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