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 <sys/param.h>
  78 #include <sys/systm.h>
  79 #include <sys/kernel.h>
  80 #include <sys/lock.h>
  81 #include <sys/mutex.h>
  82 #include <sys/proc.h>
  83 #include <sys/resourcevar.h>
  84 #include <sys/sysctl.h>
  85 #include <sys/vmmeter.h>
  86 #include <sys/vnode.h>
  87
  88 #include <vm/vm.h>
  89 #include <vm/vm_param.h>
  90 #include <vm/pmap.h>
  91 #include <vm/vm_map.h>
  92 #include <vm/vm_object.h>
  93 #include <vm/vm_page.h>
  94 #include <vm/vm_pageout.h>
  95 #include <vm/vm_kern.h>
  96 #include <vm/vm_pager.h>
  97 #include <vm/vnode_pager.h>
  98 #include <vm/vm_extern.h>
  99
 100 #include <sys/mount.h>  /* XXX Temporary for VFS_LOCK_GIANT() */
 101
 102 #define PFBAK 4
 103 #define PFFOR 4
 104 #define PAGEORDER_SIZE (PFBAK+PFFOR)
 105
 106 static int prefault_pageorder[] = {
 107         -1 * PAGE_SIZE, 1 * PAGE_SIZE,
 108         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
 109         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
 110         -4 * PAGE_SIZE, 4 * PAGE_SIZE
 111 };
 112
 113 static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
 114 static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
 115
 116 #define VM_FAULT_READ_AHEAD 8
 117 #define VM_FAULT_READ_BEHIND 7
 118 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
 119
 120 struct faultstate {
 121         vm_page_t m;
 122         vm_object_t object;
 123         vm_pindex_t pindex;
 124         vm_page_t first_m;
 125         vm_object_t     first_object;
 126         vm_pindex_t first_pindex;
 127         vm_map_t map;
 128         vm_map_entry_t entry;
 129         int lookup_still_valid;
 130         struct vnode *vp;
 131 };
 132
 133 static inline void
 134 release_page(struct faultstate *fs)
 135 {
 136         vm_page_lock_queues();
 137         vm_page_wakeup(fs->m);
 138         vm_page_deactivate(fs->m);
 139         vm_page_unlock_queues();
 140         fs->m = NULL;
 141 }
 142
 143 static inline void
 144 unlock_map(struct faultstate *fs)
 145 {
 146         if (fs->lookup_still_valid) {
 147                 vm_map_lookup_done(fs->map, fs->entry);
 148                 fs->lookup_still_valid = FALSE;
 149         }
 150 }
 151
 152 static void
 153 unlock_and_deallocate(struct faultstate *fs)
 154 {
 155         boolean_t firstobjneedgiant;
 156
 157         vm_object_pip_wakeup(fs->object);
 158         VM_OBJECT_UNLOCK(fs->object);
 159         if (fs->object != fs->first_object) {
 160                 VM_OBJECT_LOCK(fs->first_object);
 161                 vm_page_lock_queues();
 162                 vm_page_free(fs->first_m);
 163                 vm_page_unlock_queues();
 164                 vm_object_pip_wakeup(fs->first_object);
 165                 VM_OBJECT_UNLOCK(fs->first_object);
 166                 fs->first_m = NULL;
 167         }
 168         firstobjneedgiant = (fs->first_object->flags & OBJ_NEEDGIANT) != 0;
 169         vm_object_deallocate(fs->first_object);
 170         unlock_map(fs);
 171         if (fs->vp != NULL) {
 172                 int vfslocked;
 173
 174                 vfslocked = VFS_LOCK_GIANT(fs->vp->v_mount);
 175                 vput(fs->vp);
 176                 fs->vp = NULL;
 177                 VFS_UNLOCK_GIANT(vfslocked);
 178         }
 179         if (firstobjneedgiant)
 180                 VM_UNLOCK_GIANT();
 181 }
 182
 183 /*
 184  * TRYPAGER - used by vm_fault to calculate whether the pager for the
 185  *            current object *might* contain the page.
 186  *
 187  *            default objects are zero-fill, there is no real pager.
 188  */
 189 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
 190                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
 191
 192 /*
 193  *      vm_fault:
 194  *
 195  *      Handle a page fault occurring at the given address,
 196  *      requiring the given permissions, in the map specified.
 197  *      If successful, the page is inserted into the
 198  *      associated physical map.
 199  *
 200  *      NOTE: the given address should be truncated to the
 201  *      proper page address.
 202  *
 203  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 204  *      a standard error specifying why the fault is fatal is returned.
 205  *
 206  *
 207  *      The map in question must be referenced, and remains so.
 208  *      Caller may hold no locks.
 209  */
 210 int
 211 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 212          int fault_flags)
 213 {
 214         vm_prot_t prot;
 215         int is_first_object_locked, result;
 216         boolean_t growstack, wired;
 217         int map_generation;
 218         vm_object_t next_object;
 219         vm_page_t marray[VM_FAULT_READ];
 220         int hardfault;
 221         int faultcount;
 222         struct faultstate fs;
 223
 224         hardfault = 0;
 225         growstack = TRUE;
 226         atomic_add_int(&cnt.v_vm_faults, 1);
 227
 228 RetryFault:;
 229
 230         /*
 231          * Find the backing store object and offset into it to begin the
 232          * search.
 233          */
 234         fs.map = map;
 235         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
 236             &fs.first_object, &fs.first_pindex, &prot, &wired);
 237         if (result != KERN_SUCCESS) {
 238                 if (result != KERN_PROTECTION_FAILURE ||
 239                     (fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE) {
 240                         if (growstack && result == KERN_INVALID_ADDRESS &&
 241                             map != kernel_map && curproc != NULL) {
 242                                 result = vm_map_growstack(curproc, vaddr);
 243                                 if (result != KERN_SUCCESS)
 244                                         return (KERN_FAILURE);
 245                                 growstack = FALSE;
 246                                 goto RetryFault;
 247                         }
 248                         return (result);
 249                 }
 250
 251                 /*
 252                  * If we are user-wiring a r/w segment, and it is COW, then
 253                  * we need to do the COW operation.  Note that we don't COW
 254                  * currently RO sections now, because it is NOT desirable
 255                  * to COW .text.  We simply keep .text from ever being COW'ed
 256                  * and take the heat that one cannot debug wired .text sections.
 257                  */
 258                 result = vm_map_lookup(&fs.map, vaddr,
 259                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
 260                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
 261                 if (result != KERN_SUCCESS)
 262                         return (result);
 263
 264                 /*
 265                  * If we don't COW now, on a user wire, the user will never
 266                  * be able to write to the mapping.  If we don't make this
 267                  * restriction, the bookkeeping would be nearly impossible.
 268                  *
 269                  * XXX The following assignment modifies the map without
 270                  * holding a write lock on it.
 271                  */
 272                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
 273                         fs.entry->max_protection &= ~VM_PROT_WRITE;
 274         }
 275
 276         map_generation = fs.map->timestamp;
 277
 278         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 279                 panic("vm_fault: fault on nofault entry, addr: %lx",
 280                     (u_long)vaddr);
 281         }
 282
 283         /*
 284          * Make a reference to this object to prevent its disposal while we
 285          * are messing with it.  Once we have the reference, the map is free
 286          * to be diddled.  Since objects reference their shadows (and copies),
 287          * they will stay around as well.
 288          *
 289          * Bump the paging-in-progress count to prevent size changes (e.g.
 290          * truncation operations) during I/O.  This must be done after
 291          * obtaining the vnode lock in order to avoid possible deadlocks.
 292          *
 293          * XXX vnode_pager_lock() can block without releasing the map lock.
 294          */
 295         if (fs.first_object->flags & OBJ_NEEDGIANT)
 296                 mtx_lock(&Giant);
 297         VM_OBJECT_LOCK(fs.first_object);
 298         vm_object_reference_locked(fs.first_object);
 299         fs.vp = vnode_pager_lock(fs.first_object);
 300         KASSERT(fs.vp == NULL || !fs.map->system_map,
 301             ("vm_fault: vnode-backed object mapped by system map"));
 302         KASSERT((fs.first_object->flags & OBJ_NEEDGIANT) == 0 ||
 303             !fs.map->system_map,
 304             ("vm_fault: Object requiring giant mapped by system map"));
 305         if (fs.first_object->flags & OBJ_NEEDGIANT && debug_mpsafevm)
 306                 mtx_unlock(&Giant);
 307         vm_object_pip_add(fs.first_object, 1);
 308
 309         fs.lookup_still_valid = TRUE;
 310
 311         if (wired)
 312                 fault_type = prot;
 313
 314         fs.first_m = NULL;
 315
 316         /*
 317          * Search for the page at object/offset.
 318          */
 319         fs.object = fs.first_object;
 320         fs.pindex = fs.first_pindex;
 321         while (TRUE) {
 322                 /*
 323                  * If the object is dead, we stop here
 324                  */
 325                 if (fs.object->flags & OBJ_DEAD) {
 326                         unlock_and_deallocate(&fs);
 327                         return (KERN_PROTECTION_FAILURE);
 328                 }
 329
 330                 /*
 331                  * See if page is resident
 332                  */
 333                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 334                 if (fs.m != NULL) {
 335                         int queue;
 336
 337                         /*
 338                          * check for page-based copy on write.
 339                          * We check fs.object == fs.first_object so
 340                          * as to ensure the legacy COW mechanism is
 341                          * used when the page in question is part of
 342                          * a shadow object.  Otherwise, vm_page_cowfault()
 343                          * removes the page from the backing object,
 344                          * which is not what we want.
 345                          */
 346                         vm_page_lock_queues();
 347                         if ((fs.m->cow) &&
 348                             (fault_type & VM_PROT_WRITE) &&
 349                             (fs.object == fs.first_object)) {
 350                                 vm_page_cowfault(fs.m);
 351                                 vm_page_unlock_queues();
 352                                 unlock_and_deallocate(&fs);
 353                                 goto RetryFault;
 354                         }
 355
 356                         /*
 357                          * Wait/Retry if the page is busy.  We have to do this
 358                          * if the page is busy via either PG_BUSY or
 359                          * vm_page_t->busy because the vm_pager may be using
 360                          * vm_page_t->busy for pageouts ( and even pageins if
 361                          * it is the vnode pager ), and we could end up trying
 362                          * to pagein and pageout the same page simultaneously.
 363                          *
 364                          * We can theoretically allow the busy case on a read
 365                          * fault if the page is marked valid, but since such
 366                          * pages are typically already pmap'd, putting that
 367                          * special case in might be more effort then it is
 368                          * worth.  We cannot under any circumstances mess
 369                          * around with a vm_page_t->busy page except, perhaps,
 370                          * to pmap it.
 371                          */
 372                         if ((fs.m->flags & PG_BUSY) || fs.m->busy) {
 373                                 vm_page_unlock_queues();
 374                                 VM_OBJECT_UNLOCK(fs.object);
 375                                 if (fs.object != fs.first_object) {
 376                                         VM_OBJECT_LOCK(fs.first_object);
 377                                         vm_page_lock_queues();
 378                                         vm_page_free(fs.first_m);
 379                                         vm_page_unlock_queues();
 380                                         vm_object_pip_wakeup(fs.first_object);
 381                                         VM_OBJECT_UNLOCK(fs.first_object);
 382                                         fs.first_m = NULL;
 383                                 }
 384                                 unlock_map(&fs);
 385                                 if (fs.vp != NULL) {
 386                                         int vfslck;
 387
 388                                         vfslck = VFS_LOCK_GIANT(fs.vp->v_mount);
 389                                         vput(fs.vp);
 390                                         fs.vp = NULL;
 391                                         VFS_UNLOCK_GIANT(vfslck);
 392                                 }
 393                                 VM_OBJECT_LOCK(fs.object);
 394                                 if (fs.m == vm_page_lookup(fs.object,
 395                                     fs.pindex)) {
 396                                         vm_page_lock_queues();
 397                                         if (!vm_page_sleep_if_busy(fs.m, TRUE,
 398                                             "vmpfw"))
 399                                                 vm_page_unlock_queues();
 400                                 }
 401                                 vm_object_pip_wakeup(fs.object);
 402                                 VM_OBJECT_UNLOCK(fs.object);
 403                                 atomic_add_int(&cnt.v_intrans, 1);
 404                                 if (fs.first_object->flags & OBJ_NEEDGIANT)
 405                                         VM_UNLOCK_GIANT();
 406                                 vm_object_deallocate(fs.first_object);
 407                                 goto RetryFault;
 408                         }
 409                         queue = fs.m->queue;
 410
 411                         vm_pageq_remove_nowakeup(fs.m);
 412
 413                         if (VM_PAGE_RESOLVEQUEUE(fs.m, queue) == PQ_CACHE &&
 414                             vm_page_count_severe()) {
 415                                 vm_page_activate(fs.m);
 416                                 vm_page_unlock_queues();
 417                                 unlock_and_deallocate(&fs);
 418                                 VM_WAITPFAULT;
 419                                 goto RetryFault;
 420                         }
 421
 422                         /*
 423                          * Mark page busy for other processes, and the
 424                          * pagedaemon.  If it still isn't completely valid
 425                          * (readable), jump to readrest, else break-out ( we
 426                          * found the page ).
 427                          */
 428                         vm_page_busy(fs.m);
 429                         vm_page_unlock_queues();
 430                         if (((fs.m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) &&
 431                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
 432                                 goto readrest;
 433                         }
 434
 435                         break;
 436                 }
 437
 438                 /*
 439                  * Page is not resident, If this is the search termination
 440                  * or the pager might contain the page, allocate a new page.
 441                  */
 442                 if (TRYPAGER || fs.object == fs.first_object) {
 443                         if (fs.pindex >= fs.object->size) {
 444                                 unlock_and_deallocate(&fs);
 445                                 return (KERN_PROTECTION_FAILURE);
 446                         }
 447
 448                         /*
 449                          * Allocate a new page for this object/offset pair.
 450                          */
 451                         fs.m = NULL;
 452                         if (!vm_page_count_severe()) {
 453                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 454                                     (fs.vp || fs.object->backing_object)? VM_ALLOC_NORMAL: VM_ALLOC_ZERO);
 455                         }
 456                         if (fs.m == NULL) {
 457                                 unlock_and_deallocate(&fs);
 458                                 VM_WAITPFAULT;
 459                                 goto RetryFault;
 460                         }
 461                 }
 462
 463 readrest:
 464                 /*
 465                  * We have found a valid page or we have allocated a new page.
 466                  * The page thus may not be valid or may not be entirely
 467                  * valid.
 468                  *
 469                  * Attempt to fault-in the page if there is a chance that the
 470                  * pager has it, and potentially fault in additional pages
 471                  * at the same time.
 472                  */
 473                 if (TRYPAGER) {
 474                         int rv;
 475                         int reqpage;
 476                         int ahead, behind;
 477                         u_char behavior = vm_map_entry_behavior(fs.entry);
 478
 479                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 480                                 ahead = 0;
 481                                 behind = 0;
 482                         } else {
 483                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
 484                                 if (behind > VM_FAULT_READ_BEHIND)
 485                                         behind = VM_FAULT_READ_BEHIND;
 486
 487                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
 488                                 if (ahead > VM_FAULT_READ_AHEAD)
 489                                         ahead = VM_FAULT_READ_AHEAD;
 490                         }
 491                         is_first_object_locked = FALSE;
 492                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
 493                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
 494                               fs.pindex >= fs.entry->lastr &&
 495                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
 496                             (fs.first_object == fs.object ||
 497                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
 498                             fs.first_object->type != OBJT_DEVICE) {
 499                                 vm_pindex_t firstpindex, tmppindex;
 500
 501                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
 502                                         firstpindex = 0;
 503                                 else
 504                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
 505
 506                                 vm_page_lock_queues();
 507                                 /*
 508                                  * note: partially valid pages cannot be
 509                                  * included in the lookahead - NFS piecemeal
 510                                  * writes will barf on it badly.
 511                                  */
 512                                 for (tmppindex = fs.first_pindex - 1;
 513                                         tmppindex >= firstpindex;
 514                                         --tmppindex) {
 515                                         vm_page_t mt;
 516
 517                                         mt = vm_page_lookup(fs.first_object, tmppindex);
 518                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
 519                                                 break;
 520                                         if (mt->busy ||
 521                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
 522                                                 mt->hold_count ||
 523                                                 mt->wire_count)
 524                                                 continue;
 525                                         pmap_remove_all(mt);
 526                                         if (mt->dirty) {
 527                                                 vm_page_deactivate(mt);
 528                                         } else {
 529                                                 vm_page_cache(mt);
 530                                         }
 531                                 }
 532                                 vm_page_unlock_queues();
 533                                 ahead += behind;
 534                                 behind = 0;
 535                         }
 536                         if (is_first_object_locked)
 537                                 VM_OBJECT_UNLOCK(fs.first_object);
 538                         /*
 539                          * now we find out if any other pages should be paged
 540                          * in at this time this routine checks to see if the
 541                          * pages surrounding this fault reside in the same
 542                          * object as the page for this fault.  If they do,
 543                          * then they are faulted in also into the object.  The
 544                          * array "marray" returned contains an array of
 545                          * vm_page_t structs where one of them is the
 546                          * vm_page_t passed to the routine.  The reqpage
 547                          * return value is the index into the marray for the
 548                          * vm_page_t passed to the routine.
 549                          *
 550                          * fs.m plus the additional pages are PG_BUSY'd.
 551                          *
 552                          * XXX vm_fault_additional_pages() can block
 553                          * without releasing the map lock.
 554                          */
 555                         faultcount = vm_fault_additional_pages(
 556                             fs.m, behind, ahead, marray, &reqpage);
 557
 558                         /*
 559                          * update lastr imperfectly (we do not know how much
 560                          * getpages will actually read), but good enough.
 561                          *
 562                          * XXX The following assignment modifies the map
 563                          * without holding a write lock on it.
 564                          */
 565                         fs.entry->lastr = fs.pindex + faultcount - behind;
 566
 567                         /*
 568                          * Call the pager to retrieve the data, if any, after
 569                          * releasing the lock on the map.  We hold a ref on
 570                          * fs.object and the pages are PG_BUSY'd.
 571                          */
 572                         unlock_map(&fs);
 573
 574                         rv = faultcount ?
 575                             vm_pager_get_pages(fs.object, marray, faultcount,
 576                                 reqpage) : VM_PAGER_FAIL;
 577
 578                         if (rv == VM_PAGER_OK) {
 579                                 /*
 580                                  * Found the page. Leave it busy while we play
 581                                  * with it.
 582                                  */
 583
 584                                 /*
 585                                  * Relookup in case pager changed page. Pager
 586                                  * is responsible for disposition of old page
 587                                  * if moved.
 588                                  */
 589                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 590                                 if (!fs.m) {
 591                                         unlock_and_deallocate(&fs);
 592                                         goto RetryFault;
 593                                 }
 594
 595                                 hardfault++;
 596                                 break; /* break to PAGE HAS BEEN FOUND */
 597                         }
 598                         /*
 599                          * Remove the bogus page (which does not exist at this
 600                          * object/offset); before doing so, we must get back
 601                          * our object lock to preserve our invariant.
 602                          *
 603                          * Also wake up any other process that may want to bring
 604                          * in this page.
 605                          *
 606                          * If this is the top-level object, we must leave the
 607                          * busy page to prevent another process from rushing
 608                          * past us, and inserting the page in that object at
 609                          * the same time that we are.
 610                          */
 611                         if (rv == VM_PAGER_ERROR)
 612                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 613                                     curproc->p_pid, curproc->p_comm);
 614                         /*
 615                          * Data outside the range of the pager or an I/O error
 616                          */
 617                         /*
 618                          * XXX - the check for kernel_map is a kludge to work
 619                          * around having the machine panic on a kernel space
 620                          * fault w/ I/O error.
 621                          */
 622                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
 623                                 (rv == VM_PAGER_BAD)) {
 624                                 vm_page_lock_queues();
 625                                 vm_page_free(fs.m);
 626                                 vm_page_unlock_queues();
 627                                 fs.m = NULL;
 628                                 unlock_and_deallocate(&fs);
 629                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
 630                         }
 631                         if (fs.object != fs.first_object) {
 632                                 vm_page_lock_queues();
 633                                 vm_page_free(fs.m);
 634                                 vm_page_unlock_queues();
 635                                 fs.m = NULL;
 636                                 /*
 637                                  * XXX - we cannot just fall out at this
 638                                  * point, m has been freed and is invalid!
 639                                  */
 640                         }
 641                 }
 642
 643                 /*
 644                  * We get here if the object has default pager (or unwiring)
 645                  * or the pager doesn't have the page.
 646                  */
 647                 if (fs.object == fs.first_object)
 648                         fs.first_m = fs.m;
 649
 650                 /*
 651                  * Move on to the next object.  Lock the next object before
 652                  * unlocking the current one.
 653                  */
 654                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
 655                 next_object = fs.object->backing_object;
 656                 if (next_object == NULL) {
 657                         /*
 658                          * If there's no object left, fill the page in the top
 659                          * object with zeros.
 660                          */
 661                         if (fs.object != fs.first_object) {
 662                                 vm_object_pip_wakeup(fs.object);
 663                                 VM_OBJECT_UNLOCK(fs.object);
 664
 665                                 fs.object = fs.first_object;
 666                                 fs.pindex = fs.first_pindex;
 667                                 fs.m = fs.first_m;
 668                                 VM_OBJECT_LOCK(fs.object);
 669                         }
 670                         fs.first_m = NULL;
 671
 672                         /*
 673                          * Zero the page if necessary and mark it valid.
 674                          */
 675                         if ((fs.m->flags & PG_ZERO) == 0) {
 676                                 pmap_zero_page(fs.m);
 677                         } else {
 678                                 atomic_add_int(&cnt.v_ozfod, 1);
 679                         }
 680                         atomic_add_int(&cnt.v_zfod, 1);
 681                         fs.m->valid = VM_PAGE_BITS_ALL;
 682                         break;  /* break to PAGE HAS BEEN FOUND */
 683                 } else {
 684                         KASSERT(fs.object != next_object,
 685                             ("object loop %p", next_object));
 686                         VM_OBJECT_LOCK(next_object);
 687                         vm_object_pip_add(next_object, 1);
 688                         if (fs.object != fs.first_object)
 689                                 vm_object_pip_wakeup(fs.object);
 690                         VM_OBJECT_UNLOCK(fs.object);
 691                         fs.object = next_object;
 692                 }
 693         }
 694
 695         KASSERT((fs.m->flags & PG_BUSY) != 0,
 696             ("vm_fault: not busy after main loop"));
 697
 698         /*
 699          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
 700          * is held.]
 701          */
 702
 703         /*
 704          * If the page is being written, but isn't already owned by the
 705          * top-level object, we have to copy it into a new page owned by the
 706          * top-level object.
 707          */
 708         if (fs.object != fs.first_object) {
 709                 /*
 710                  * We only really need to copy if we want to write it.
 711                  */
 712                 if (fault_type & VM_PROT_WRITE) {
 713                         /*
 714                          * This allows pages to be virtually copied from a
 715                          * backing_object into the first_object, where the
 716                          * backing object has no other refs to it, and cannot
 717                          * gain any more refs.  Instead of a bcopy, we just
 718                          * move the page from the backing object to the
 719                          * first object.  Note that we must mark the page
 720                          * dirty in the first object so that it will go out
 721                          * to swap when needed.
 722                          */
 723                         is_first_object_locked = FALSE;
 724                         if (
 725                                 /*
 726                                  * Only one shadow object
 727                                  */
 728                                 (fs.object->shadow_count == 1) &&
 729                                 /*
 730                                  * No COW refs, except us
 731                                  */
 732                                 (fs.object->ref_count == 1) &&
 733                                 /*
 734                                  * No one else can look this object up
 735                                  */
 736                                 (fs.object->handle == NULL) &&
 737                                 /*
 738                                  * No other ways to look the object up
 739                                  */
 740                                 ((fs.object->type == OBJT_DEFAULT) ||
 741                                  (fs.object->type == OBJT_SWAP)) &&
 742                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
 743                                 /*
 744                                  * We don't chase down the shadow chain
 745                                  */
 746                             fs.object == fs.first_object->backing_object) {
 747                                 vm_page_lock_queues();
 748                                 /*
 749                                  * get rid of the unnecessary page
 750                                  */
 751                                 vm_page_free(fs.first_m);
 752                                 /*
 753                                  * grab the page and put it into the
 754                                  * process'es object.  The page is
 755                                  * automatically made dirty.
 756                                  */
 757                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
 758                                 vm_page_busy(fs.m);
 759                                 vm_page_unlock_queues();
 760                                 fs.first_m = fs.m;
 761                                 fs.m = NULL;
 762                                 atomic_add_int(&cnt.v_cow_optim, 1);
 763                         } else {
 764                                 /*
 765                                  * Oh, well, lets copy it.
 766                                  */
 767                                 pmap_copy_page(fs.m, fs.first_m);
 768                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
 769                         }
 770                         if (fs.m) {
 771                                 /*
 772                                  * We no longer need the old page or object.
 773                                  */
 774                                 release_page(&fs);
 775                         }
 776                         /*
 777                          * fs.object != fs.first_object due to above
 778                          * conditional
 779                          */
 780                         vm_object_pip_wakeup(fs.object);
 781                         VM_OBJECT_UNLOCK(fs.object);
 782                         /*
 783                          * Only use the new page below...
 784                          */
 785                         fs.object = fs.first_object;
 786                         fs.pindex = fs.first_pindex;
 787                         fs.m = fs.first_m;
 788                         if (!is_first_object_locked)
 789                                 VM_OBJECT_LOCK(fs.object);
 790                         atomic_add_int(&cnt.v_cow_faults, 1);
 791                 } else {
 792                         prot &= ~VM_PROT_WRITE;
 793                 }
 794         }
 795
 796         /*
 797          * We must verify that the maps have not changed since our last
 798          * lookup.
 799          */
 800         if (!fs.lookup_still_valid) {
 801                 vm_object_t retry_object;
 802                 vm_pindex_t retry_pindex;
 803                 vm_prot_t retry_prot;
 804
 805                 if (!vm_map_trylock_read(fs.map)) {
 806                         release_page(&fs);
 807                         unlock_and_deallocate(&fs);
 808                         goto RetryFault;
 809                 }
 810                 fs.lookup_still_valid = TRUE;
 811                 if (fs.map->timestamp != map_generation) {
 812                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
 813                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
 814
 815                         /*
 816                          * If we don't need the page any longer, put it on the inactive
 817                          * list (the easiest thing to do here).  If no one needs it,
 818                          * pageout will grab it eventually.
 819                          */
 820                         if (result != KERN_SUCCESS) {
 821                                 release_page(&fs);
 822                                 unlock_and_deallocate(&fs);
 823
 824                                 /*
 825                                  * If retry of map lookup would have blocked then
 826                                  * retry fault from start.
 827                                  */
 828                                 if (result == KERN_FAILURE)
 829                                         goto RetryFault;
 830                                 return (result);
 831                         }
 832                         if ((retry_object != fs.first_object) ||
 833                             (retry_pindex != fs.first_pindex)) {
 834                                 release_page(&fs);
 835                                 unlock_and_deallocate(&fs);
 836                                 goto RetryFault;
 837                         }
 838
 839                         /*
 840                          * Check whether the protection has changed or the object has
 841                          * been copied while we left the map unlocked. Changing from
 842                          * read to write permission is OK - we leave the page
 843                          * write-protected, and catch the write fault. Changing from
 844                          * write to read permission means that we can't mark the page
 845                          * write-enabled after all.
 846                          */
 847                         prot &= retry_prot;
 848                 }
 849         }
 850         if (prot & VM_PROT_WRITE) {
 851                 vm_page_lock_queues();
 852                 vm_page_flag_set(fs.m, PG_WRITEABLE);
 853                 vm_object_set_writeable_dirty(fs.m->object);
 854
 855                 /*
 856                  * If the fault is a write, we know that this page is being
 857                  * written NOW so dirty it explicitly to save on
 858                  * pmap_is_modified() calls later.
 859                  *
 860                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
 861                  * if the page is already dirty to prevent data written with
 862                  * the expectation of being synced from not being synced.
 863                  * Likewise if this entry does not request NOSYNC then make
 864                  * sure the page isn't marked NOSYNC.  Applications sharing
 865                  * data should use the same flags to avoid ping ponging.
 866                  *
 867                  * Also tell the backing pager, if any, that it should remove
 868                  * any swap backing since the page is now dirty.
 869                  */
 870                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
 871                         if (fs.m->dirty == 0)
 872                                 vm_page_flag_set(fs.m, PG_NOSYNC);
 873                 } else {
 874                         vm_page_flag_clear(fs.m, PG_NOSYNC);
 875                 }
 876                 vm_page_unlock_queues();
 877                 if (fault_flags & VM_FAULT_DIRTY) {
 878                         vm_page_dirty(fs.m);
 879                         vm_pager_page_unswapped(fs.m);
 880                 }
 881         }
 882
 883         /*
 884          * Page had better still be busy
 885          */
 886         KASSERT(fs.m->flags & PG_BUSY,
 887                 ("vm_fault: page %p not busy!", fs.m));
 888         /*
 889          * Sanity check: page must be completely valid or it is not fit to
 890          * map into user space.  vm_pager_get_pages() ensures this.
 891          */
 892         if (fs.m->valid != VM_PAGE_BITS_ALL) {
 893                 vm_page_zero_invalid(fs.m, TRUE);
 894                 printf("Warning: page %p partially invalid on fault\n", fs.m);
 895         }
 896         VM_OBJECT_UNLOCK(fs.object);
 897
 898         /*
 899          * Put this page into the physical map.  We had to do the unlock above
 900          * because pmap_enter() may sleep.  We don't put the page
 901          * back on the active queue until later so that the pageout daemon
 902          * won't find it (yet).
 903          */
 904         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
 905         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
 906                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
 907         }
 908         VM_OBJECT_LOCK(fs.object);
 909         vm_page_lock_queues();
 910         vm_page_flag_set(fs.m, PG_REFERENCED);
 911
 912         /*
 913          * If the page is not wired down, then put it where the pageout daemon
 914          * can find it.
 915          */
 916         if (fault_flags & VM_FAULT_WIRE_MASK) {
 917                 if (wired)
 918                         vm_page_wire(fs.m);
 919                 else
 920                         vm_page_unwire(fs.m, 1);
 921         } else {
 922                 vm_page_activate(fs.m);
 923         }
 924         vm_page_wakeup(fs.m);
 925         vm_page_unlock_queues();
 926
 927         /*
 928          * Unlock everything, and return
 929          */
 930         unlock_and_deallocate(&fs);
 931         PROC_LOCK(curproc);
 932         if ((curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
 933                 if (hardfault) {
 934                         curproc->p_stats->p_ru.ru_majflt++;
 935                 } else {
 936                         curproc->p_stats->p_ru.ru_minflt++;
 937                 }
 938         }
 939         PROC_UNLOCK(curproc);
 940
 941         return (KERN_SUCCESS);
 942 }
 943
 944 /*
 945  * vm_fault_prefault provides a quick way of clustering
 946  * pagefaults into a processes address space.  It is a "cousin"
 947  * of vm_map_pmap_enter, except it runs at page fault time instead
 948  * of mmap time.
 949  */
 950 static void
 951 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
 952 {
 953         int i;
 954         vm_offset_t addr, starta;
 955         vm_pindex_t pindex;
 956         vm_page_t m, mpte;
 957         vm_object_t object;
 958
 959         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
 960                 return;
 961
 962         object = entry->object.vm_object;
 963
 964         starta = addra - PFBAK * PAGE_SIZE;
 965         if (starta < entry->start) {
 966                 starta = entry->start;
 967         } else if (starta > addra) {
 968                 starta = 0;
 969         }
 970
 971         mpte = NULL;
 972         for (i = 0; i < PAGEORDER_SIZE; i++) {
 973                 vm_object_t backing_object, lobject;
 974
 975                 addr = addra + prefault_pageorder[i];
 976                 if (addr > addra + (PFFOR * PAGE_SIZE))
 977                         addr = 0;
 978
 979                 if (addr < starta || addr >= entry->end)
 980                         continue;
 981
 982                 if (!pmap_is_prefaultable(pmap, addr))
 983                         continue;
 984
 985                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
 986                 lobject = object;
 987                 VM_OBJECT_LOCK(lobject);
 988                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
 989                     lobject->type == OBJT_DEFAULT &&
 990                     (backing_object = lobject->backing_object) != NULL) {
 991                         if (lobject->backing_object_offset & PAGE_MASK)
 992                                 break;
 993                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
 994                         VM_OBJECT_LOCK(backing_object);
 995                         VM_OBJECT_UNLOCK(lobject);
 996                         lobject = backing_object;
 997                 }
 998                 /*
 999                  * give-up when a page is not in memory
1000                  */
1001                 if (m == NULL) {
1002                         VM_OBJECT_UNLOCK(lobject);
1003                         break;
1004                 }
1005                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
1006                         (m->busy == 0) &&
1007                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
1008
1009                         vm_page_lock_queues();
1010                         if (VM_PAGE_INQUEUE1(m, PQ_CACHE))
1011                                 vm_page_deactivate(m);
1012                         mpte = pmap_enter_quick(pmap, addr, m,
1013                             entry->protection, mpte);
1014                         vm_page_unlock_queues();
1015                 }
1016                 VM_OBJECT_UNLOCK(lobject);
1017         }
1018 }
1019
1020 /*
1021  *      vm_fault_quick:
1022  *
1023  *      Ensure that the requested virtual address, which may be in userland,
1024  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
1025  */
1026 int
1027 vm_fault_quick(caddr_t v, int prot)
1028 {
1029         int r;
1030
1031         if (prot & VM_PROT_WRITE)
1032                 r = subyte(v, fubyte(v));
1033         else
1034                 r = fubyte(v);
1035         return(r);
1036 }
1037
1038 /*
1039  *      vm_fault_wire:
1040  *
1041  *      Wire down a range of virtual addresses in a map.
1042  */
1043 int
1044 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1045     boolean_t user_wire, boolean_t fictitious)
1046 {
1047         vm_offset_t va;
1048         int rv;
1049
1050         /*
1051          * We simulate a fault to get the page and enter it in the physical
1052          * map.  For user wiring, we only ask for read access on currently
1053          * read-only sections.
1054          */
1055         for (va = start; va < end; va += PAGE_SIZE) {
1056                 rv = vm_fault(map, va,
1057                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
1058                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
1059                 if (rv) {
1060                         if (va != start)
1061                                 vm_fault_unwire(map, start, va, fictitious);
1062                         return (rv);
1063                 }
1064         }
1065         return (KERN_SUCCESS);
1066 }
1067
1068 /*
1069  *      vm_fault_unwire:
1070  *
1071  *      Unwire a range of virtual addresses in a map.
1072  */
1073 void
1074 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1075     boolean_t fictitious)
1076 {
1077         vm_paddr_t pa;
1078         vm_offset_t va;
1079         pmap_t pmap;
1080
1081         pmap = vm_map_pmap(map);
1082
1083         /*
1084          * Since the pages are wired down, we must be able to get their
1085          * mappings from the physical map system.
1086          */
1087         for (va = start; va < end; va += PAGE_SIZE) {
1088                 pa = pmap_extract(pmap, va);
1089                 if (pa != 0) {
1090                         pmap_change_wiring(pmap, va, FALSE);
1091                         if (!fictitious) {
1092                                 vm_page_lock_queues();
1093                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1094                                 vm_page_unlock_queues();
1095                         }
1096                 }
1097         }
1098 }
1099
1100 /*
1101  *      Routine:
1102  *              vm_fault_copy_entry
1103  *      Function:
1104  *              Copy all of the pages from a wired-down map entry to another.
1105  *
1106  *      In/out conditions:
1107  *              The source and destination maps must be locked for write.
1108  *              The source map entry must be wired down (or be a sharing map
1109  *              entry corresponding to a main map entry that is wired down).
1110  */
1111 void
1112 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
1113         vm_map_t dst_map;
1114         vm_map_t src_map;
1115         vm_map_entry_t dst_entry;
1116         vm_map_entry_t src_entry;
1117 {
1118         vm_object_t backing_object, dst_object, object;
1119         vm_object_t src_object;
1120         vm_ooffset_t dst_offset;
1121         vm_ooffset_t src_offset;
1122         vm_pindex_t pindex;
1123         vm_prot_t prot;
1124         vm_offset_t vaddr;
1125         vm_page_t dst_m;
1126         vm_page_t src_m;
1127
1128 #ifdef  lint
1129         src_map++;
1130 #endif  /* lint */
1131
1132         src_object = src_entry->object.vm_object;
1133         src_offset = src_entry->offset;
1134
1135         /*
1136          * Create the top-level object for the destination entry. (Doesn't
1137          * actually shadow anything - we copy the pages directly.)
1138          */
1139         dst_object = vm_object_allocate(OBJT_DEFAULT,
1140             OFF_TO_IDX(dst_entry->end - dst_entry->start));
1141
1142         VM_OBJECT_LOCK(dst_object);
1143         dst_entry->object.vm_object = dst_object;
1144         dst_entry->offset = 0;
1145
1146         prot = dst_entry->max_protection;
1147
1148         /*
1149          * Loop through all of the pages in the entry's range, copying each
1150          * one from the source object (it should be there) to the destination
1151          * object.
1152          */
1153         for (vaddr = dst_entry->start, dst_offset = 0;
1154             vaddr < dst_entry->end;
1155             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1156
1157                 /*
1158                  * Allocate a page in the destination object
1159                  */
1160                 do {
1161                         dst_m = vm_page_alloc(dst_object,
1162                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1163                         if (dst_m == NULL) {
1164                                 VM_OBJECT_UNLOCK(dst_object);
1165                                 VM_WAIT;
1166                                 VM_OBJECT_LOCK(dst_object);
1167                         }
1168                 } while (dst_m == NULL);
1169
1170                 /*
1171                  * Find the page in the source object, and copy it in.
1172                  * (Because the source is wired down, the page will be in
1173                  * memory.)
1174                  */
1175                 VM_OBJECT_LOCK(src_object);
1176                 object = src_object;
1177                 pindex = 0;
1178                 while ((src_m = vm_page_lookup(object, pindex +
1179                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
1180                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
1181                     (backing_object = object->backing_object) != NULL) {
1182                         /*
1183                          * Allow fallback to backing objects if we are reading.
1184                          */
1185                         VM_OBJECT_LOCK(backing_object);
1186                         pindex += OFF_TO_IDX(object->backing_object_offset);
1187                         VM_OBJECT_UNLOCK(object);
1188                         object = backing_object;
1189                 }
1190                 if (src_m == NULL)
1191                         panic("vm_fault_copy_wired: page missing");
1192                 pmap_copy_page(src_m, dst_m);
1193                 VM_OBJECT_UNLOCK(object);
1194                 dst_m->valid = VM_PAGE_BITS_ALL;
1195                 VM_OBJECT_UNLOCK(dst_object);
1196
1197                 /*
1198                  * Enter it in the pmap...
1199                  */
1200                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1201                 VM_OBJECT_LOCK(dst_object);
1202                 vm_page_lock_queues();
1203                 if ((prot & VM_PROT_WRITE) != 0)
1204                         vm_page_flag_set(dst_m, PG_WRITEABLE);
1205
1206                 /*
1207                  * Mark it no longer busy, and put it on the active list.
1208                  */
1209                 vm_page_activate(dst_m);
1210                 vm_page_wakeup(dst_m);
1211                 vm_page_unlock_queues();
1212         }
1213         VM_OBJECT_UNLOCK(dst_object);
1214 }
1215
1216
1217 /*
1218  * This routine checks around the requested page for other pages that
1219  * might be able to be faulted in.  This routine brackets the viable
1220  * pages for the pages to be paged in.
1221  *
1222  * Inputs:
1223  *      m, rbehind, rahead
1224  *
1225  * Outputs:
1226  *  marray (array of vm_page_t), reqpage (index of requested page)
1227  *
1228  * Return value:
1229  *  number of pages in marray
1230  *
1231  * This routine can't block.
1232  */
1233 static int
1234 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
1235         vm_page_t m;
1236         int rbehind;
1237         int rahead;
1238         vm_page_t *marray;
1239         int *reqpage;
1240 {
1241         int i,j;
1242         vm_object_t object;
1243         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1244         vm_page_t rtm;
1245         int cbehind, cahead;
1246
1247         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
1248
1249         object = m->object;
1250         pindex = m->pindex;
1251
1252         /*
1253          * we don't fault-ahead for device pager
1254          */
1255         if (object->type == OBJT_DEVICE) {
1256                 *reqpage = 0;
1257                 marray[0] = m;
1258                 return 1;
1259         }
1260
1261         /*
1262          * if the requested page is not available, then give up now
1263          */
1264         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1265                 return 0;
1266         }
1267
1268         if ((cbehind == 0) && (cahead == 0)) {
1269                 *reqpage = 0;
1270                 marray[0] = m;
1271                 return 1;
1272         }
1273
1274         if (rahead > cahead) {
1275                 rahead = cahead;
1276         }
1277
1278         if (rbehind > cbehind) {
1279                 rbehind = cbehind;
1280         }
1281
1282         /*
1283          * try to do any readahead that we might have free pages for.
1284          */
1285         if ((rahead + rbehind) >
1286                 ((cnt.v_free_count + cnt.v_cache_count) - cnt.v_free_reserved)) {
1287                 pagedaemon_wakeup();
1288                 marray[0] = m;
1289                 *reqpage = 0;
1290                 return 1;
1291         }
1292
1293         /*
1294          * scan backward for the read behind pages -- in memory
1295          */
1296         if (pindex > 0) {
1297                 if (rbehind > pindex) {
1298                         rbehind = pindex;
1299                         startpindex = 0;
1300                 } else {
1301                         startpindex = pindex - rbehind;
1302                 }
1303
1304                 if ((rtm = TAILQ_PREV(m, pglist, listq)) != NULL &&
1305                     rtm->pindex >= startpindex)
1306                         startpindex = rtm->pindex + 1;
1307
1308                 for (i = 0, tpindex = startpindex; tpindex < pindex; i++, tpindex++) {
1309
1310                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1311                         if (rtm == NULL) {
1312                                 vm_page_lock_queues();
1313                                 for (j = 0; j < i; j++) {
1314                                         vm_page_free(marray[j]);
1315                                 }
1316                                 vm_page_unlock_queues();
1317                                 marray[0] = m;
1318                                 *reqpage = 0;
1319                                 return 1;
1320                         }
1321
1322                         marray[i] = rtm;
1323                 }
1324         } else {
1325                 startpindex = 0;
1326                 i = 0;
1327         }
1328
1329         marray[i] = m;
1330         /* page offset of the required page */
1331         *reqpage = i;
1332
1333         tpindex = pindex + 1;
1334         i++;
1335
1336         /*
1337          * scan forward for the read ahead pages
1338          */
1339         endpindex = tpindex + rahead;
1340         if ((rtm = TAILQ_NEXT(m, listq)) != NULL && rtm->pindex < endpindex)
1341                 endpindex = rtm->pindex;
1342         if (endpindex > object->size)
1343                 endpindex = object->size;
1344
1345         for (; tpindex < endpindex; i++, tpindex++) {
1346
1347                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1348                 if (rtm == NULL) {
1349                         break;
1350                 }
1351
1352                 marray[i] = rtm;
1353         }
1354
1355         /* return number of bytes of pages */
1356         return i;
1357 }