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->first_object->flags & OBJ_NEEDGIANT)
 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.first_object->flags & OBJ_NEEDGIANT)
 294                 mtx_lock(&Giant);
 295         VM_OBJECT_LOCK(fs.first_object);
 296         vm_object_reference_locked(fs.first_object);
 297         fs.vp = vnode_pager_lock(fs.first_object);
 298         KASSERT(fs.vp == NULL || !fs.map->system_map,
 299             ("vm_fault: vnode-backed object mapped by system map"));
 300         KASSERT((fs.first_object->flags & OBJ_NEEDGIANT) == 0 ||
 301             !fs.map->system_map,
 302             ("vm_fault: Object requiring giant mapped by system map"));
 303         if (fs.first_object->flags & OBJ_NEEDGIANT && debug_mpsafevm)
 304                 mtx_unlock(&Giant);
 305         vm_object_pip_add(fs.first_object, 1);
 306
 307         fs.lookup_still_valid = TRUE;
 308
 309         if (wired)
 310                 fault_type = prot;
 311
 312         fs.first_m = NULL;
 313
 314         /*
 315          * Search for the page at object/offset.
 316          */
 317         fs.object = fs.first_object;
 318         fs.pindex = fs.first_pindex;
 319         while (TRUE) {
 320                 /*
 321                  * If the object is dead, we stop here
 322                  */
 323                 if (fs.object->flags & OBJ_DEAD) {
 324                         unlock_and_deallocate(&fs);
 325                         return (KERN_PROTECTION_FAILURE);
 326                 }
 327
 328                 /*
 329                  * See if page is resident
 330                  */
 331                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 332                 if (fs.m != NULL) {
 333                         int queue;
 334
 335                         /*
 336                          * check for page-based copy on write.
 337                          * We check fs.object == fs.first_object so
 338                          * as to ensure the legacy COW mechanism is
 339                          * used when the page in question is part of
 340                          * a shadow object.  Otherwise, vm_page_cowfault()
 341                          * removes the page from the backing object,
 342                          * which is not what we want.
 343                          */
 344                         vm_page_lock_queues();
 345                         if ((fs.m->cow) &&
 346                             (fault_type & VM_PROT_WRITE) &&
 347                             (fs.object == fs.first_object)) {
 348                                 vm_page_cowfault(fs.m);
 349                                 vm_page_unlock_queues();
 350                                 unlock_and_deallocate(&fs);
 351                                 goto RetryFault;
 352                         }
 353
 354                         /*
 355                          * Wait/Retry if the page is busy.  We have to do this
 356                          * if the page is busy via either PG_BUSY or
 357                          * vm_page_t->busy because the vm_pager may be using
 358                          * vm_page_t->busy for pageouts ( and even pageins if
 359                          * it is the vnode pager ), and we could end up trying
 360                          * to pagein and pageout the same page simultaneously.
 361                          *
 362                          * We can theoretically allow the busy case on a read
 363                          * fault if the page is marked valid, but since such
 364                          * pages are typically already pmap'd, putting that
 365                          * special case in might be more effort then it is
 366                          * worth.  We cannot under any circumstances mess
 367                          * around with a vm_page_t->busy page except, perhaps,
 368                          * to pmap it.
 369                          */
 370                         if ((fs.m->flags & PG_BUSY) || fs.m->busy) {
 371                                 vm_page_unlock_queues();
 372                                 VM_OBJECT_UNLOCK(fs.object);
 373                                 if (fs.object != fs.first_object) {
 374                                         VM_OBJECT_LOCK(fs.first_object);
 375                                         vm_page_lock_queues();
 376                                         vm_page_free(fs.first_m);
 377                                         vm_page_unlock_queues();
 378                                         vm_object_pip_wakeup(fs.first_object);
 379                                         VM_OBJECT_UNLOCK(fs.first_object);
 380                                         fs.first_m = NULL;
 381                                 }
 382                                 unlock_map(&fs);
 383                                 if (fs.vp != NULL) {
 384                                         int vfslck;
 385
 386                                         vfslck = VFS_LOCK_GIANT(fs.vp->v_mount);
 387                                         vput(fs.vp);
 388                                         fs.vp = NULL;
 389                                         VFS_UNLOCK_GIANT(vfslck);
 390                                 }
 391                                 VM_OBJECT_LOCK(fs.object);
 392                                 if (fs.m == vm_page_lookup(fs.object,
 393                                     fs.pindex)) {
 394                                         vm_page_lock_queues();
 395                                         if (!vm_page_sleep_if_busy(fs.m, TRUE,
 396                                             "vmpfw"))
 397                                                 vm_page_unlock_queues();
 398                                 }
 399                                 vm_object_pip_wakeup(fs.object);
 400                                 VM_OBJECT_UNLOCK(fs.object);
 401                                 atomic_add_int(&cnt.v_intrans, 1);
 402                                 if (fs.first_object->flags & OBJ_NEEDGIANT)
 403                                         VM_UNLOCK_GIANT();
 404                                 vm_object_deallocate(fs.first_object);
 405                                 goto RetryFault;
 406                         }
 407                         queue = fs.m->queue;
 408
 409                         vm_pageq_remove_nowakeup(fs.m);
 410
 411                         if ((queue - fs.m->pc) == PQ_CACHE && vm_page_count_severe()) {
 412                                 vm_page_activate(fs.m);
 413                                 vm_page_unlock_queues();
 414                                 unlock_and_deallocate(&fs);
 415                                 VM_WAITPFAULT;
 416                                 goto RetryFault;
 417                         }
 418
 419                         /*
 420                          * Mark page busy for other processes, and the
 421                          * pagedaemon.  If it still isn't completely valid
 422                          * (readable), jump to readrest, else break-out ( we
 423                          * found the page ).
 424                          */
 425                         vm_page_busy(fs.m);
 426                         vm_page_unlock_queues();
 427                         if (((fs.m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) &&
 428                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
 429                                 goto readrest;
 430                         }
 431
 432                         break;
 433                 }
 434
 435                 /*
 436                  * Page is not resident, If this is the search termination
 437                  * or the pager might contain the page, allocate a new page.
 438                  */
 439                 if (TRYPAGER || fs.object == fs.first_object) {
 440                         if (fs.pindex >= fs.object->size) {
 441                                 unlock_and_deallocate(&fs);
 442                                 return (KERN_PROTECTION_FAILURE);
 443                         }
 444
 445                         /*
 446                          * Allocate a new page for this object/offset pair.
 447                          */
 448                         fs.m = NULL;
 449                         if (!vm_page_count_severe()) {
 450                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 451                                     (fs.vp || fs.object->backing_object)? VM_ALLOC_NORMAL: VM_ALLOC_ZERO);
 452                         }
 453                         if (fs.m == NULL) {
 454                                 unlock_and_deallocate(&fs);
 455                                 VM_WAITPFAULT;
 456                                 goto RetryFault;
 457                         }
 458                 }
 459
 460 readrest:
 461                 /*
 462                  * We have found a valid page or we have allocated a new page.
 463                  * The page thus may not be valid or may not be entirely
 464                  * valid.
 465                  *
 466                  * Attempt to fault-in the page if there is a chance that the
 467                  * pager has it, and potentially fault in additional pages
 468                  * at the same time.
 469                  */
 470                 if (TRYPAGER) {
 471                         int rv;
 472                         int reqpage;
 473                         int ahead, behind;
 474                         u_char behavior = vm_map_entry_behavior(fs.entry);
 475
 476                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 477                                 ahead = 0;
 478                                 behind = 0;
 479                         } else {
 480                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
 481                                 if (behind > VM_FAULT_READ_BEHIND)
 482                                         behind = VM_FAULT_READ_BEHIND;
 483
 484                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
 485                                 if (ahead > VM_FAULT_READ_AHEAD)
 486                                         ahead = VM_FAULT_READ_AHEAD;
 487                         }
 488                         is_first_object_locked = FALSE;
 489                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
 490                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
 491                               fs.pindex >= fs.entry->lastr &&
 492                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
 493                             (fs.first_object == fs.object ||
 494                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
 495                             fs.first_object->type != OBJT_DEVICE) {
 496                                 vm_pindex_t firstpindex, tmppindex;
 497
 498                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
 499                                         firstpindex = 0;
 500                                 else
 501                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
 502
 503                                 vm_page_lock_queues();
 504                                 /*
 505                                  * note: partially valid pages cannot be
 506                                  * included in the lookahead - NFS piecemeal
 507                                  * writes will barf on it badly.
 508                                  */
 509                                 for (tmppindex = fs.first_pindex - 1;
 510                                         tmppindex >= firstpindex;
 511                                         --tmppindex) {
 512                                         vm_page_t mt;
 513
 514                                         mt = vm_page_lookup(fs.first_object, tmppindex);
 515                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
 516                                                 break;
 517                                         if (mt->busy ||
 518                                                 (mt->flags & (PG_BUSY | PG_FICTITIOUS | PG_UNMANAGED)) ||
 519                                                 mt->hold_count ||
 520                                                 mt->wire_count)
 521                                                 continue;
 522                                         pmap_remove_all(mt);
 523                                         if (mt->dirty) {
 524                                                 vm_page_deactivate(mt);
 525                                         } else {
 526                                                 vm_page_cache(mt);
 527                                         }
 528                                 }
 529                                 vm_page_unlock_queues();
 530                                 ahead += behind;
 531                                 behind = 0;
 532                         }
 533                         if (is_first_object_locked)
 534                                 VM_OBJECT_UNLOCK(fs.first_object);
 535                         /*
 536                          * now we find out if any other pages should be paged
 537                          * in at this time this routine checks to see if the
 538                          * pages surrounding this fault reside in the same
 539                          * object as the page for this fault.  If they do,
 540                          * then they are faulted in also into the object.  The
 541                          * array "marray" returned contains an array of
 542                          * vm_page_t structs where one of them is the
 543                          * vm_page_t passed to the routine.  The reqpage
 544                          * return value is the index into the marray for the
 545                          * vm_page_t passed to the routine.
 546                          *
 547                          * fs.m plus the additional pages are PG_BUSY'd.
 548                          *
 549                          * XXX vm_fault_additional_pages() can block
 550                          * without releasing the map lock.
 551                          */
 552                         faultcount = vm_fault_additional_pages(
 553                             fs.m, behind, ahead, marray, &reqpage);
 554
 555                         /*
 556                          * update lastr imperfectly (we do not know how much
 557                          * getpages will actually read), but good enough.
 558                          *
 559                          * XXX The following assignment modifies the map
 560                          * without holding a write lock on it.
 561                          */
 562                         fs.entry->lastr = fs.pindex + faultcount - behind;
 563
 564                         /*
 565                          * Call the pager to retrieve the data, if any, after
 566                          * releasing the lock on the map.  We hold a ref on
 567                          * fs.object and the pages are PG_BUSY'd.
 568                          */
 569                         unlock_map(&fs);
 570
 571                         rv = faultcount ?
 572                             vm_pager_get_pages(fs.object, marray, faultcount,
 573                                 reqpage) : VM_PAGER_FAIL;
 574
 575                         if (rv == VM_PAGER_OK) {
 576                                 /*
 577                                  * Found the page. Leave it busy while we play
 578                                  * with it.
 579                                  */
 580
 581                                 /*
 582                                  * Relookup in case pager changed page. Pager
 583                                  * is responsible for disposition of old page
 584                                  * if moved.
 585                                  */
 586                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 587                                 if (!fs.m) {
 588                                         unlock_and_deallocate(&fs);
 589                                         goto RetryFault;
 590                                 }
 591
 592                                 hardfault++;
 593                                 break; /* break to PAGE HAS BEEN FOUND */
 594                         }
 595                         /*
 596                          * Remove the bogus page (which does not exist at this
 597                          * object/offset); before doing so, we must get back
 598                          * our object lock to preserve our invariant.
 599                          *
 600                          * Also wake up any other process that may want to bring
 601                          * in this page.
 602                          *
 603                          * If this is the top-level object, we must leave the
 604                          * busy page to prevent another process from rushing
 605                          * past us, and inserting the page in that object at
 606                          * the same time that we are.
 607                          */
 608                         if (rv == VM_PAGER_ERROR)
 609                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 610                                     curproc->p_pid, curproc->p_comm);
 611                         /*
 612                          * Data outside the range of the pager or an I/O error
 613                          */
 614                         /*
 615                          * XXX - the check for kernel_map is a kludge to work
 616                          * around having the machine panic on a kernel space
 617                          * fault w/ I/O error.
 618                          */
 619                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
 620                                 (rv == VM_PAGER_BAD)) {
 621                                 vm_page_lock_queues();
 622                                 vm_page_free(fs.m);
 623                                 vm_page_unlock_queues();
 624                                 fs.m = NULL;
 625                                 unlock_and_deallocate(&fs);
 626                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
 627                         }
 628                         if (fs.object != fs.first_object) {
 629                                 vm_page_lock_queues();
 630                                 vm_page_free(fs.m);
 631                                 vm_page_unlock_queues();
 632                                 fs.m = NULL;
 633                                 /*
 634                                  * XXX - we cannot just fall out at this
 635                                  * point, m has been freed and is invalid!
 636                                  */
 637                         }
 638                 }
 639
 640                 /*
 641                  * We get here if the object has default pager (or unwiring)
 642                  * or the pager doesn't have the page.
 643                  */
 644                 if (fs.object == fs.first_object)
 645                         fs.first_m = fs.m;
 646
 647                 /*
 648                  * Move on to the next object.  Lock the next object before
 649                  * unlocking the current one.
 650                  */
 651                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
 652                 next_object = fs.object->backing_object;
 653                 if (next_object == NULL) {
 654                         /*
 655                          * If there's no object left, fill the page in the top
 656                          * object with zeros.
 657                          */
 658                         if (fs.object != fs.first_object) {
 659                                 vm_object_pip_wakeup(fs.object);
 660                                 VM_OBJECT_UNLOCK(fs.object);
 661
 662                                 fs.object = fs.first_object;
 663                                 fs.pindex = fs.first_pindex;
 664                                 fs.m = fs.first_m;
 665                                 VM_OBJECT_LOCK(fs.object);
 666                         }
 667                         fs.first_m = NULL;
 668
 669                         /*
 670                          * Zero the page if necessary and mark it valid.
 671                          */
 672                         if ((fs.m->flags & PG_ZERO) == 0) {
 673                                 pmap_zero_page(fs.m);
 674                         } else {
 675                                 atomic_add_int(&cnt.v_ozfod, 1);
 676                         }
 677                         atomic_add_int(&cnt.v_zfod, 1);
 678                         fs.m->valid = VM_PAGE_BITS_ALL;
 679                         break;  /* break to PAGE HAS BEEN FOUND */
 680                 } else {
 681                         KASSERT(fs.object != next_object,
 682                             ("object loop %p", next_object));
 683                         VM_OBJECT_LOCK(next_object);
 684                         vm_object_pip_add(next_object, 1);
 685                         if (fs.object != fs.first_object)
 686                                 vm_object_pip_wakeup(fs.object);
 687                         VM_OBJECT_UNLOCK(fs.object);
 688                         fs.object = next_object;
 689                 }
 690         }
 691
 692         KASSERT((fs.m->flags & PG_BUSY) != 0,
 693             ("vm_fault: not busy after main loop"));
 694
 695         /*
 696          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
 697          * is held.]
 698          */
 699
 700         /*
 701          * If the page is being written, but isn't already owned by the
 702          * top-level object, we have to copy it into a new page owned by the
 703          * top-level object.
 704          */
 705         if (fs.object != fs.first_object) {
 706                 /*
 707                  * We only really need to copy if we want to write it.
 708                  */
 709                 if (fault_type & VM_PROT_WRITE) {
 710                         /*
 711                          * This allows pages to be virtually copied from a
 712                          * backing_object into the first_object, where the
 713                          * backing object has no other refs to it, and cannot
 714                          * gain any more refs.  Instead of a bcopy, we just
 715                          * move the page from the backing object to the
 716                          * first object.  Note that we must mark the page
 717                          * dirty in the first object so that it will go out
 718                          * to swap when needed.
 719                          */
 720                         is_first_object_locked = FALSE;
 721                         if (
 722                                 /*
 723                                  * Only one shadow object
 724                                  */
 725                                 (fs.object->shadow_count == 1) &&
 726                                 /*
 727                                  * No COW refs, except us
 728                                  */
 729                                 (fs.object->ref_count == 1) &&
 730                                 /*
 731                                  * No one else can look this object up
 732                                  */
 733                                 (fs.object->handle == NULL) &&
 734                                 /*
 735                                  * No other ways to look the object up
 736                                  */
 737                                 ((fs.object->type == OBJT_DEFAULT) ||
 738                                  (fs.object->type == OBJT_SWAP)) &&
 739                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
 740                                 /*
 741                                  * We don't chase down the shadow chain
 742                                  */
 743                             fs.object == fs.first_object->backing_object) {
 744                                 vm_page_lock_queues();
 745                                 /*
 746                                  * get rid of the unnecessary page
 747                                  */
 748                                 pmap_remove_all(fs.first_m);
 749                                 vm_page_free(fs.first_m);
 750                                 /*
 751                                  * grab the page and put it into the
 752                                  * process'es object.  The page is
 753                                  * automatically made dirty.
 754                                  */
 755                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
 756                                 vm_page_busy(fs.m);
 757                                 vm_page_unlock_queues();
 758                                 fs.first_m = fs.m;
 759                                 fs.m = NULL;
 760                                 atomic_add_int(&cnt.v_cow_optim, 1);
 761                         } else {
 762                                 /*
 763                                  * Oh, well, lets copy it.
 764                                  */
 765                                 pmap_copy_page(fs.m, fs.first_m);
 766                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
 767                         }
 768                         if (fs.m) {
 769                                 /*
 770                                  * We no longer need the old page or object.
 771                                  */
 772                                 release_page(&fs);
 773                         }
 774                         /*
 775                          * fs.object != fs.first_object due to above
 776                          * conditional
 777                          */
 778                         vm_object_pip_wakeup(fs.object);
 779                         VM_OBJECT_UNLOCK(fs.object);
 780                         /*
 781                          * Only use the new page below...
 782                          */
 783                         fs.object = fs.first_object;
 784                         fs.pindex = fs.first_pindex;
 785                         fs.m = fs.first_m;
 786                         if (!is_first_object_locked)
 787                                 VM_OBJECT_LOCK(fs.object);
 788                         atomic_add_int(&cnt.v_cow_faults, 1);
 789                 } else {
 790                         prot &= ~VM_PROT_WRITE;
 791                 }
 792         }
 793
 794         /*
 795          * We must verify that the maps have not changed since our last
 796          * lookup.
 797          */
 798         if (!fs.lookup_still_valid) {
 799                 vm_object_t retry_object;
 800                 vm_pindex_t retry_pindex;
 801                 vm_prot_t retry_prot;
 802
 803                 if (!vm_map_trylock_read(fs.map)) {
 804                         release_page(&fs);
 805                         unlock_and_deallocate(&fs);
 806                         goto RetryFault;
 807                 }
 808                 fs.lookup_still_valid = TRUE;
 809                 if (fs.map->timestamp != map_generation) {
 810                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
 811                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
 812
 813                         /*
 814                          * If we don't need the page any longer, put it on the active
 815                          * list (the easiest thing to do here).  If no one needs it,
 816                          * pageout will grab it eventually.
 817                          */
 818                         if (result != KERN_SUCCESS) {
 819                                 release_page(&fs);
 820                                 unlock_and_deallocate(&fs);
 821
 822                                 /*
 823                                  * If retry of map lookup would have blocked then
 824                                  * retry fault from start.
 825                                  */
 826                                 if (result == KERN_FAILURE)
 827                                         goto RetryFault;
 828                                 return (result);
 829                         }
 830                         if ((retry_object != fs.first_object) ||
 831                             (retry_pindex != fs.first_pindex)) {
 832                                 release_page(&fs);
 833                                 unlock_and_deallocate(&fs);
 834                                 goto RetryFault;
 835                         }
 836
 837                         /*
 838                          * Check whether the protection has changed or the object has
 839                          * been copied while we left the map unlocked. Changing from
 840                          * read to write permission is OK - we leave the page
 841                          * write-protected, and catch the write fault. Changing from
 842                          * write to read permission means that we can't mark the page
 843                          * write-enabled after all.
 844                          */
 845                         prot &= retry_prot;
 846                 }
 847         }
 848         if (prot & VM_PROT_WRITE) {
 849                 vm_page_lock_queues();
 850                 vm_page_flag_set(fs.m, PG_WRITEABLE);
 851                 vm_object_set_writeable_dirty(fs.m->object);
 852
 853                 /*
 854                  * If the fault is a write, we know that this page is being
 855                  * written NOW so dirty it explicitly to save on
 856                  * pmap_is_modified() calls later.
 857                  *
 858                  * If this is a NOSYNC mmap we do not want to set PG_NOSYNC
 859                  * if the page is already dirty to prevent data written with
 860                  * the expectation of being synced from not being synced.
 861                  * Likewise if this entry does not request NOSYNC then make
 862                  * sure the page isn't marked NOSYNC.  Applications sharing
 863                  * data should use the same flags to avoid ping ponging.
 864                  *
 865                  * Also tell the backing pager, if any, that it should remove
 866                  * any swap backing since the page is now dirty.
 867                  */
 868                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
 869                         if (fs.m->dirty == 0)
 870                                 vm_page_flag_set(fs.m, PG_NOSYNC);
 871                 } else {
 872                         vm_page_flag_clear(fs.m, PG_NOSYNC);
 873                 }
 874                 vm_page_unlock_queues();
 875                 if (fault_flags & VM_FAULT_DIRTY) {
 876                         vm_page_dirty(fs.m);
 877                         vm_pager_page_unswapped(fs.m);
 878                 }
 879         }
 880
 881         /*
 882          * Page had better still be busy
 883          */
 884         KASSERT(fs.m->flags & PG_BUSY,
 885                 ("vm_fault: page %p not busy!", fs.m));
 886         /*
 887          * Sanity check: page must be completely valid or it is not fit to
 888          * map into user space.  vm_pager_get_pages() ensures this.
 889          */
 890         if (fs.m->valid != VM_PAGE_BITS_ALL) {
 891                 vm_page_zero_invalid(fs.m, TRUE);
 892                 printf("Warning: page %p partially invalid on fault\n", fs.m);
 893         }
 894         VM_OBJECT_UNLOCK(fs.object);
 895
 896         /*
 897          * Put this page into the physical map.  We had to do the unlock above
 898          * because pmap_enter() may sleep.  We don't put the page
 899          * back on the active queue until later so that the pageout daemon
 900          * won't find it (yet).
 901          */
 902         pmap_enter(fs.map->pmap, vaddr, fs.m, prot, wired);
 903         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
 904                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
 905         }
 906         VM_OBJECT_LOCK(fs.object);
 907         vm_page_lock_queues();
 908         vm_page_flag_set(fs.m, PG_REFERENCED);
 909
 910         /*
 911          * If the page is not wired down, then put it where the pageout daemon
 912          * can find it.
 913          */
 914         if (fault_flags & VM_FAULT_WIRE_MASK) {
 915                 if (wired)
 916                         vm_page_wire(fs.m);
 917                 else
 918                         vm_page_unwire(fs.m, 1);
 919         } else {
 920                 vm_page_activate(fs.m);
 921         }
 922         vm_page_wakeup(fs.m);
 923         vm_page_unlock_queues();
 924
 925         /*
 926          * Unlock everything, and return
 927          */
 928         unlock_and_deallocate(&fs);
 929         PROC_LOCK(curproc);
 930         if ((curproc->p_sflag & PS_INMEM) && curproc->p_stats) {
 931                 if (hardfault) {
 932                         curproc->p_stats->p_ru.ru_majflt++;
 933                 } else {
 934                         curproc->p_stats->p_ru.ru_minflt++;
 935                 }
 936         }
 937         PROC_UNLOCK(curproc);
 938
 939         return (KERN_SUCCESS);
 940 }
 941
 942 /*
 943  * vm_fault_prefault provides a quick way of clustering
 944  * pagefaults into a processes address space.  It is a "cousin"
 945  * of vm_map_pmap_enter, except it runs at page fault time instead
 946  * of mmap time.
 947  */
 948 static void
 949 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
 950 {
 951         int i;
 952         vm_offset_t addr, starta;
 953         vm_pindex_t pindex;
 954         vm_page_t m, mpte;
 955         vm_object_t object;
 956
 957         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
 958                 return;
 959
 960         object = entry->object.vm_object;
 961
 962         starta = addra - PFBAK * PAGE_SIZE;
 963         if (starta < entry->start) {
 964                 starta = entry->start;
 965         } else if (starta > addra) {
 966                 starta = 0;
 967         }
 968
 969         mpte = NULL;
 970         for (i = 0; i < PAGEORDER_SIZE; i++) {
 971                 vm_object_t backing_object, lobject;
 972
 973                 addr = addra + prefault_pageorder[i];
 974                 if (addr > addra + (PFFOR * PAGE_SIZE))
 975                         addr = 0;
 976
 977                 if (addr < starta || addr >= entry->end)
 978                         continue;
 979
 980                 if (!pmap_is_prefaultable(pmap, addr))
 981                         continue;
 982
 983                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
 984                 lobject = object;
 985                 VM_OBJECT_LOCK(lobject);
 986                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
 987                     lobject->type == OBJT_DEFAULT &&
 988                     (backing_object = lobject->backing_object) != NULL) {
 989                         if (lobject->backing_object_offset & PAGE_MASK)
 990                                 break;
 991                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
 992                         VM_OBJECT_LOCK(backing_object);
 993                         VM_OBJECT_UNLOCK(lobject);
 994                         lobject = backing_object;
 995                 }
 996                 /*
 997                  * give-up when a page is not in memory
 998                  */
 999                 if (m == NULL) {
1000                         VM_OBJECT_UNLOCK(lobject);
1001                         break;
1002                 }
1003                 if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
1004                         (m->busy == 0) &&
1005                     (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
1006
1007                         vm_page_lock_queues();
1008                         if ((m->queue - m->pc) == PQ_CACHE)
1009                                 vm_page_deactivate(m);
1010                         mpte = pmap_enter_quick(pmap, addr, m,
1011                             entry->protection, mpte);
1012                         vm_page_unlock_queues();
1013                 }
1014                 VM_OBJECT_UNLOCK(lobject);
1015         }
1016 }
1017
1018 /*
1019  *      vm_fault_quick:
1020  *
1021  *      Ensure that the requested virtual address, which may be in userland,
1022  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
1023  */
1024 int
1025 vm_fault_quick(caddr_t v, int prot)
1026 {
1027         int r;
1028
1029         if (prot & VM_PROT_WRITE)
1030                 r = subyte(v, fubyte(v));
1031         else
1032                 r = fubyte(v);
1033         return(r);
1034 }
1035
1036 /*
1037  *      vm_fault_wire:
1038  *
1039  *      Wire down a range of virtual addresses in a map.
1040  */
1041 int
1042 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1043     boolean_t user_wire, boolean_t fictitious)
1044 {
1045         vm_offset_t va;
1046         int rv;
1047
1048         /*
1049          * We simulate a fault to get the page and enter it in the physical
1050          * map.  For user wiring, we only ask for read access on currently
1051          * read-only sections.
1052          */
1053         for (va = start; va < end; va += PAGE_SIZE) {
1054                 rv = vm_fault(map, va,
1055                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
1056                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
1057                 if (rv) {
1058                         if (va != start)
1059                                 vm_fault_unwire(map, start, va, fictitious);
1060                         return (rv);
1061                 }
1062         }
1063         return (KERN_SUCCESS);
1064 }
1065
1066 /*
1067  *      vm_fault_unwire:
1068  *
1069  *      Unwire a range of virtual addresses in a map.
1070  */
1071 void
1072 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1073     boolean_t fictitious)
1074 {
1075         vm_paddr_t pa;
1076         vm_offset_t va;
1077         pmap_t pmap;
1078
1079         pmap = vm_map_pmap(map);
1080
1081         /*
1082          * Since the pages are wired down, we must be able to get their
1083          * mappings from the physical map system.
1084          */
1085         for (va = start; va < end; va += PAGE_SIZE) {
1086                 pa = pmap_extract(pmap, va);
1087                 if (pa != 0) {
1088                         pmap_change_wiring(pmap, va, FALSE);
1089                         if (!fictitious) {
1090                                 vm_page_lock_queues();
1091                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1092                                 vm_page_unlock_queues();
1093                         }
1094                 }
1095         }
1096 }
1097
1098 /*
1099  *      Routine:
1100  *              vm_fault_copy_entry
1101  *      Function:
1102  *              Copy all of the pages from a wired-down map entry to another.
1103  *
1104  *      In/out conditions:
1105  *              The source and destination maps must be locked for write.
1106  *              The source map entry must be wired down (or be a sharing map
1107  *              entry corresponding to a main map entry that is wired down).
1108  */
1109 void
1110 vm_fault_copy_entry(dst_map, src_map, dst_entry, src_entry)
1111         vm_map_t dst_map;
1112         vm_map_t src_map;
1113         vm_map_entry_t dst_entry;
1114         vm_map_entry_t src_entry;
1115 {
1116         vm_object_t backing_object, dst_object, object;
1117         vm_object_t src_object;
1118         vm_ooffset_t dst_offset;
1119         vm_ooffset_t src_offset;
1120         vm_pindex_t pindex;
1121         vm_prot_t prot;
1122         vm_offset_t vaddr;
1123         vm_page_t dst_m;
1124         vm_page_t src_m;
1125
1126 #ifdef  lint
1127         src_map++;
1128 #endif  /* lint */
1129
1130         src_object = src_entry->object.vm_object;
1131         src_offset = src_entry->offset;
1132
1133         /*
1134          * Create the top-level object for the destination entry. (Doesn't
1135          * actually shadow anything - we copy the pages directly.)
1136          */
1137         dst_object = vm_object_allocate(OBJT_DEFAULT,
1138             OFF_TO_IDX(dst_entry->end - dst_entry->start));
1139
1140         VM_OBJECT_LOCK(dst_object);
1141         dst_entry->object.vm_object = dst_object;
1142         dst_entry->offset = 0;
1143
1144         prot = dst_entry->max_protection;
1145
1146         /*
1147          * Loop through all of the pages in the entry's range, copying each
1148          * one from the source object (it should be there) to the destination
1149          * object.
1150          */
1151         for (vaddr = dst_entry->start, dst_offset = 0;
1152             vaddr < dst_entry->end;
1153             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1154
1155                 /*
1156                  * Allocate a page in the destination object
1157                  */
1158                 do {
1159                         dst_m = vm_page_alloc(dst_object,
1160                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1161                         if (dst_m == NULL) {
1162                                 VM_OBJECT_UNLOCK(dst_object);
1163                                 VM_WAIT;
1164                                 VM_OBJECT_LOCK(dst_object);
1165                         }
1166                 } while (dst_m == NULL);
1167
1168                 /*
1169                  * Find the page in the source object, and copy it in.
1170                  * (Because the source is wired down, the page will be in
1171                  * memory.)
1172                  */
1173                 VM_OBJECT_LOCK(src_object);
1174                 object = src_object;
1175                 pindex = 0;
1176                 while ((src_m = vm_page_lookup(object, pindex +
1177                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
1178                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
1179                     (backing_object = object->backing_object) != NULL) {
1180                         /*
1181                          * Allow fallback to backing objects if we are reading.
1182                          */
1183                         VM_OBJECT_LOCK(backing_object);
1184                         pindex += OFF_TO_IDX(object->backing_object_offset);
1185                         VM_OBJECT_UNLOCK(object);
1186                         object = backing_object;
1187                 }
1188                 if (src_m == NULL)
1189                         panic("vm_fault_copy_wired: page missing");
1190                 pmap_copy_page(src_m, dst_m);
1191                 VM_OBJECT_UNLOCK(object);
1192                 dst_m->valid = VM_PAGE_BITS_ALL;
1193                 VM_OBJECT_UNLOCK(dst_object);
1194
1195                 /*
1196                  * Enter it in the pmap...
1197                  */
1198                 pmap_enter(dst_map->pmap, vaddr, dst_m, prot, FALSE);
1199                 VM_OBJECT_LOCK(dst_object);
1200                 vm_page_lock_queues();
1201                 if ((prot & VM_PROT_WRITE) != 0)
1202                         vm_page_flag_set(dst_m, PG_WRITEABLE);
1203
1204                 /*
1205                  * Mark it no longer busy, and put it on the active list.
1206                  */
1207                 vm_page_activate(dst_m);
1208                 vm_page_wakeup(dst_m);
1209                 vm_page_unlock_queues();
1210         }
1211         VM_OBJECT_UNLOCK(dst_object);
1212 }
1213
1214
1215 /*
1216  * This routine checks around the requested page for other pages that
1217  * might be able to be faulted in.  This routine brackets the viable
1218  * pages for the pages to be paged in.
1219  *
1220  * Inputs:
1221  *      m, rbehind, rahead
1222  *
1223  * Outputs:
1224  *  marray (array of vm_page_t), reqpage (index of requested page)
1225  *
1226  * Return value:
1227  *  number of pages in marray
1228  *
1229  * This routine can't block.
1230  */
1231 static int
1232 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
1233         vm_page_t m;
1234         int rbehind;
1235         int rahead;
1236         vm_page_t *marray;
1237         int *reqpage;
1238 {
1239         int i,j;
1240         vm_object_t object;
1241         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1242         vm_page_t rtm;
1243         int cbehind, cahead;
1244
1245         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
1246
1247         object = m->object;
1248         pindex = m->pindex;
1249
1250         /*
1251          * we don't fault-ahead for device pager
1252          */
1253         if (object->type == OBJT_DEVICE) {
1254                 *reqpage = 0;
1255                 marray[0] = m;
1256                 return 1;
1257         }
1258
1259         /*
1260          * if the requested page is not available, then give up now
1261          */
1262         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1263                 return 0;
1264         }
1265
1266         if ((cbehind == 0) && (cahead == 0)) {
1267                 *reqpage = 0;
1268                 marray[0] = m;
1269                 return 1;
1270         }
1271
1272         if (rahead > cahead) {
1273                 rahead = cahead;
1274         }
1275
1276         if (rbehind > cbehind) {
1277                 rbehind = cbehind;
1278         }
1279
1280         /*
1281          * try to do any readahead that we might have free pages for.
1282          */
1283         if ((rahead + rbehind) >
1284                 ((cnt.v_free_count + cnt.v_cache_count) - cnt.v_free_reserved)) {
1285                 pagedaemon_wakeup();
1286                 marray[0] = m;
1287                 *reqpage = 0;
1288                 return 1;
1289         }
1290
1291         /*
1292          * scan backward for the read behind pages -- in memory
1293          */
1294         if (pindex > 0) {
1295                 if (rbehind > pindex) {
1296                         rbehind = pindex;
1297                         startpindex = 0;
1298                 } else {
1299                         startpindex = pindex - rbehind;
1300                 }
1301
1302                 for (tpindex = pindex - 1; tpindex >= startpindex; tpindex -= 1) {
1303                         if (vm_page_lookup(object, tpindex)) {
1304                                 startpindex = tpindex + 1;
1305                                 break;
1306                         }
1307                         if (tpindex == 0)
1308                                 break;
1309                 }
1310
1311                 for (i = 0, tpindex = startpindex; tpindex < pindex; i++, tpindex++) {
1312
1313                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1314                         if (rtm == NULL) {
1315                                 vm_page_lock_queues();
1316                                 for (j = 0; j < i; j++) {
1317                                         vm_page_free(marray[j]);
1318                                 }
1319                                 vm_page_unlock_queues();
1320                                 marray[0] = m;
1321                                 *reqpage = 0;
1322                                 return 1;
1323                         }
1324
1325                         marray[i] = rtm;
1326                 }
1327         } else {
1328                 startpindex = 0;
1329                 i = 0;
1330         }
1331
1332         marray[i] = m;
1333         /* page offset of the required page */
1334         *reqpage = i;
1335
1336         tpindex = pindex + 1;
1337         i++;
1338
1339         /*
1340          * scan forward for the read ahead pages
1341          */
1342         endpindex = tpindex + rahead;
1343         if (endpindex > object->size)
1344                 endpindex = object->size;
1345
1346         for (; tpindex < endpindex; i++, tpindex++) {
1347
1348                 if (vm_page_lookup(object, tpindex)) {
1349                         break;
1350                 }
1351
1352                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL);
1353                 if (rtm == NULL) {
1354                         break;
1355                 }
1356
1357                 marray[i] = rtm;
1358         }
1359
1360         /* return number of bytes of pages */
1361         return i;
1362 }