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 "opt_vm.h"
  78
  79 #include <sys/param.h>
  80 #include <sys/systm.h>
  81 #include <sys/kernel.h>
  82 #include <sys/lock.h>
  83 #include <sys/mutex.h>
  84 #include <sys/proc.h>
  85 #include <sys/resourcevar.h>
  86 #include <sys/sysctl.h>
  87 #include <sys/vmmeter.h>
  88 #include <sys/vnode.h>
  89
  90 #include <vm/vm.h>
  91 #include <vm/vm_param.h>
  92 #include <vm/pmap.h>
  93 #include <vm/vm_map.h>
  94 #include <vm/vm_object.h>
  95 #include <vm/vm_page.h>
  96 #include <vm/vm_pageout.h>
  97 #include <vm/vm_kern.h>
  98 #include <vm/vm_pager.h>
  99 #include <vm/vnode_pager.h>
 100 #include <vm/vm_extern.h>
 101
 102 #include <sys/mount.h>  /* XXX Temporary for VFS_LOCK_GIANT() */
 103
 104 #define PFBAK 4
 105 #define PFFOR 4
 106 #define PAGEORDER_SIZE (PFBAK+PFFOR)
 107
 108 static int prefault_pageorder[] = {
 109         -1 * PAGE_SIZE, 1 * PAGE_SIZE,
 110         -2 * PAGE_SIZE, 2 * PAGE_SIZE,
 111         -3 * PAGE_SIZE, 3 * PAGE_SIZE,
 112         -4 * PAGE_SIZE, 4 * PAGE_SIZE
 113 };
 114
 115 static int vm_fault_additional_pages(vm_page_t, int, int, vm_page_t *, int *);
 116 static void vm_fault_prefault(pmap_t, vm_offset_t, vm_map_entry_t);
 117
 118 #define VM_FAULT_READ_AHEAD 8
 119 #define VM_FAULT_READ_BEHIND 7
 120 #define VM_FAULT_READ (VM_FAULT_READ_AHEAD+VM_FAULT_READ_BEHIND+1)
 121
 122 struct faultstate {
 123         vm_page_t m;
 124         vm_object_t object;
 125         vm_pindex_t pindex;
 126         vm_page_t first_m;
 127         vm_object_t     first_object;
 128         vm_pindex_t first_pindex;
 129         vm_map_t map;
 130         vm_map_entry_t entry;
 131         int lookup_still_valid;
 132         struct vnode *vp;
 133         int vfslocked;
 134 };
 135
 136 static inline void
 137 release_page(struct faultstate *fs)
 138 {
 139
 140         vm_page_wakeup(fs->m);
 141         vm_page_lock_queues();
 142         vm_page_deactivate(fs->m);
 143         vm_page_unlock_queues();
 144         fs->m = NULL;
 145 }
 146
 147 static inline void
 148 unlock_map(struct faultstate *fs)
 149 {
 150
 151         if (fs->lookup_still_valid) {
 152                 vm_map_lookup_done(fs->map, fs->entry);
 153                 fs->lookup_still_valid = FALSE;
 154         }
 155 }
 156
 157 static void
 158 unlock_and_deallocate(struct faultstate *fs)
 159 {
 160
 161         vm_object_pip_wakeup(fs->object);
 162         VM_OBJECT_UNLOCK(fs->object);
 163         if (fs->object != fs->first_object) {
 164                 VM_OBJECT_LOCK(fs->first_object);
 165                 vm_page_lock_queues();
 166                 vm_page_free(fs->first_m);
 167                 vm_page_unlock_queues();
 168                 vm_object_pip_wakeup(fs->first_object);
 169                 VM_OBJECT_UNLOCK(fs->first_object);
 170                 fs->first_m = NULL;
 171         }
 172         vm_object_deallocate(fs->first_object);
 173         unlock_map(fs);
 174         if (fs->vp != NULL) {
 175                 vput(fs->vp);
 176                 fs->vp = NULL;
 177         }
 178         VFS_UNLOCK_GIANT(fs->vfslocked);
 179         fs->vfslocked = 0;
 180 }
 181
 182 /*
 183  * TRYPAGER - used by vm_fault to calculate whether the pager for the
 184  *            current object *might* contain the page.
 185  *
 186  *            default objects are zero-fill, there is no real pager.
 187  */
 188 #define TRYPAGER        (fs.object->type != OBJT_DEFAULT && \
 189                         (((fault_flags & VM_FAULT_WIRE_MASK) == 0) || wired))
 190
 191 /*
 192  *      vm_fault:
 193  *
 194  *      Handle a page fault occurring at the given address,
 195  *      requiring the given permissions, in the map specified.
 196  *      If successful, the page is inserted into the
 197  *      associated physical map.
 198  *
 199  *      NOTE: the given address should be truncated to the
 200  *      proper page address.
 201  *
 202  *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 203  *      a standard error specifying why the fault is fatal is returned.
 204  *
 205  *
 206  *      The map in question must be referenced, and remains so.
 207  *      Caller may hold no locks.
 208  */
 209 int
 210 vm_fault(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 211          int fault_flags)
 212 {
 213         vm_prot_t prot;
 214         int is_first_object_locked, result;
 215         boolean_t are_queues_locked, growstack, wired;
 216         int map_generation;
 217         vm_object_t next_object;
 218         vm_page_t marray[VM_FAULT_READ];
 219         int hardfault;
 220         int faultcount, ahead, behind;
 221         struct faultstate fs;
 222         struct vnode *vp;
 223         int locked, error;
 224
 225         hardfault = 0;
 226         growstack = TRUE;
 227         PCPU_INC(cnt.v_vm_faults);
 228         fs.vp = NULL;
 229         fs.vfslocked = 0;
 230         faultcount = behind = 0;
 231
 232 RetryFault:;
 233
 234         /*
 235          * Find the backing store object and offset into it to begin the
 236          * search.
 237          */
 238         fs.map = map;
 239         result = vm_map_lookup(&fs.map, vaddr, fault_type, &fs.entry,
 240             &fs.first_object, &fs.first_pindex, &prot, &wired);
 241         if (result != KERN_SUCCESS) {
 242                 if (result != KERN_PROTECTION_FAILURE ||
 243                     (fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE) {
 244                         if (growstack && result == KERN_INVALID_ADDRESS &&
 245                             map != kernel_map && curproc != NULL) {
 246                                 result = vm_map_growstack(curproc, vaddr);
 247                                 if (result != KERN_SUCCESS)
 248                                         return (KERN_FAILURE);
 249                                 growstack = FALSE;
 250                                 goto RetryFault;
 251                         }
 252                         return (result);
 253                 }
 254
 255                 /*
 256                  * If we are user-wiring a r/w segment, and it is COW, then
 257                  * we need to do the COW operation.  Note that we don't COW
 258                  * currently RO sections now, because it is NOT desirable
 259                  * to COW .text.  We simply keep .text from ever being COW'ed
 260                  * and take the heat that one cannot debug wired .text sections.
 261                  */
 262                 result = vm_map_lookup(&fs.map, vaddr,
 263                         VM_PROT_READ|VM_PROT_WRITE|VM_PROT_OVERRIDE_WRITE,
 264                         &fs.entry, &fs.first_object, &fs.first_pindex, &prot, &wired);
 265                 if (result != KERN_SUCCESS)
 266                         return (result);
 267
 268                 /*
 269                  * If we don't COW now, on a user wire, the user will never
 270                  * be able to write to the mapping.  If we don't make this
 271                  * restriction, the bookkeeping would be nearly impossible.
 272                  *
 273                  * XXX The following assignment modifies the map without
 274                  * holding a write lock on it.
 275                  */
 276                 if ((fs.entry->protection & VM_PROT_WRITE) == 0)
 277                         fs.entry->max_protection &= ~VM_PROT_WRITE;
 278         }
 279
 280         map_generation = fs.map->timestamp;
 281
 282         if (fs.entry->eflags & MAP_ENTRY_NOFAULT) {
 283                 panic("vm_fault: fault on nofault entry, addr: %lx",
 284                     (u_long)vaddr);
 285         }
 286
 287         /*
 288          * Make a reference to this object to prevent its disposal while we
 289          * are messing with it.  Once we have the reference, the map is free
 290          * to be diddled.  Since objects reference their shadows (and copies),
 291          * they will stay around as well.
 292          *
 293          * Bump the paging-in-progress count to prevent size changes (e.g.
 294          * truncation operations) during I/O.  This must be done after
 295          * obtaining the vnode lock in order to avoid possible deadlocks.
 296          */
 297         VM_OBJECT_LOCK(fs.first_object);
 298         vm_object_reference_locked(fs.first_object);
 299         vm_object_pip_add(fs.first_object, 1);
 300
 301         fs.lookup_still_valid = TRUE;
 302
 303         if (wired)
 304                 fault_type = prot;
 305
 306         fs.first_m = NULL;
 307
 308         /*
 309          * Search for the page at object/offset.
 310          */
 311         fs.object = fs.first_object;
 312         fs.pindex = fs.first_pindex;
 313         while (TRUE) {
 314                 /*
 315                  * If the object is dead, we stop here
 316                  */
 317                 if (fs.object->flags & OBJ_DEAD) {
 318                         unlock_and_deallocate(&fs);
 319                         return (KERN_PROTECTION_FAILURE);
 320                 }
 321
 322                 /*
 323                  * See if page is resident
 324                  */
 325                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 326                 if (fs.m != NULL) {
 327                         /*
 328                          * check for page-based copy on write.
 329                          * We check fs.object == fs.first_object so
 330                          * as to ensure the legacy COW mechanism is
 331                          * used when the page in question is part of
 332                          * a shadow object.  Otherwise, vm_page_cowfault()
 333                          * removes the page from the backing object,
 334                          * which is not what we want.
 335                          */
 336                         vm_page_lock_queues();
 337                         if ((fs.m->cow) &&
 338                             (fault_type & VM_PROT_WRITE) &&
 339                             (fs.object == fs.first_object)) {
 340                                 vm_page_cowfault(fs.m);
 341                                 vm_page_unlock_queues();
 342                                 unlock_and_deallocate(&fs);
 343                                 goto RetryFault;
 344                         }
 345
 346                         /*
 347                          * Wait/Retry if the page is busy.  We have to do this
 348                          * if the page is busy via either VPO_BUSY or
 349                          * vm_page_t->busy because the vm_pager may be using
 350                          * vm_page_t->busy for pageouts ( and even pageins if
 351                          * it is the vnode pager ), and we could end up trying
 352                          * to pagein and pageout the same page simultaneously.
 353                          *
 354                          * We can theoretically allow the busy case on a read
 355                          * fault if the page is marked valid, but since such
 356                          * pages are typically already pmap'd, putting that
 357                          * special case in might be more effort then it is
 358                          * worth.  We cannot under any circumstances mess
 359                          * around with a vm_page_t->busy page except, perhaps,
 360                          * to pmap it.
 361                          */
 362                         if ((fs.m->oflags & VPO_BUSY) || fs.m->busy) {
 363                                 vm_page_unlock_queues();
 364                                 VM_OBJECT_UNLOCK(fs.object);
 365                                 if (fs.object != fs.first_object) {
 366                                         VM_OBJECT_LOCK(fs.first_object);
 367                                         vm_page_lock_queues();
 368                                         vm_page_free(fs.first_m);
 369                                         vm_page_unlock_queues();
 370                                         vm_object_pip_wakeup(fs.first_object);
 371                                         VM_OBJECT_UNLOCK(fs.first_object);
 372                                         fs.first_m = NULL;
 373                                 }
 374                                 unlock_map(&fs);
 375                                 VM_OBJECT_LOCK(fs.object);
 376                                 if (fs.m == vm_page_lookup(fs.object,
 377                                     fs.pindex)) {
 378                                         vm_page_sleep_if_busy(fs.m, TRUE,
 379                                             "vmpfw");
 380                                 }
 381                                 vm_object_pip_wakeup(fs.object);
 382                                 VM_OBJECT_UNLOCK(fs.object);
 383                                 PCPU_INC(cnt.v_intrans);
 384                                 vm_object_deallocate(fs.first_object);
 385                                 goto RetryFault;
 386                         }
 387                         vm_pageq_remove(fs.m);
 388                         vm_page_unlock_queues();
 389
 390                         /*
 391                          * Mark page busy for other processes, and the
 392                          * pagedaemon.  If it still isn't completely valid
 393                          * (readable), jump to readrest, else break-out ( we
 394                          * found the page ).
 395                          */
 396                         vm_page_busy(fs.m);
 397                         if (fs.m->valid != VM_PAGE_BITS_ALL &&
 398                                 fs.m->object != kernel_object && fs.m->object != kmem_object) {
 399                                 goto readrest;
 400                         }
 401
 402                         break;
 403                 }
 404
 405                 /*
 406                  * Page is not resident, If this is the search termination
 407                  * or the pager might contain the page, allocate a new page.
 408                  */
 409                 if (TRYPAGER || fs.object == fs.first_object) {
 410                         if (fs.pindex >= fs.object->size) {
 411                                 unlock_and_deallocate(&fs);
 412                                 return (KERN_PROTECTION_FAILURE);
 413                         }
 414
 415                         /*
 416                          * Allocate a new page for this object/offset pair.
 417                          */
 418                         fs.m = NULL;
 419                         if (!vm_page_count_severe()) {
 420 #if VM_NRESERVLEVEL > 0
 421                                 if ((fs.object->flags & OBJ_COLORED) == 0) {
 422                                         fs.object->flags |= OBJ_COLORED;
 423                                         fs.object->pg_color = atop(vaddr) -
 424                                             fs.pindex;
 425                                 }
 426 #endif
 427                                 fs.m = vm_page_alloc(fs.object, fs.pindex,
 428                                     (fs.object->type == OBJT_VNODE ||
 429                                      fs.object->backing_object != NULL) ?
 430                                     VM_ALLOC_NORMAL : VM_ALLOC_ZERO);
 431                         }
 432                         if (fs.m == NULL) {
 433                                 unlock_and_deallocate(&fs);
 434                                 VM_WAITPFAULT;
 435                                 goto RetryFault;
 436                         } else if (fs.m->valid == VM_PAGE_BITS_ALL)
 437                                 break;
 438                 }
 439
 440 readrest:
 441                 /*
 442                  * We have found a valid page or we have allocated a new page.
 443                  * The page thus may not be valid or may not be entirely
 444                  * valid.
 445                  *
 446                  * Attempt to fault-in the page if there is a chance that the
 447                  * pager has it, and potentially fault in additional pages
 448                  * at the same time.
 449                  */
 450                 if (TRYPAGER) {
 451                         int rv;
 452                         int reqpage = 0;
 453                         u_char behavior = vm_map_entry_behavior(fs.entry);
 454
 455                         if (behavior == MAP_ENTRY_BEHAV_RANDOM) {
 456                                 ahead = 0;
 457                                 behind = 0;
 458                         } else {
 459                                 behind = (vaddr - fs.entry->start) >> PAGE_SHIFT;
 460                                 if (behind > VM_FAULT_READ_BEHIND)
 461                                         behind = VM_FAULT_READ_BEHIND;
 462
 463                                 ahead = ((fs.entry->end - vaddr) >> PAGE_SHIFT) - 1;
 464                                 if (ahead > VM_FAULT_READ_AHEAD)
 465                                         ahead = VM_FAULT_READ_AHEAD;
 466                         }
 467                         is_first_object_locked = FALSE;
 468                         if ((behavior == MAP_ENTRY_BEHAV_SEQUENTIAL ||
 469                              (behavior != MAP_ENTRY_BEHAV_RANDOM &&
 470                               fs.pindex >= fs.entry->lastr &&
 471                               fs.pindex < fs.entry->lastr + VM_FAULT_READ)) &&
 472                             (fs.first_object == fs.object ||
 473                              (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object))) &&
 474                             fs.first_object->type != OBJT_DEVICE &&
 475                             fs.first_object->type != OBJT_PHYS &&
 476                             fs.first_object->type != OBJT_SG) {
 477                                 vm_pindex_t firstpindex, tmppindex;
 478
 479                                 if (fs.first_pindex < 2 * VM_FAULT_READ)
 480                                         firstpindex = 0;
 481                                 else
 482                                         firstpindex = fs.first_pindex - 2 * VM_FAULT_READ;
 483
 484                                 are_queues_locked = FALSE;
 485                                 /*
 486                                  * note: partially valid pages cannot be
 487                                  * included in the lookahead - NFS piecemeal
 488                                  * writes will barf on it badly.
 489                                  */
 490                                 for (tmppindex = fs.first_pindex - 1;
 491                                         tmppindex >= firstpindex;
 492                                         --tmppindex) {
 493                                         vm_page_t mt;
 494
 495                                         mt = vm_page_lookup(fs.first_object, tmppindex);
 496                                         if (mt == NULL || (mt->valid != VM_PAGE_BITS_ALL))
 497                                                 break;
 498                                         if (mt->busy ||
 499                                             (mt->oflags & VPO_BUSY))
 500                                                 continue;
 501                                         if (!are_queues_locked) {
 502                                                 are_queues_locked = TRUE;
 503                                                 vm_page_lock_queues();
 504                                         }
 505                                         if (mt->hold_count ||
 506                                                 mt->wire_count)
 507                                                 continue;
 508                                         pmap_remove_all(mt);
 509                                         if (mt->dirty) {
 510                                                 vm_page_deactivate(mt);
 511                                         } else {
 512                                                 vm_page_cache(mt);
 513                                         }
 514                                 }
 515                                 if (are_queues_locked)
 516                                         vm_page_unlock_queues();
 517                                 ahead += behind;
 518                                 behind = 0;
 519                         }
 520                         if (is_first_object_locked)
 521                                 VM_OBJECT_UNLOCK(fs.first_object);
 522
 523                         /*
 524                          * Call the pager to retrieve the data, if any, after
 525                          * releasing the lock on the map.  We hold a ref on
 526                          * fs.object and the pages are VPO_BUSY'd.
 527                          */
 528                         unlock_map(&fs);
 529
 530 vnode_lock:
 531                         if (fs.object->type == OBJT_VNODE) {
 532                                 vp = fs.object->handle;
 533                                 if (vp == fs.vp)
 534                                         goto vnode_locked;
 535                                 else if (fs.vp != NULL) {
 536                                         vput(fs.vp);
 537                                         fs.vp = NULL;
 538                                 }
 539                                 locked = VOP_ISLOCKED(vp);
 540
 541                                 if (VFS_NEEDSGIANT(vp->v_mount) && !fs.vfslocked) {
 542                                         fs.vfslocked = 1;
 543                                         if (!mtx_trylock(&Giant)) {
 544                                                 VM_OBJECT_UNLOCK(fs.object);
 545                                                 mtx_lock(&Giant);
 546                                                 VM_OBJECT_LOCK(fs.object);
 547                                                 goto vnode_lock;
 548                                         }
 549                                 }
 550                                 if (locked != LK_EXCLUSIVE)
 551                                         locked = LK_SHARED;
 552                                 /* Do not sleep for vnode lock while fs.m is busy */
 553                                 error = vget(vp, locked | LK_CANRECURSE |
 554                                     LK_NOWAIT, curthread);
 555                                 if (error != 0) {
 556                                         int vfslocked;
 557
 558                                         vfslocked = fs.vfslocked;
 559                                         fs.vfslocked = 0; /* Keep Giant */
 560                                         vhold(vp);
 561                                         release_page(&fs);
 562                                         unlock_and_deallocate(&fs);
 563                                         error = vget(vp, locked | LK_RETRY |
 564                                             LK_CANRECURSE, curthread);
 565                                         vdrop(vp);
 566                                         fs.vp = vp;
 567                                         fs.vfslocked = vfslocked;
 568                                         KASSERT(error == 0,
 569                                             ("vm_fault: vget failed"));
 570                                         goto RetryFault;
 571                                 }
 572                                 fs.vp = vp;
 573                         }
 574 vnode_locked:
 575                         KASSERT(fs.vp == NULL || !fs.map->system_map,
 576                             ("vm_fault: vnode-backed object mapped by system map"));
 577
 578                         /*
 579                          * now we find out if any other pages should be paged
 580                          * in at this time this routine checks to see if the
 581                          * pages surrounding this fault reside in the same
 582                          * object as the page for this fault.  If they do,
 583                          * then they are faulted in also into the object.  The
 584                          * array "marray" returned contains an array of
 585                          * vm_page_t structs where one of them is the
 586                          * vm_page_t passed to the routine.  The reqpage
 587                          * return value is the index into the marray for the
 588                          * vm_page_t passed to the routine.
 589                          *
 590                          * fs.m plus the additional pages are VPO_BUSY'd.
 591                          */
 592                         faultcount = vm_fault_additional_pages(
 593                             fs.m, behind, ahead, marray, &reqpage);
 594
 595                         rv = faultcount ?
 596                             vm_pager_get_pages(fs.object, marray, faultcount,
 597                                 reqpage) : VM_PAGER_FAIL;
 598
 599                         if (rv == VM_PAGER_OK) {
 600                                 /*
 601                                  * Found the page. Leave it busy while we play
 602                                  * with it.
 603                                  */
 604
 605                                 /*
 606                                  * Relookup in case pager changed page. Pager
 607                                  * is responsible for disposition of old page
 608                                  * if moved.
 609                                  */
 610                                 fs.m = vm_page_lookup(fs.object, fs.pindex);
 611                                 if (!fs.m) {
 612                                         unlock_and_deallocate(&fs);
 613                                         goto RetryFault;
 614                                 }
 615
 616                                 hardfault++;
 617                                 break; /* break to PAGE HAS BEEN FOUND */
 618                         }
 619                         /*
 620                          * Remove the bogus page (which does not exist at this
 621                          * object/offset); before doing so, we must get back
 622                          * our object lock to preserve our invariant.
 623                          *
 624                          * Also wake up any other process that may want to bring
 625                          * in this page.
 626                          *
 627                          * If this is the top-level object, we must leave the
 628                          * busy page to prevent another process from rushing
 629                          * past us, and inserting the page in that object at
 630                          * the same time that we are.
 631                          */
 632                         if (rv == VM_PAGER_ERROR)
 633                                 printf("vm_fault: pager read error, pid %d (%s)\n",
 634                                     curproc->p_pid, curproc->p_comm);
 635                         /*
 636                          * Data outside the range of the pager or an I/O error
 637                          */
 638                         /*
 639                          * XXX - the check for kernel_map is a kludge to work
 640                          * around having the machine panic on a kernel space
 641                          * fault w/ I/O error.
 642                          */
 643                         if (((fs.map != kernel_map) && (rv == VM_PAGER_ERROR)) ||
 644                                 (rv == VM_PAGER_BAD)) {
 645                                 vm_page_lock_queues();
 646                                 vm_page_free(fs.m);
 647                                 vm_page_unlock_queues();
 648                                 fs.m = NULL;
 649                                 unlock_and_deallocate(&fs);
 650                                 return ((rv == VM_PAGER_ERROR) ? KERN_FAILURE : KERN_PROTECTION_FAILURE);
 651                         }
 652                         if (fs.object != fs.first_object) {
 653                                 vm_page_lock_queues();
 654                                 vm_page_free(fs.m);
 655                                 vm_page_unlock_queues();
 656                                 fs.m = NULL;
 657                                 /*
 658                                  * XXX - we cannot just fall out at this
 659                                  * point, m has been freed and is invalid!
 660                                  */
 661                         }
 662                 }
 663
 664                 /*
 665                  * We get here if the object has default pager (or unwiring)
 666                  * or the pager doesn't have the page.
 667                  */
 668                 if (fs.object == fs.first_object)
 669                         fs.first_m = fs.m;
 670
 671                 /*
 672                  * Move on to the next object.  Lock the next object before
 673                  * unlocking the current one.
 674                  */
 675                 fs.pindex += OFF_TO_IDX(fs.object->backing_object_offset);
 676                 next_object = fs.object->backing_object;
 677                 if (next_object == NULL) {
 678                         /*
 679                          * If there's no object left, fill the page in the top
 680                          * object with zeros.
 681                          */
 682                         if (fs.object != fs.first_object) {
 683                                 vm_object_pip_wakeup(fs.object);
 684                                 VM_OBJECT_UNLOCK(fs.object);
 685
 686                                 fs.object = fs.first_object;
 687                                 fs.pindex = fs.first_pindex;
 688                                 fs.m = fs.first_m;
 689                                 VM_OBJECT_LOCK(fs.object);
 690                         }
 691                         fs.first_m = NULL;
 692
 693                         /*
 694                          * Zero the page if necessary and mark it valid.
 695                          */
 696                         if ((fs.m->flags & PG_ZERO) == 0) {
 697                                 pmap_zero_page(fs.m);
 698                         } else {
 699                                 PCPU_INC(cnt.v_ozfod);
 700                         }
 701                         PCPU_INC(cnt.v_zfod);
 702                         fs.m->valid = VM_PAGE_BITS_ALL;
 703                         break;  /* break to PAGE HAS BEEN FOUND */
 704                 } else {
 705                         KASSERT(fs.object != next_object,
 706                             ("object loop %p", next_object));
 707                         VM_OBJECT_LOCK(next_object);
 708                         vm_object_pip_add(next_object, 1);
 709                         if (fs.object != fs.first_object)
 710                                 vm_object_pip_wakeup(fs.object);
 711                         VM_OBJECT_UNLOCK(fs.object);
 712                         fs.object = next_object;
 713                 }
 714         }
 715
 716         KASSERT((fs.m->oflags & VPO_BUSY) != 0,
 717             ("vm_fault: not busy after main loop"));
 718
 719         /*
 720          * PAGE HAS BEEN FOUND. [Loop invariant still holds -- the object lock
 721          * is held.]
 722          */
 723
 724         /*
 725          * If the page is being written, but isn't already owned by the
 726          * top-level object, we have to copy it into a new page owned by the
 727          * top-level object.
 728          */
 729         if (fs.object != fs.first_object) {
 730                 /*
 731                  * We only really need to copy if we want to write it.
 732                  */
 733                 if (fault_type & VM_PROT_WRITE) {
 734                         /*
 735                          * This allows pages to be virtually copied from a
 736                          * backing_object into the first_object, where the
 737                          * backing object has no other refs to it, and cannot
 738                          * gain any more refs.  Instead of a bcopy, we just
 739                          * move the page from the backing object to the
 740                          * first object.  Note that we must mark the page
 741                          * dirty in the first object so that it will go out
 742                          * to swap when needed.
 743                          */
 744                         is_first_object_locked = FALSE;
 745                         if (
 746                                 /*
 747                                  * Only one shadow object
 748                                  */
 749                                 (fs.object->shadow_count == 1) &&
 750                                 /*
 751                                  * No COW refs, except us
 752                                  */
 753                                 (fs.object->ref_count == 1) &&
 754                                 /*
 755                                  * No one else can look this object up
 756                                  */
 757                                 (fs.object->handle == NULL) &&
 758                                 /*
 759                                  * No other ways to look the object up
 760                                  */
 761                                 ((fs.object->type == OBJT_DEFAULT) ||
 762                                  (fs.object->type == OBJT_SWAP)) &&
 763                             (is_first_object_locked = VM_OBJECT_TRYLOCK(fs.first_object)) &&
 764                                 /*
 765                                  * We don't chase down the shadow chain
 766                                  */
 767                             fs.object == fs.first_object->backing_object) {
 768                                 vm_page_lock_queues();
 769                                 /*
 770                                  * get rid of the unnecessary page
 771                                  */
 772                                 vm_page_free(fs.first_m);
 773                                 /*
 774                                  * grab the page and put it into the
 775                                  * process'es object.  The page is
 776                                  * automatically made dirty.
 777                                  */
 778                                 vm_page_rename(fs.m, fs.first_object, fs.first_pindex);
 779                                 vm_page_unlock_queues();
 780                                 vm_page_busy(fs.m);
 781                                 fs.first_m = fs.m;
 782                                 fs.m = NULL;
 783                                 PCPU_INC(cnt.v_cow_optim);
 784                         } else {
 785                                 /*
 786                                  * Oh, well, lets copy it.
 787                                  */
 788                                 pmap_copy_page(fs.m, fs.first_m);
 789                                 fs.first_m->valid = VM_PAGE_BITS_ALL;
 790                         }
 791                         if (fs.m) {
 792                                 /*
 793                                  * We no longer need the old page or object.
 794                                  */
 795                                 release_page(&fs);
 796                         }
 797                         /*
 798                          * fs.object != fs.first_object due to above
 799                          * conditional
 800                          */
 801                         vm_object_pip_wakeup(fs.object);
 802                         VM_OBJECT_UNLOCK(fs.object);
 803                         /*
 804                          * Only use the new page below...
 805                          */
 806                         fs.object = fs.first_object;
 807                         fs.pindex = fs.first_pindex;
 808                         fs.m = fs.first_m;
 809                         if (!is_first_object_locked)
 810                                 VM_OBJECT_LOCK(fs.object);
 811                         PCPU_INC(cnt.v_cow_faults);
 812                 } else {
 813                         prot &= ~VM_PROT_WRITE;
 814                 }
 815         }
 816
 817         /*
 818          * We must verify that the maps have not changed since our last
 819          * lookup.
 820          */
 821         if (!fs.lookup_still_valid) {
 822                 vm_object_t retry_object;
 823                 vm_pindex_t retry_pindex;
 824                 vm_prot_t retry_prot;
 825
 826                 if (!vm_map_trylock_read(fs.map)) {
 827                         release_page(&fs);
 828                         unlock_and_deallocate(&fs);
 829                         goto RetryFault;
 830                 }
 831                 fs.lookup_still_valid = TRUE;
 832                 if (fs.map->timestamp != map_generation) {
 833                         result = vm_map_lookup_locked(&fs.map, vaddr, fault_type,
 834                             &fs.entry, &retry_object, &retry_pindex, &retry_prot, &wired);
 835
 836                         /*
 837                          * If we don't need the page any longer, put it on the inactive
 838                          * list (the easiest thing to do here).  If no one needs it,
 839                          * pageout will grab it eventually.
 840                          */
 841                         if (result != KERN_SUCCESS) {
 842                                 release_page(&fs);
 843                                 unlock_and_deallocate(&fs);
 844
 845                                 /*
 846                                  * If retry of map lookup would have blocked then
 847                                  * retry fault from start.
 848                                  */
 849                                 if (result == KERN_FAILURE)
 850                                         goto RetryFault;
 851                                 return (result);
 852                         }
 853                         if ((retry_object != fs.first_object) ||
 854                             (retry_pindex != fs.first_pindex)) {
 855                                 release_page(&fs);
 856                                 unlock_and_deallocate(&fs);
 857                                 goto RetryFault;
 858                         }
 859
 860                         /*
 861                          * Check whether the protection has changed or the object has
 862                          * been copied while we left the map unlocked. Changing from
 863                          * read to write permission is OK - we leave the page
 864                          * write-protected, and catch the write fault. Changing from
 865                          * write to read permission means that we can't mark the page
 866                          * write-enabled after all.
 867                          */
 868                         prot &= retry_prot;
 869                 }
 870         }
 871         /*
 872          * If the page was filled by a pager, update the map entry's
 873          * last read offset.  Since the pager does not return the
 874          * actual set of pages that it read, this update is based on
 875          * the requested set.  Typically, the requested and actual
 876          * sets are the same.
 877          *
 878          * XXX The following assignment modifies the map
 879          * without holding a write lock on it.
 880          */
 881         if (hardfault)
 882                 fs.entry->lastr = fs.pindex + faultcount - behind;
 883
 884         if (prot & VM_PROT_WRITE) {
 885                 vm_object_set_writeable_dirty(fs.object);
 886
 887                 /*
 888                  * If the fault is a write, we know that this page is being
 889                  * written NOW so dirty it explicitly to save on
 890                  * pmap_is_modified() calls later.
 891                  *
 892                  * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
 893                  * if the page is already dirty to prevent data written with
 894                  * the expectation of being synced from not being synced.
 895                  * Likewise if this entry does not request NOSYNC then make
 896                  * sure the page isn't marked NOSYNC.  Applications sharing
 897                  * data should use the same flags to avoid ping ponging.
 898                  *
 899                  * Also tell the backing pager, if any, that it should remove
 900                  * any swap backing since the page is now dirty.
 901                  */
 902                 if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
 903                         if (fs.m->dirty == 0)
 904                                 fs.m->oflags |= VPO_NOSYNC;
 905                 } else {
 906                         fs.m->oflags &= ~VPO_NOSYNC;
 907                 }
 908                 if (fault_flags & VM_FAULT_DIRTY) {
 909                         vm_page_dirty(fs.m);
 910                         vm_pager_page_unswapped(fs.m);
 911                 }
 912         }
 913
 914         /*
 915          * Page had better still be busy
 916          */
 917         KASSERT(fs.m->oflags & VPO_BUSY,
 918                 ("vm_fault: page %p not busy!", fs.m));
 919         /*
 920          * Page must be completely valid or it is not fit to
 921          * map into user space.  vm_pager_get_pages() ensures this.
 922          */
 923         KASSERT(fs.m->valid == VM_PAGE_BITS_ALL,
 924             ("vm_fault: page %p partially invalid", fs.m));
 925         VM_OBJECT_UNLOCK(fs.object);
 926
 927         /*
 928          * Put this page into the physical map.  We had to do the unlock above
 929          * because pmap_enter() may sleep.  We don't put the page
 930          * back on the active queue until later so that the pageout daemon
 931          * won't find it (yet).
 932          */
 933         pmap_enter(fs.map->pmap, vaddr, fault_type, fs.m, prot, wired);
 934         if (((fault_flags & VM_FAULT_WIRE_MASK) == 0) && (wired == 0)) {
 935                 vm_fault_prefault(fs.map->pmap, vaddr, fs.entry);
 936         }
 937         VM_OBJECT_LOCK(fs.object);
 938         vm_page_lock_queues();
 939         vm_page_flag_set(fs.m, PG_REFERENCED);
 940
 941         /*
 942          * If the page is not wired down, then put it where the pageout daemon
 943          * can find it.
 944          */
 945         if (fault_flags & VM_FAULT_WIRE_MASK) {
 946                 if (wired)
 947                         vm_page_wire(fs.m);
 948                 else
 949                         vm_page_unwire(fs.m, 1);
 950         } else {
 951                 vm_page_activate(fs.m);
 952         }
 953         vm_page_unlock_queues();
 954         vm_page_wakeup(fs.m);
 955
 956         /*
 957          * Unlock everything, and return
 958          */
 959         unlock_and_deallocate(&fs);
 960         if (hardfault)
 961                 curthread->td_ru.ru_majflt++;
 962         else
 963                 curthread->td_ru.ru_minflt++;
 964
 965         return (KERN_SUCCESS);
 966 }
 967
 968 /*
 969  * vm_fault_prefault provides a quick way of clustering
 970  * pagefaults into a processes address space.  It is a "cousin"
 971  * of vm_map_pmap_enter, except it runs at page fault time instead
 972  * of mmap time.
 973  */
 974 static void
 975 vm_fault_prefault(pmap_t pmap, vm_offset_t addra, vm_map_entry_t entry)
 976 {
 977         int i;
 978         vm_offset_t addr, starta;
 979         vm_pindex_t pindex;
 980         vm_page_t m;
 981         vm_object_t object;
 982
 983         if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace))
 984                 return;
 985
 986         object = entry->object.vm_object;
 987
 988         starta = addra - PFBAK * PAGE_SIZE;
 989         if (starta < entry->start) {
 990                 starta = entry->start;
 991         } else if (starta > addra) {
 992                 starta = 0;
 993         }
 994
 995         for (i = 0; i < PAGEORDER_SIZE; i++) {
 996                 vm_object_t backing_object, lobject;
 997
 998                 addr = addra + prefault_pageorder[i];
 999                 if (addr > addra + (PFFOR * PAGE_SIZE))
1000                         addr = 0;
1001
1002                 if (addr < starta || addr >= entry->end)
1003                         continue;
1004
1005                 if (!pmap_is_prefaultable(pmap, addr))
1006                         continue;
1007
1008                 pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
1009                 lobject = object;
1010                 VM_OBJECT_LOCK(lobject);
1011                 while ((m = vm_page_lookup(lobject, pindex)) == NULL &&
1012                     lobject->type == OBJT_DEFAULT &&
1013                     (backing_object = lobject->backing_object) != NULL) {
1014                         if (lobject->backing_object_offset & PAGE_MASK)
1015                                 break;
1016                         pindex += lobject->backing_object_offset >> PAGE_SHIFT;
1017                         VM_OBJECT_LOCK(backing_object);
1018                         VM_OBJECT_UNLOCK(lobject);
1019                         lobject = backing_object;
1020                 }
1021                 /*
1022                  * give-up when a page is not in memory
1023                  */
1024                 if (m == NULL) {
1025                         VM_OBJECT_UNLOCK(lobject);
1026                         break;
1027                 }
1028                 if (m->valid == VM_PAGE_BITS_ALL &&
1029                     (m->flags & PG_FICTITIOUS) == 0) {
1030                         vm_page_lock_queues();
1031                         pmap_enter_quick(pmap, addr, m, entry->protection);
1032                         vm_page_unlock_queues();
1033                 }
1034                 VM_OBJECT_UNLOCK(lobject);
1035         }
1036 }
1037
1038 /*
1039  *      vm_fault_quick:
1040  *
1041  *      Ensure that the requested virtual address, which may be in userland,
1042  *      is valid.  Fault-in the page if necessary.  Return -1 on failure.
1043  */
1044 int
1045 vm_fault_quick(caddr_t v, int prot)
1046 {
1047         int r;
1048
1049         if (prot & VM_PROT_WRITE)
1050                 r = subyte(v, fubyte(v));
1051         else
1052                 r = fubyte(v);
1053         return(r);
1054 }
1055
1056 /*
1057  *      vm_fault_wire:
1058  *
1059  *      Wire down a range of virtual addresses in a map.
1060  */
1061 int
1062 vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1063     boolean_t user_wire, boolean_t fictitious)
1064 {
1065         vm_offset_t va;
1066         int rv;
1067
1068         /*
1069          * We simulate a fault to get the page and enter it in the physical
1070          * map.  For user wiring, we only ask for read access on currently
1071          * read-only sections.
1072          */
1073         for (va = start; va < end; va += PAGE_SIZE) {
1074                 rv = vm_fault(map, va,
1075                     user_wire ? VM_PROT_READ : VM_PROT_READ | VM_PROT_WRITE,
1076                     user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
1077                 if (rv) {
1078                         if (va != start)
1079                                 vm_fault_unwire(map, start, va, fictitious);
1080                         return (rv);
1081                 }
1082         }
1083         return (KERN_SUCCESS);
1084 }
1085
1086 /*
1087  *      vm_fault_unwire:
1088  *
1089  *      Unwire a range of virtual addresses in a map.
1090  */
1091 void
1092 vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
1093     boolean_t fictitious)
1094 {
1095         vm_paddr_t pa;
1096         vm_offset_t va;
1097         pmap_t pmap;
1098
1099         pmap = vm_map_pmap(map);
1100
1101         /*
1102          * Since the pages are wired down, we must be able to get their
1103          * mappings from the physical map system.
1104          */
1105         for (va = start; va < end; va += PAGE_SIZE) {
1106                 pa = pmap_extract(pmap, va);
1107                 if (pa != 0) {
1108                         pmap_change_wiring(pmap, va, FALSE);
1109                         if (!fictitious) {
1110                                 vm_page_lock_queues();
1111                                 vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
1112                                 vm_page_unlock_queues();
1113                         }
1114                 }
1115         }
1116 }
1117
1118 /*
1119  *      Routine:
1120  *              vm_fault_copy_entry
1121  *      Function:
1122  *              Copy all of the pages from a wired-down map entry to another.
1123  *
1124  *      In/out conditions:
1125  *              The source and destination maps must be locked for write.
1126  *              The source map entry must be wired down (or be a sharing map
1127  *              entry corresponding to a main map entry that is wired down).
1128  */
1129 void
1130 vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
1131     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
1132     vm_ooffset_t *fork_charge)
1133 {
1134         vm_object_t backing_object, dst_object, object;
1135         vm_object_t src_object;
1136         vm_ooffset_t dst_offset;
1137         vm_ooffset_t src_offset;
1138         vm_pindex_t pindex;
1139         vm_prot_t prot;
1140         vm_offset_t vaddr;
1141         vm_page_t dst_m;
1142         vm_page_t src_m;
1143
1144 #ifdef  lint
1145         src_map++;
1146 #endif  /* lint */
1147
1148         src_object = src_entry->object.vm_object;
1149         src_offset = src_entry->offset;
1150
1151         /*
1152          * Create the top-level object for the destination entry. (Doesn't
1153          * actually shadow anything - we copy the pages directly.)
1154          */
1155         dst_object = vm_object_allocate(OBJT_DEFAULT,
1156             OFF_TO_IDX(dst_entry->end - dst_entry->start));
1157 #if VM_NRESERVLEVEL > 0
1158         dst_object->flags |= OBJ_COLORED;
1159         dst_object->pg_color = atop(dst_entry->start);
1160 #endif
1161
1162         VM_OBJECT_LOCK(dst_object);
1163         KASSERT(dst_entry->object.vm_object == NULL,
1164             ("vm_fault_copy_entry: vm_object not NULL"));
1165         dst_entry->object.vm_object = dst_object;
1166         dst_entry->offset = 0;
1167         dst_object->uip = curthread->td_ucred->cr_ruidinfo;
1168         uihold(dst_object->uip);
1169         dst_object->charge = dst_entry->end - dst_entry->start;
1170         KASSERT(dst_entry->uip == NULL,
1171             ("vm_fault_copy_entry: leaked swp charge"));
1172         *fork_charge += dst_object->charge;
1173         prot = dst_entry->max_protection;
1174
1175         /*
1176          * Loop through all of the pages in the entry's range, copying each
1177          * one from the source object (it should be there) to the destination
1178          * object.
1179          */
1180         for (vaddr = dst_entry->start, dst_offset = 0;
1181             vaddr < dst_entry->end;
1182             vaddr += PAGE_SIZE, dst_offset += PAGE_SIZE) {
1183
1184                 /*
1185                  * Allocate a page in the destination object
1186                  */
1187                 do {
1188                         dst_m = vm_page_alloc(dst_object,
1189                                 OFF_TO_IDX(dst_offset), VM_ALLOC_NORMAL);
1190                         if (dst_m == NULL) {
1191                                 VM_OBJECT_UNLOCK(dst_object);
1192                                 VM_WAIT;
1193                                 VM_OBJECT_LOCK(dst_object);
1194                         }
1195                 } while (dst_m == NULL);
1196
1197                 /*
1198                  * Find the page in the source object, and copy it in.
1199                  * (Because the source is wired down, the page will be in
1200                  * memory.)
1201                  */
1202                 VM_OBJECT_LOCK(src_object);
1203                 object = src_object;
1204                 pindex = 0;
1205                 while ((src_m = vm_page_lookup(object, pindex +
1206                     OFF_TO_IDX(dst_offset + src_offset))) == NULL &&
1207                     (src_entry->protection & VM_PROT_WRITE) == 0 &&
1208                     (backing_object = object->backing_object) != NULL) {
1209                         /*
1210                          * Allow fallback to backing objects if we are reading.
1211                          */
1212                         VM_OBJECT_LOCK(backing_object);
1213                         pindex += OFF_TO_IDX(object->backing_object_offset);
1214                         VM_OBJECT_UNLOCK(object);
1215                         object = backing_object;
1216                 }
1217                 if (src_m == NULL)
1218                         panic("vm_fault_copy_wired: page missing");
1219                 pmap_copy_page(src_m, dst_m);
1220                 VM_OBJECT_UNLOCK(object);
1221                 dst_m->valid = VM_PAGE_BITS_ALL;
1222                 VM_OBJECT_UNLOCK(dst_object);
1223
1224                 /*
1225                  * Enter it in the pmap as a read and/or execute access.
1226                  */
1227                 pmap_enter(dst_map->pmap, vaddr, prot & ~VM_PROT_WRITE, dst_m,
1228                     prot, FALSE);
1229
1230                 /*
1231                  * Mark it no longer busy, and put it on the active list.
1232                  */
1233                 VM_OBJECT_LOCK(dst_object);
1234                 vm_page_lock_queues();
1235                 vm_page_activate(dst_m);
1236                 vm_page_unlock_queues();
1237                 vm_page_wakeup(dst_m);
1238         }
1239         VM_OBJECT_UNLOCK(dst_object);
1240 }
1241
1242
1243 /*
1244  * This routine checks around the requested page for other pages that
1245  * might be able to be faulted in.  This routine brackets the viable
1246  * pages for the pages to be paged in.
1247  *
1248  * Inputs:
1249  *      m, rbehind, rahead
1250  *
1251  * Outputs:
1252  *  marray (array of vm_page_t), reqpage (index of requested page)
1253  *
1254  * Return value:
1255  *  number of pages in marray
1256  */
1257 static int
1258 vm_fault_additional_pages(m, rbehind, rahead, marray, reqpage)
1259         vm_page_t m;
1260         int rbehind;
1261         int rahead;
1262         vm_page_t *marray;
1263         int *reqpage;
1264 {
1265         int i,j;
1266         vm_object_t object;
1267         vm_pindex_t pindex, startpindex, endpindex, tpindex;
1268         vm_page_t rtm;
1269         int cbehind, cahead;
1270
1271         VM_OBJECT_LOCK_ASSERT(m->object, MA_OWNED);
1272
1273         object = m->object;
1274         pindex = m->pindex;
1275         cbehind = cahead = 0;
1276
1277         /*
1278          * if the requested page is not available, then give up now
1279          */
1280         if (!vm_pager_has_page(object, pindex, &cbehind, &cahead)) {
1281                 return 0;
1282         }
1283
1284         if ((cbehind == 0) && (cahead == 0)) {
1285                 *reqpage = 0;
1286                 marray[0] = m;
1287                 return 1;
1288         }
1289
1290         if (rahead > cahead) {
1291                 rahead = cahead;
1292         }
1293
1294         if (rbehind > cbehind) {
1295                 rbehind = cbehind;
1296         }
1297
1298         /*
1299          * scan backward for the read behind pages -- in memory
1300          */
1301         if (pindex > 0) {
1302                 if (rbehind > pindex) {
1303                         rbehind = pindex;
1304                         startpindex = 0;
1305                 } else {
1306                         startpindex = pindex - rbehind;
1307                 }
1308
1309                 if ((rtm = TAILQ_PREV(m, pglist, listq)) != NULL &&
1310                     rtm->pindex >= startpindex)
1311                         startpindex = rtm->pindex + 1;
1312
1313                 /* tpindex is unsigned; beware of numeric underflow. */
1314                 for (i = 0, tpindex = pindex - 1; tpindex >= startpindex &&
1315                     tpindex < pindex; i++, tpindex--) {
1316
1317                         rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
1318                             VM_ALLOC_IFNOTCACHED);
1319                         if (rtm == NULL) {
1320                                 /*
1321                                  * Shift the allocated pages to the
1322                                  * beginning of the array.
1323                                  */
1324                                 for (j = 0; j < i; j++) {
1325                                         marray[j] = marray[j + tpindex + 1 -
1326                                             startpindex];
1327                                 }
1328                                 break;
1329                         }
1330
1331                         marray[tpindex - startpindex] = rtm;
1332                 }
1333         } else {
1334                 startpindex = 0;
1335                 i = 0;
1336         }
1337
1338         marray[i] = m;
1339         /* page offset of the required page */
1340         *reqpage = i;
1341
1342         tpindex = pindex + 1;
1343         i++;
1344
1345         /*
1346          * scan forward for the read ahead pages
1347          */
1348         endpindex = tpindex + rahead;
1349         if ((rtm = TAILQ_NEXT(m, listq)) != NULL && rtm->pindex < endpindex)
1350                 endpindex = rtm->pindex;
1351         if (endpindex > object->size)
1352                 endpindex = object->size;
1353
1354         for (; tpindex < endpindex; i++, tpindex++) {
1355
1356                 rtm = vm_page_alloc(object, tpindex, VM_ALLOC_NORMAL |
1357                     VM_ALLOC_IFNOTCACHED);
1358                 if (rtm == NULL) {
1359                         break;
1360                 }
1361
1362                 marray[i] = rtm;
1363         }
1364
1365         /* return number of pages */
1366         return i;
1367 }