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