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