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