         --tmppindex) {
 465                                         vm_page_t mt;
 466
 467                                         mt = vm_page_lookup(fs.first_object, tmppindex);
 468                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
 469                                                 break;
 470                                         if (mt->busy ||
 471                                             (mt->oflags & VPO_BUSY))
 472                                                 continue;
 473                                         if (!are_queues_locked) {
 474                                                 are_queues_locked = TRUE;
 475                                                 vm_page_lock_queues();
 476                                         }
 477                                         if (mt->hold_count ||
 478                                                 mt->wire_count)
 479                                                 continue;
 480                                         pmap_remove_all(mt);
 481                                         if (mt->dirty) {
 482                                                 vm_page_deactivate(mt);
 483                                         } else {
 484                                                 vm_page_cache(mt);
 485                                         }
 486                                 }
 487                                 if (are_queues_locked)
 488                                         vm_page_unlock_queues();
 489                                 ahead += behind;
 490                                 behind = 0;
 491                         }
 492                         if (is_first_object_locked)
 493                                 VM_OBJECT_UNLOCK(fs.first_object);
 494
 495                         /*
 496                          * Call the pager to retrieve the data, if any, after
 497                          * releasing the lock on the map.  We hold a ref on
 498                          * fs.object and the pages are VPO_BUSY'd.
 499                          */
 500                         unlock_map(&fs);
 501
 502 vnode_lock:
 503                         if (fs.object->type == OBJT_VNODE) {
 504                                 vp = fs.object->handle;
 505                                 if (vp == fs.vp)
 506                                         goto vnode_locked;
 507                                 else if (fs.vp != NULL) {
 508                                         vput(fs.vp);
 509                                         fs.vp = NULL;
 510                                 }
 511                                 locked = VOP_ISLOCKED(vp);
 512
 513                                 if (VFS_NEEDSGIANT(vp->v_mount) && !fs.vfslocked) {
 514                                         fs.vfslocked = 1;
 515                                         if (!mtx_trylock(&Giant)) {
 516                                                 VM_OBJECT_UNLOCK(fs.object);
 517                                                 mtx_lock(&Giant);
 518                                                 VM_OBJECT_LOCK(fs.object);
 519                                                 goto vnode_lock;
 520                                         }
 521                                 }
 522                                 if (locked != LK_EXCLUSIVE)
 523                                         locked = LK_SHARED;
 524                                 /* Do not sleep for vnode lock while fs.m is busy */
 525                                 error = vget(vp, locked | LK_CANRECURSE |
 526                                     LK_NOWAIT, curthread);
 527                                 if (error != 0) {
 528                                         int vfslocked;
 529
 530                                         vfslocked = fs.vfslocked;
 531                                         fs.vfslocked = 0; /* Keep Giant */
 532                                         vhold(vp);
 533                                         release_page(&fs);
 534                                         unlock_and_deallocate(&fs);
 535                                         error = vget(vp, locked | LK_RETRY |
 536                                             LK_CANRECURSE, curthread);
 537                                         vdrop(vp);
 538                                         fs.vp = vp;
 539                                         fs.vfslocked = vfslocked;
 540                                         KASSERT(error == 0,
 541                                             ("vm_fault: vget failed"));
 542                                         goto RetryFault;
 543                                 }
 544                                 fs.vp = vp;
 545                         }
 546 vnode_locked:
 547                         KASSERT(fs.vp == NULL || !fs.map->system_map,
 548                             ("vm_fault: vnode-backed object mapped by system map"));
 549
 550                         /*
 551                          * now we find out if any other pages should be paged
 552                          * in at this time this routine checks to see if the
 553                          * pages surrounding this fault reside in the same
 554                          * object as the page for this fault.  If they do,
 555                          * then they are faulted in also into the object.  The
 556                          * array "marray" returned contains an array of
 557                          * vm_page_t structs where one of them is the
 558                          * vm_page_t passed to the routine.  The reqpage
 559                          * return value is the index into the marray for the
 560                          * vm_page_t passed to the routine.
 561                          *
 562                          * fs.m plus the additional pages are VPO_BUSY'd.
 563                          */
 564                         faultcount = vm_fault_additional_pages(
 565                             fs.m, behind, ahead, marray, &reqpage);
 566
 567                         rv = faultcount ?
 568                             vm_pager_get_pages(fs.object, marray, faultcount,
 569                                 reqpage) : VM_PAGER_FAIL;
 570
 571                         if (rv == VM_PAGER_OK) {
 572                                 /*
 573                                  * Found the page. Leave it busy while we play
 574                                  * with it.
 575                                  */
 576
 577                                 /*
 578                                  * Relookup in case pager changed page. Pager
 579                                  * is responsible for disposition of old page
 580                                  * if moved.
 581                                  */
 582                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 583                                 if (!fs.m) {
 584                                         unlock_and_deallocate(&fs);
 585                                         goto RetryFault;
 586                                 }
 587
 588                                 hardfault++;
 589                                 break; /* break to PAGE HAS BEEN FOUND */
 590                         }
 591                         /*
 592                          * Remove the bogus page (which does not exist at this
 593                          * object/offset); before doing so, we must get back
 594                          * our object lock to preserve our invariant.
 595                          *
 596                          * Also wake up any other process that may want to bring
 597                          * in this page.
 598                          *
 599                          * If this is the top-level object, we must leave the
 600                          * busy page to prevent another process from rushing
 601                          * past us, and inserting the page in that object at
 602                          * the same time that we are.
 603                          */
 604                         if (rv == VM_PAGER_ERROR)
 605                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 606                                     curproc->p_pid, curproc->p_comm);
 607                         /*
 608                          * Data outside the range of the pager or an I/O error
 609                          */
 610                         /*
 611                          * XXX - the check for kernel_map is a kludge to work
 612                          * around having the machine panic on a kernel space
 613                          * fault w/ I/O error.
 614                          */
 615                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
 616                                 (rv == VM_PAGER_BAD)) {
 617                                 vm_page_lock_queues();
 618                                 vm_page_free(fs.m);
 619                                 vm_page_unlock_queues();
 620                                 fs.m = NULL;
 621                                 unlock_and_deallocate(&fs);
 622                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
 623                         }
 624                         if (fs.object != fs.first_object) {
 625                                 vm_page_lock_queues();
 626                                 vm_page_free(fs.m);
 627                                 vm_page_unlock_queues();
 628                                 fs.m = NULL;
 629                                 /*
 630                                  * XXX - we cannot just fall out at this
 631                                  * point, m has been freed and is invalid!
 632                                  */
 633                         }
 634                 }
 635
 636                 /*
 637                  * We get here if the object has default pager (or unwiring)
 638                  * or the pager doesn't have the page.
 639                  */
 640                 if (fs.object == fs.first_object)
 641                         fs.first_m = fs.m;
 642
 643                 /*
 644                  * Move on to the next object.  Lock the next object before
 645                  * unlocking the current one.
 646                  */
 647                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
 648                 next_object = fs.object->backing_object;
 649                 if (next_object == NULL) {
 650                         /*
 651                          * If there's no object left, fill the page in the top
 652                          * object with zeros.
 653                          */
 654                         if (fs.object != fs.first_object) {
 655                                 vm_object_pip_wakeup(fs.object);
 656                                 VM_OBJECT_UNLOCK(fs.object);
 657
 658                                 fs.object = fs.first_object;
 659                                 fs.pindex = fs.first_pindex;
 660                                 fs.m = fs.first_m;
 661                                 VM_OBJECT_LOCK(fs.object);
 662                         }
 663                         fs.first_m = NULL;
 664
 665                         /*
 666                          * Zero the page if necessary and mark it valid.
 667                          */
 668                         if ((fs.m->flags & PG_ZERO) == 0) {
 669                                 pmap_zero_page(fs.m);
 670                         } else {
 671                                 PCPU_INC(cnt.v_ozfod);
 672                         }
 673                         PCPU_INC(cnt.v_zfod);
 674                         fs.m->valid = VM_PAGE_BITS_ALL;
 675                         break;  /* break to PAGE HAS BEEN FOUND */
 676                 } else {
 677                         KASSERT(fs.object != next_object,
 678                             ("object loop %p", next_object));
 679                         VM_OBJECT_LOCK(next_object);
 680                         vm_object_pip_add(next_object, 1);
 681                         if (fs.object != fs.first_object)
 682                                 vm_object_pip_wakeup(fs.object);
 683                         VM_OBJECT_UNLOCK(fs.object);
 684                         fs.object = next_object;
 685                 }
 686         }
 687
 688         KASSERT((fs.m->oflags & VPO_BUSY) != 0,
 689             ("vm_fault: not busy after main loop"));
 690
 691         /*
 692          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
 693          * is held.]
 694          */
 695
 696         /*
 697          * If the page is being written, but isn't already owned by the
 698          * top-level object, we have to copy it into a new page owned by the
 699          * top-level object.
 700          */
 701         if (fs.object != fs.first_object) {
 702                 /*
 703                  * We only really need to copy if we want to write it.
 704                  */
 705                 if ((fault_type & (VM_PROT_COPY | VM_PROT_WRITE)) != 0) {
 706                         /*
 707                          * This allows pages to be virtually copied from a
 708                          * backing_object into the first_object, where the
 709                          * backing object has no other refs to it, and cannot
 710                          * gain any more refs.  Instead of a bcopy, we just
 711                          * move the page from the backing object to the
 712                          * first object.  Note that we must mark the page
 713                          * dirty in the first object so that it will go out
 714                          * to swap when needed.
 715                          */
 716                         is_first_object_locked = FALSE;
 717                         if (
 718                                 /*
 719                                  * Only one shadow object
 720                                  */
 721                                 (fs.object->shadow_count == 1) &&
 722                                 /*
 723                                  * No COW refs, except us
 724                                  */
 725                                 (fs.object->ref_count == 1) &&
 726                                 /*
 727                                  * No one else can look this object up
 728                                  */
 729                                 (fs.object->handle == NULL) &&
 730                                 /*
 731                                  * No other ways to look the object up
 732                                  */
 733                                 ((fs.object->type == OBJT_DEFAULT) ||
 734                                  (fs.object->type == OBJT_SWAP)) &&
 735                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
 736                                 /*
 737                                  * We don't chase down the shadow chain
 738                                  */
 739                             fs.object == fs.first_object->backing_object) {
 740                                 vm_page_lock_queues();
 741                                 /*
 742                                  * get rid of the unnecessary page
 743                                  */
 744                                 vm_page_free(fs.first_m);
 745                                 /*
 746                                  * grab the page and put it into the
 747                                  * process'es object.  The page is
 748                                  * automatically made dirty.
 749                                  */
 750                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
 751                                 vm_page_unlock_queues();
 752                                 vm_page_busy(fs.m);
 753                                 fs.first_m = fs.m;
 754                                 fs.m = NULL;
 755                                 PCPU_INC(cnt.v_cow_optim);
 756                         } else {
 757                                 /*
 758                                  * Oh, well, lets copy it.
 759                                  */
 760                                 pmap_copy_page(fs.m, fs.first_m);
 761                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
 762                                 if (wired && (fault_flags &
 763                                     VM_FAULT_CHANGE_WIRING) == 0) {
 764                                         vm_page_lock_queues();
 765                                         vm_page_wire(fs.first_m);
 766                                         vm_page_unwire(fs.m, FALSE);
 767                                         vm_page_unlock_queues();
 768                                 }
 769                                 /*
 770                                  * We no longer need the old page or object.
 771                                  */
 772                                 release_page(&fs);
 773                         }
 774                         /*
 775                          * fs.object != fs.first_object due to above
 776                          * conditional
 777                          */
 778                         vm_object_pip_wakeup(fs.object);
 779                         VM_OBJECT_UNLOCK(fs.object);
 780                         /*
 781                          * Only use the new page below...
 782                          */
 783                         fs.object = fs.first_object;
 784                         fs.pindex = fs.first_pindex;
 785                         fs.m = fs.first_m;
 786                         if (!is_first_object_locked)
 787                                 VM_OBJECT_LOCK(fs.object);
 788                         PCPU_INC(cnt.v_cow_faults);
 789                 } else {
 790                         prot &= ~VM_PROT_WRITE;
 791                 }
 792         }
 793
 794         /*
 795          * We must verify that the maps have not changed since our last
 796          * lookup.
 797          */
 798         if (!fs.lookup_still_valid) {
 799                 vm_object_t retry_object;
 800                 vm_pindex_t retry_pindex;
 801                 vm_prot_t retry_prot;
 802
 803                 if (!vm_map_trylock_read(fs.map)) {
 804                         release_page(&fs);
 805                         unlock_and_deallocate(&fs);
 806                         goto RetryFault;
 807                 }
 808                 fs.lookup_still_valid = TRUE;
 809                 if (fs.map->timestamp != map_generation) {
 810                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
 811                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
 812
 813                         /*
 814                          * If we don't need the page any longer, put it on the inactive
 815                          * list (the easiest thing to do here).  If no one needs it,
 816                          * pageout will grab it eventually.
 817                          */
 818                         if (result != KERN_SUCCESS) {
 819                                 release_page(&fs);
 820                                 unlock_and_deallocate(&fs);
 821
 822                                 /*
 823                                  * If retry of map lookup would have blocked then
 824                                  * retry fault from start.
 825                                  */
 826                                 if (result == KERN_FAILURE)
 827                                         goto RetryFault;
 828                                 return (result);
 829                         }
 830                         if ((retry_object != fs.first_object) ||
 831                             (retry_pindex != fs.first_pindex)) {
 832                                 release_page(&fs);
 833                                 unlock_and_deallocate(&fs);
 834                                 goto RetryFault;
 835                         }
 836
 837                         /*
 838                          * Check whether the protection has changed or the object has
 839                          * been copied while we left the map unlocked. Changing from
 840                          * read to write permission is OK - we leave the page
 841                          * write-protected, and catch the write fault. Changing from
 842                          * write to read permission means that we can't mark the page
 843                          * write-enabled after all.
 844                          */
 845                         prot &= retry_prot;
 846                 }
 847         }
 848         /*
 849          * If the page was filled by a pager, update the map entry's
 850          * last read offset.  Since the pager does not return the
 851          * actual set of pages that it read, this update is based on
 852          * the requested set.  Typically, the requested and actual
 853          * sets are the same.
 854          *
 855          * XXX The following assignment modifies the map
 856          * without holding a write lock on it.
 857          */
 858         if (hardfault)
 859                 fs.entry->lastr = fs.pindex + faultcount - behind;
 860
 861         if (prot & VM_PROT_WRITE) {
 862                 vm_object_set_writeable_dirty(fs.object);
 863
 864                 /*
 865                  * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
 866                  * if the page is already dirty to prevent data written with
 867                  * the expectation of being synced from not being synced.
 868                  * Likewise if this entry does not request NOSYNC then make
 869                  * sure the page isn't marked NOSYNC.  Applications sharing
 870                  * data should use the same flags to avoid ping ponging.
 871                  */
 872                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
 873                         if (fs.m->dirty == 0)
 874                                 fs.m->oflags |= VPO_NOSYNC;
 875                 } else {
 876                         fs.m->oflags &= ~VPO_NOSYNC;
 877                 }
 878
 879                 /*
 880                  * If the fault is a write, we know that this page is being
 881                  * written NOW so dirty it explicitly to save on
 882                  * pmap_is_modified() calls later.
 883                  *
 884                  * Also tell the backing pager, if any, that it should remove
 885                  * any swap backing since the page is now dirty.
 886                  */
 887                 if ((fault_type & VM_PROT_WRITE) != 0 &&
 888                     (fault_flags & VM_FAULT_CHANGE_WIRING) == 0) {
 889                         vm_page_dirty(fs.m);
 890                         vm_pager_page_unswapped(fs.m);
 891                 }
 892         }
 893
 894         /*
 895          * Page had better still be busy
 896          */
 897         KASSERT(fs.m->oflags & VPO_BUSY,
 898                 ("vm_fault: page %p not busy!", fs.m));
 899         /*
 900          * Page must be completely valid or it is not fit to
 901          * map into user space.  vm_pager_get_pages() ensures this.
 902          */
 903         KASSERT(fs.m->valid == VM_PAGE_BITS_ALL,
 904             ("vm_fault: page %p partially invalid", fs.m));
 905         VM_OBJECT_UNLOCK(fs.object);
 906
 907         /*
 908          * Put this page into the physical map.  We had to do the unlock above
 909          * because pmap_enter() may sleep.  We don't put the page
 910          * back on the active queue until later so that the pageout daemon
 911          * won't find it (yet).
 912          */
 913         pmap_enter(fs.map->pmap, vaddr, fault_type, fs.m, prot, wired);
 914         if ((fault_flags & VM_FAULT_CHANGE_WIRING) == 0 && wired == 0)
 915                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
 916         VM_OBJECT_LOCK(fs.object);
 917         vm_page_lock_queues();
 918         vm_page_flag_set(fs.m, PG_REFERENCED);
 919
 920         /*
 921          * If the page is not wired down, then put it where the pageout daemon
 922          * can find it.
 923          */
 924         if (fault_flags & VM_FAULT_CHANGE_WIRING) {
 925                 if (wired)
 926                         vm_page_wire(fs.m);
 927                 else
 928                         vm_page_unwire(fs.m, 1);
 929         } else {
 930                 vm_page_activate(fs.m);
 931         }
 932         vm_page_unlock_queues();
 933         vm_page_wakeup(fs.m);
 934
 935         /*
 936          * Unlock everything, and return
 937          */
 938         unlock_and_deallocate(&fs);
 939         if (hardfault)
 940                 curthread->td_ru.ru_majflt++;
 941         else
 942                 curthread->td_ru.ru_minflt++;
 943
 944         return (KERN_SUCCESS);
 945 }
 946
 947 /*
 948  * vm_fault_prefault provides a quick way of clustering
 949  * pagefaults into a processes address space.  It is a "cousin"
 950  * of vm_map_pmap_enter, except it runs at page fault time instead
 951  * of mmap time.
 952  */
 953 static void
 954 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
 955 {
 956         int i;
 957         vm_offset_t addr, starta;
 958         vm_pindex_t pindex;
 959         vm_page_t m;
 960         vm_object_t object;
 961
 962         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
 963                 return;
 964
 965         object = entry->object.vm_object;
 966
 967         starta = addra - PFBAK * PAGE_SIZE;
 968         if (starta < entry->start) {
 969                 starta = entry->start;
 970         } else if (starta > addra) {
 971                 starta = 0;
 972         }
 973
 974         for (i = 0; i < PAGEORDER_SIZE; i++) {
 975                 vm_object_t backing_object, lobject;
 976
 977                 addr = addra + prefault_pageorder[i];
 978                 if (addr > addra + (PFFOR * PAGE_SIZE))
 979                         addr = 0;
 980
 981                 if (addr < starta || addr >= entry->end)
 982                         continue;
 983
 984                 if (!pmap_is_prefaultable(pmap, addr))
 985                         continue;
 986
 987                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
 988                 lobject = object;
 989                 VM_OBJECT_LOCK(lobject);
 990                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
 991                     lobject->type == OBJT_DEFAULT &&
 992                     (backing_object = lobject->backing_object) != NULL) {
 993                         KASSERT((lobject->backing_object_offset & PAGE_MASK) ==
 994                             0, ("vm_fault_prefault: unaligned object offset"));
 995                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
 996                         VM_OBJECT_LOCK(backing_object);
 997                         VM_OBJECT_UNLOCK(lobject);
 998                         lobject = backing_object;
 999                 }
1000                 /*
1001                  * give-up when a page is not in memory
1002                  */
1003                 if (m == NULL) {
1004                         VM_OBJECT_UNLOCK(lobject);
1005                         break;
1006                 }
1007                 if (m->valid == VM_PAGE_BITS_ALL &&
1008                     (m->flags & PG_FICTITIOUS) == 0) {
1009                         vm_page_lock_queues();
1010                         pmap_enter_quick(pmap, addr, m, entry->protection);
1011                         vm_page_unlock_queues();
1012                 }
1013                 VM_OBJECT_UNLOCK(lobject);
1014         }
1015 }
1016
1017 /*
1018  *      vm_fault_quick:
1019  *
1020  *      Ensure that the requested virtual address, which may be in userland,
1021  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
1022  */
1023 int
1024 vm_fault_quick(caddr_t v, int prot)
1025 {
1026         int r;
1027
1028         if (prot & VM_PROT_WRITE)
1029                 r = subyte(v, fubyte(v));
1030         else
1031                 r = fubyte(v);
1032         return(r);
1033 }
1034
1035 /*
1036  *      vm_fault_wire:
1037  *
1038  *      Wire down a range of virtual addresses in a map.
1039  */
1040 int
1041 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1042     boolean_t fictitious)
1043 {
1044         vm_offset_t va;
1045         int rv;
1046
1047         /*
1048          * We simulate a fault to get the page and enter it in the physical
1049          * map.  For user wiring, we only ask for read access on currently
1050          * read-only sections.
1051          */
1052         for (va = start; va < end; va += PAGE_SIZE) {
1053                 rv = vm_fault(map, va, VM_PROT_NONE, 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  *              Create new shadow object backing dst_entry with private copy of
1100  *              all underlying pages. When src_entry is equal to dst_entry,
1101  *              function implements COW for wired-down map entry. Otherwise,
1102  *              it forks wired entry into dst_map.
1103  *
1104  *      In/out conditions:
1105  *              The source and destination maps must be locked for write.
1106  *              The source map entry must be wired down (or be a sharing map
1107  *              entry corresponding to a main map entry that is wired down).
1108  */
1109 void
1110 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1111     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
1112     vm_ooffset_t *fork_charge)
1113 {
1114         vm_object_t backing_object, dst_object, object, src_object;
1115         vm_pindex_t dst_pindex, pindex, src_pindex;
1116         vm_prot_t access, prot;
1117         vm_offset_t vaddr;
1118         vm_page_t dst_m;
1119         vm_page_t src_m;
1120         boolean_t src_readonly, upgrade;
1121
1122 #ifdef  lint
1123         src_map++;
1124 #endif  /* lint */
1125
1126         upgrade = src_entry == dst_entry;
1127
1128         src_object = src_entry->object.vm_object;
1129         src_pindex = OFF_TO_IDX(src_entry->offset);
1130         src_readonly = (src_entry->protection & VM_PROT_WRITE) == 0;
1131
1132         /*
1133          * Create the top-level object for the destination entry. (Doesn't
1134          * actually shadow anything - we copy the pages directly.)
1135          */
1136         dst_object = vm_object_allocate(OBJT_DEFAULT,
1137             OFF_TO_IDX(dst_entry->end - dst_entry->start));
1138 #if VM_NRESERVLEVEL > 0
1139         dst_object->flags |= OBJ_COLORED;
1140         dst_object->pg_color = atop(dst_entry->start);
1141 #endif
1142
1143         VM_OBJECT_LOCK(dst_object);
1144         KASSERT(upgrade || dst_entry->object.vm_object == NULL,
1145             ("vm_fault_copy_entry: vm_object not NULL"));
1146         dst_entry->object.vm_object = dst_object;
1147         dst_entry->offset = 0;
1148         dst_object->charge = dst_entry->end - dst_entry->start;
1149         if (fork_charge != NULL) {
1150                 KASSERT(dst_entry->uip == NULL,
1151                     ("vm_fault_copy_entry: leaked swp charge"));
1152                 dst_object->uip = curthread->td_ucred->cr_ruidinfo;
1153                 uihold(dst_object->uip);
1154                 *fork_charge += dst_object->charge;
1155         } else {
1156                 dst_object->uip = dst_entry->uip;
1157                 dst_entry->uip = NULL;
1158         }
1159         access = prot = dst_entry->protection;
1160         /*
1161          * If not an upgrade, then enter the mappings in the pmap as
1162          * read and/or execute accesses.  Otherwise, enter them as
1163          * write accesses.
1164          *
1165          * A writeable large page mapping is only created if all of
1166          * the constituent small page mappings are modified. Marking
1167          * PTEs as modified on inception allows promotion to happen
1168          * without taking potentially large number of soft faults.
1169          */
1170         if (!upgrade)
1171                 access &= ~VM_PROT_WRITE;
1172
1173         /*
1174          * Loop through all of the pages in the entry's range, copying each
1175          * one from the source object (it should be there) to the destination
1176          * object.
1177          */
1178         for (vaddr = dst_entry->start, dst_pindex = 0;
1179             vaddr < dst_entry->end;
1180             vaddr += PAGE_SIZE, dst_pindex++) {
1181
1182                 /*
1183                  * Allocate a page in the destination object.
1184                  */
1185                 do {
1186                         dst_m = vm_page_alloc(dst_object, dst_pindex,
1187                             VM_ALLOC_NORMAL);
1188                         if (dst_m == NULL) {
1189                                 VM_OBJECT_UNLOCK(dst_object);
1190                                 VM_WAIT;
1191                                 VM_OBJECT_LOCK(dst_object);
1192                         }
1193                 } while (dst_m == NULL);
1194
1195                 /*
1196                  * Find the page in the source object, and copy it in.
1197                  * (Because the source is wired down, the page will be in
1198                  * memory.)
1199                  */
1200                 VM_OBJECT_LOCK(src_object);
1201                 object = src_object;
1202                 pindex = src_pindex + dst_pindex;
1203                 while ((src_m = vm_page_lookup(object, pindex)) == NULL &&
1204                     src_readonly &&
1205                     (backing_object = object->backing_object) != NULL) {
1206                         /*
1207                          * Allow fallback to backing objects if we are reading.
1208                          */
1209                         VM_OBJECT_LOCK(backing_object);
1210                         pindex += OFF_TO_IDX(object->backing_object_offset);
1211                         VM_OBJECT_UNLOCK(object);
1212                         object = backing_object;
1213                 }
1214                 if (src_m == NULL)
1215                         panic("vm_fault_copy_wired: page missing");
1216                 pmap_copy_page(src_m, dst_m);
1217                 VM_OBJECT_UNLOCK(object);
1218                 dst_m->valid = VM_PAGE_BITS_ALL;
1219                 VM_OBJECT_UNLOCK(dst_object);
1220
1221                 /*
1222                  * Enter it in the pmap. If a wired, copy-on-write
1223                  * mapping is being replaced by a write-enabled
1224                  * mapping, then wire that new mapping.
1225                  */
1226                 pmap_enter(dst_map->pmap, vaddr, access, dst_m, prot, upgrade);
1227
1228                 /*
1229                  * Mark it no longer busy, and put it on the active list.
1230                  */
1231                 VM_OBJECT_LOCK(dst_object);
1232                 vm_page_lock_queues();
1233                 if (upgrade) {
1234                         vm_page_unwire(src_m, 0);
1235                         vm_page_wire(dst_m);
1236                 } else
1237                         vm_page_activate(dst_m);
1238                 vm_page_unlock_queues();
1239                 vm_page_wakeup(dst_m);
1240         }
1241         VM_OBJECT_UNLOCK(dst_object);
1242         if (upgrade) {
1243                 dst_entry->eflags &= ~(MAP_ENTRY_COW | MAP_ENTRY_NEEDS_COPY);
1244                 vm_object_deallocate(src_object);
1245         }
1246 }
1247
1248
1249 /*
1250  * This routine checks around the requested page for other pages that
1251  * might be able to be faulted in.  This routine brackets the viable
1252  * pages for the pages to be paged in.
1253  *
1254  * Inputs:
1255  *      m, rbehind, rahead
1256  *
1257  * Outputs:
1258  *  marray (array of vm_page_t), reqpage (index of requested page)
1259  *
1260  * Return value:
1261  *  number of pages in marray
1262  */
1263 static int
1264 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
1265         vm_page_t m;
1266         int rbehind;
1267         int rahead;
1268         vm_page_t *marray;
1269         int *reqpage;
1270 {
1271         int i,j;
1272         vm_object_t object;
1273         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1274         vm_page_t rtm;
1275         int cbehind, cahead;
1276
1277         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
1278
1279         object = m->object;
1280         pindex = m->pindex;
1281         cbehind = cahead = 0;
1282
1283         /*
1284          * if the requested page is not available, then give up now
1285          */
1286         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1287                 return 0;
1288         }
1289
1290         if ((cbehind == 0) && (cahead == 0)) {
1291                 *reqpage = 0;
1292                 marray[0] = m;
1293                 return 1;
1294         }
1295
1296         if (rahead > cahead) {
1297                 rahead = cahead;
1298         }
1299
1300         if (rbehind > cbehind) {
1301                 rbehind = cbehind;
1302         }
1303
1304         /*
1305          * scan backward for the read behind pages -- in memory
1306          */
1307         if (pindex > 0) {
1308                 if (rbehind > pindex) {
1309                         rbehind = pindex;
1310                         startpindex = 0;
1311                 } else {
1312                         startpindex = pindex - rbehind;
1313                 }
1314
1315                 if ((rtm = TAILQ_PREV(m, pglist, listq)) != NULL &&
1316                     rtm->pindex >= startpindex)
1317                         startpindex = rtm->pindex + 1;
1318
1319                 /* tpindex is unsigned; beware of numeric underflow. */
1320                 for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
1321                     tpindex < pindex; i++, tpindex--) {
1322
1323                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
1324                             VM_ALLOC_IFNOTCACHED);
1325                         if (rtm == NULL) {
1326                                 /*
1327                                  * Shift the allocated pages to the
1328                                  * beginning of the array.
1329                                  */
1330                                 for (j = 0; j < i; j++) {
1331                                         marray[j] = marray[j + tpindex + 1 -
1332                                             startpindex];
1333                                 }
1334                                 break;
1335                         }
1336
1337                         marray[tpindex - startpindex] = rtm;
1338                 }
1339         } else {
1340                 startpindex = 0;
1341                 i = 0;
1342         }
1343
1344         marray[i] = m;
1345         /* page offset of the required page */
1346         *reqpage = i;
1347
1348         tpindex = pindex + 1;
1349         i++;
1350
1351         /*
1352          * scan forward for the read ahead pages
1353          */
1354         endpindex = tpindex + rahead;
1355         if ((rtm = TAILQ_NEXT(m, listq)) != NULL && rtm->pindex < endpindex)
1356                 endpindex = rtm->pindex;
1357         if (endpindex > object->size)
1358                 endpindex = object->size;
1359
1360         for (; tpindex < endpindex; i++, tpindex++) {
1361
1362                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
1363                     VM_ALLOC_IFNOTCACHED);
1364                 if (rtm == NULL) {
1365                         break;
1366                 }
1367
1368                 marray[i] = rtm;
1369         }
1370
1371         /* return number of pages */
1372         return i;
1373 }