sys/vm/vnode_pager.c

   1 /*-
   2  * Copyright (c) 1990 University of Utah.
   3  * Copyright (c) 1991 The Regents of the University of California.
   4  * All rights reserved.
   5  * Copyright (c) 1993, 1994 John S. Dyson
   6  * Copyright (c) 1995, David Greenman
   7  *
   8  * This code is derived from software contributed to Berkeley by
   9  * the Systems Programming Group of the University of Utah Computer
  10  * Science Department.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. All advertising materials mentioning features or use of this software
  21  *    must display the following acknowledgement:
  22  *      This product includes software developed by the University of
  23  *      California, Berkeley and its contributors.
  24  * 4. Neither the name of the University nor the names of its contributors
  25  *    may be used to endorse or promote products derived from this software
  26  *    without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  38  * SUCH DAMAGE.
  39  *
  40  *      from: @(#)vnode_pager.c 7.5 (Berkeley) 4/20/91
  41  */
  42
  43 /*
  44  * Page to/from files (vnodes).
  45  */
  46
  47 /*
  48  * TODO:
  49  *      Implement VOP_GETPAGES/PUTPAGES interface for filesystems. Will
  50  *      greatly re-simplify the vnode_pager.
  51  */
  52
  53 #include <sys/cdefs.h>
  54 __FBSDID("$FreeBSD$");
  55
  56 #include <sys/param.h>
  57 #include <sys/systm.h>
  58 #include <sys/proc.h>
  59 #include <sys/vnode.h>
  60 #include <sys/mount.h>
  61 #include <sys/bio.h>
  62 #include <sys/buf.h>
  63 #include <sys/vmmeter.h>
  64 #include <sys/limits.h>
  65 #include <sys/conf.h>
  66 #include <sys/rwlock.h>
  67 #include <sys/sf_buf.h>
  68
  69 #include <machine/atomic.h>
  70
  71 #include <vm/vm.h>
  72 #include <vm/vm_param.h>
  73 #include <vm/vm_object.h>
  74 #include <vm/vm_page.h>
  75 #include <vm/vm_pager.h>
  76 #include <vm/vm_map.h>
  77 #include <vm/vnode_pager.h>
  78 #include <vm/vm_extern.h>
  79
  80 static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
  81     daddr_t *rtaddress, int *run);
  82 static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
  83 static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
  84 static void vnode_pager_dealloc(vm_object_t);
  85 static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int);
  86 static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
  87 static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
  88 static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
  89     vm_ooffset_t, struct ucred *cred);
  90
  91 struct pagerops vnodepagerops = {
  92         .pgo_alloc =    vnode_pager_alloc,
  93         .pgo_dealloc =  vnode_pager_dealloc,
  94         .pgo_getpages = vnode_pager_getpages,
  95         .pgo_putpages = vnode_pager_putpages,
  96         .pgo_haspage =  vnode_pager_haspage,
  97 };
  98
  99 int vnode_pbuf_freecnt;
 100
 101 /* Create the VM system backing object for this vnode */
 102 int
 103 vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
 104 {
 105         vm_object_t object;
 106         vm_ooffset_t size = isize;
 107         struct vattr va;
 108
 109         if (!vn_isdisk(vp, NULL) && vn_canvmio(vp) == FALSE)
 110                 return (0);
 111
 112         while ((object = vp->v_object) != NULL) {
 113                 VM_OBJECT_WLOCK(object);
 114                 if (!(object->flags & OBJ_DEAD)) {
 115                         VM_OBJECT_WUNLOCK(object);
 116                         return (0);
 117                 }
 118                 VOP_UNLOCK(vp, 0);
 119                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 120                 VM_OBJECT_SLEEP(object, object, PDROP | PVM, "vodead", 0);
 121                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 122         }
 123
 124         if (size == 0) {
 125                 if (vn_isdisk(vp, NULL)) {
 126                         size = IDX_TO_OFF(INT_MAX);
 127                 } else {
 128                         if (VOP_GETATTR(vp, &va, td->td_ucred))
 129                                 return (0);
 130                         size = va.va_size;
 131                 }
 132         }
 133
 134         object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
 135         /*
 136          * Dereference the reference we just created.  This assumes
 137          * that the object is associated with the vp.
 138          */
 139         VM_OBJECT_WLOCK(object);
 140         object->ref_count--;
 141         VM_OBJECT_WUNLOCK(object);
 142         vrele(vp);
 143
 144         KASSERT(vp->v_object != NULL, ("vnode_create_vobject: NULL object"));
 145
 146         return (0);
 147 }
 148
 149 void
 150 vnode_destroy_vobject(struct vnode *vp)
 151 {
 152         struct vm_object *obj;
 153
 154         obj = vp->v_object;
 155         if (obj == NULL)
 156                 return;
 157         ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
 158         VM_OBJECT_WLOCK(obj);
 159         if (obj->ref_count == 0) {
 160                 /*
 161                  * don't double-terminate the object
 162                  */
 163                 if ((obj->flags & OBJ_DEAD) == 0)
 164                         vm_object_terminate(obj);
 165                 else
 166                         VM_OBJECT_WUNLOCK(obj);
 167         } else {
 168                 /*
 169                  * Woe to the process that tries to page now :-).
 170                  */
 171                 vm_pager_deallocate(obj);
 172                 VM_OBJECT_WUNLOCK(obj);
 173         }
 174         vp->v_object = NULL;
 175 }
 176
 177
 178 /*
 179  * Allocate (or lookup) pager for a vnode.
 180  * Handle is a vnode pointer.
 181  *
 182  * MPSAFE
 183  */
 184 vm_object_t
 185 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 186     vm_ooffset_t offset, struct ucred *cred)
 187 {
 188         vm_object_t object;
 189         struct vnode *vp;
 190
 191         /*
 192          * Pageout to vnode, no can do yet.
 193          */
 194         if (handle == NULL)
 195                 return (NULL);
 196
 197         vp = (struct vnode *) handle;
 198
 199         /*
 200          * If the object is being terminated, wait for it to
 201          * go away.
 202          */
 203 retry:
 204         while ((object = vp->v_object) != NULL) {
 205                 VM_OBJECT_WLOCK(object);
 206                 if ((object->flags & OBJ_DEAD) == 0)
 207                         break;
 208                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 209                 VM_OBJECT_SLEEP(object, object, PDROP | PVM, "vadead", 0);
 210         }
 211
 212         KASSERT(vp->v_usecount != 0, ("vnode_pager_alloc: no vnode reference"));
 213
 214         if (object == NULL) {
 215                 /*
 216                  * Add an object of the appropriate size
 217                  */
 218                 object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
 219
 220                 object->un_pager.vnp.vnp_size = size;
 221                 object->un_pager.vnp.writemappings = 0;
 222
 223                 object->handle = handle;
 224                 VI_LOCK(vp);
 225                 if (vp->v_object != NULL) {
 226                         /*
 227                          * Object has been created while we were sleeping
 228                          */
 229                         VI_UNLOCK(vp);
 230                         vm_object_destroy(object);
 231                         goto retry;
 232                 }
 233                 vp->v_object = object;
 234                 VI_UNLOCK(vp);
 235         } else {
 236                 object->ref_count++;
 237                 VM_OBJECT_WUNLOCK(object);
 238         }
 239         vref(vp);
 240         return (object);
 241 }
 242
 243 /*
 244  *      The object must be locked.
 245  */
 246 static void
 247 vnode_pager_dealloc(vm_object_t object)
 248 {
 249         struct vnode *vp;
 250         int refs;
 251
 252         vp = object->handle;
 253         if (vp == NULL)
 254                 panic("vnode_pager_dealloc: pager already dealloced");
 255
 256         VM_OBJECT_ASSERT_WLOCKED(object);
 257         vm_object_pip_wait(object, "vnpdea");
 258         refs = object->ref_count;
 259
 260         object->handle = NULL;
 261         object->type = OBJT_DEAD;
 262         if (object->flags & OBJ_DISCONNECTWNT) {
 263                 vm_object_clear_flag(object, OBJ_DISCONNECTWNT);
 264                 wakeup(object);
 265         }
 266         ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
 267         if (object->un_pager.vnp.writemappings > 0) {
 268                 object->un_pager.vnp.writemappings = 0;
 269                 VOP_ADD_WRITECOUNT(vp, -1);
 270                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
 271                     __func__, vp, vp->v_writecount);
 272         }
 273         vp->v_object = NULL;
 274         VOP_UNSET_TEXT(vp);
 275         VM_OBJECT_WUNLOCK(object);
 276         while (refs-- > 0)
 277                 vunref(vp);
 278         VM_OBJECT_WLOCK(object);
 279 }
 280
 281 static boolean_t
 282 vnode_pager_haspage(vm_object_t object, vm_pindex_t pindex, int *before,
 283     int *after)
 284 {
 285         struct vnode *vp = object->handle;
 286         daddr_t bn;
 287         int err;
 288         daddr_t reqblock;
 289         int poff;
 290         int bsize;
 291         int pagesperblock, blocksperpage;
 292
 293         VM_OBJECT_ASSERT_WLOCKED(object);
 294         /*
 295          * If no vp or vp is doomed or marked transparent to VM, we do not
 296          * have the page.
 297          */
 298         if (vp == NULL || vp->v_iflag & VI_DOOMED)
 299                 return FALSE;
 300         /*
 301          * If the offset is beyond end of file we do
 302          * not have the page.
 303          */
 304         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
 305                 return FALSE;
 306
 307         bsize = vp->v_mount->mnt_stat.f_iosize;
 308         pagesperblock = bsize / PAGE_SIZE;
 309         blocksperpage = 0;
 310         if (pagesperblock > 0) {
 311                 reqblock = pindex / pagesperblock;
 312         } else {
 313                 blocksperpage = (PAGE_SIZE / bsize);
 314                 reqblock = pindex * blocksperpage;
 315         }
 316         VM_OBJECT_WUNLOCK(object);
 317         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
 318         VM_OBJECT_WLOCK(object);
 319         if (err)
 320                 return TRUE;
 321         if (bn == -1)
 322                 return FALSE;
 323         if (pagesperblock > 0) {
 324                 poff = pindex - (reqblock * pagesperblock);
 325                 if (before) {
 326                         *before *= pagesperblock;
 327                         *before += poff;
 328                 }
 329                 if (after) {
 330                         int numafter;
 331                         *after *= pagesperblock;
 332                         numafter = pagesperblock - (poff + 1);
 333                         if (IDX_TO_OFF(pindex + numafter) >
 334                             object->un_pager.vnp.vnp_size) {
 335                                 numafter =
 336                                     OFF_TO_IDX(object->un_pager.vnp.vnp_size) -
 337                                     pindex;
 338                         }
 339                         *after += numafter;
 340                 }
 341         } else {
 342                 if (before) {
 343                         *before /= blocksperpage;
 344                 }
 345
 346                 if (after) {
 347                         *after /= blocksperpage;
 348                 }
 349         }
 350         return TRUE;
 351 }
 352
 353 /*
 354  * Lets the VM system know about a change in size for a file.
 355  * We adjust our own internal size and flush any cached pages in
 356  * the associated object that are affected by the size change.
 357  *
 358  * Note: this routine may be invoked as a result of a pager put
 359  * operation (possibly at object termination time), so we must be careful.
 360  */
 361 void
 362 vnode_pager_setsize(struct vnode *vp, vm_ooffset_t nsize)
 363 {
 364         vm_object_t object;
 365         vm_page_t m;
 366         vm_pindex_t nobjsize;
 367
 368         if ((object = vp->v_object) == NULL)
 369                 return;
 370 /*      ASSERT_VOP_ELOCKED(vp, "vnode_pager_setsize and not locked vnode"); */
 371         VM_OBJECT_WLOCK(object);
 372         if (object->type == OBJT_DEAD) {
 373                 VM_OBJECT_WUNLOCK(object);
 374                 return;
 375         }
 376         KASSERT(object->type == OBJT_VNODE,
 377             ("not vnode-backed object %p", object));
 378         if (nsize == object->un_pager.vnp.vnp_size) {
 379                 /*
 380                  * Hasn't changed size
 381                  */
 382                 VM_OBJECT_WUNLOCK(object);
 383                 return;
 384         }
 385         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
 386         if (nsize < object->un_pager.vnp.vnp_size) {
 387                 /*
 388                  * File has shrunk. Toss any cached pages beyond the new EOF.
 389                  */
 390                 if (nobjsize < object->size)
 391                         vm_object_page_remove(object, nobjsize, object->size,
 392                             0);
 393                 /*
 394                  * this gets rid of garbage at the end of a page that is now
 395                  * only partially backed by the vnode.
 396                  *
 397                  * XXX for some reason (I don't know yet), if we take a
 398                  * completely invalid page and mark it partially valid
 399                  * it can screw up NFS reads, so we don't allow the case.
 400                  */
 401                 if ((nsize & PAGE_MASK) &&
 402                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
 403                     m->valid != 0) {
 404                         int base = (int)nsize & PAGE_MASK;
 405                         int size = PAGE_SIZE - base;
 406
 407                         /*
 408                          * Clear out partial-page garbage in case
 409                          * the page has been mapped.
 410                          */
 411                         pmap_zero_page_area(m, base, size);
 412
 413                         /*
 414                          * Update the valid bits to reflect the blocks that
 415                          * have been zeroed.  Some of these valid bits may
 416                          * have already been set.
 417                          */
 418                         vm_page_set_valid_range(m, base, size);
 419
 420                         /*
 421                          * Round "base" to the next block boundary so that the
 422                          * dirty bit for a partially zeroed block is not
 423                          * cleared.
 424                          */
 425                         base = roundup2(base, DEV_BSIZE);
 426
 427                         /*
 428                          * Clear out partial-page dirty bits.
 429                          *
 430                          * note that we do not clear out the valid
 431                          * bits.  This would prevent bogus_page
 432                          * replacement from working properly.
 433                          */
 434                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
 435                 } else if ((nsize & PAGE_MASK) &&
 436                     vm_page_is_cached(object, OFF_TO_IDX(nsize))) {
 437                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
 438                             nobjsize);
 439                 }
 440         }
 441         object->un_pager.vnp.vnp_size = nsize;
 442         object->size = nobjsize;
 443         VM_OBJECT_WUNLOCK(object);
 444 }
 445
 446 /*
 447  * calculate the linear (byte) disk address of specified virtual
 448  * file address
 449  */
 450 static int
 451 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
 452     int *run)
 453 {
 454         int bsize;
 455         int err;
 456         daddr_t vblock;
 457         daddr_t voffset;
 458
 459         if (address < 0)
 460                 return -1;
 461
 462         if (vp->v_iflag & VI_DOOMED)
 463                 return -1;
 464
 465         bsize = vp->v_mount->mnt_stat.f_iosize;
 466         vblock = address / bsize;
 467         voffset = address % bsize;
 468
 469         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
 470         if (err == 0) {
 471                 if (*rtaddress != -1)
 472                         *rtaddress += voffset / DEV_BSIZE;
 473                 if (run) {
 474                         *run += 1;
 475                         *run *= bsize/PAGE_SIZE;
 476                         *run -= voffset/PAGE_SIZE;
 477                 }
 478         }
 479
 480         return (err);
 481 }
 482
 483 /*
 484  * small block filesystem vnode pager input
 485  */
 486 static int
 487 vnode_pager_input_smlfs(vm_object_t object, vm_page_t m)
 488 {
 489         struct vnode *vp;
 490         struct bufobj *bo;
 491         struct buf *bp;
 492         struct sf_buf *sf;
 493         daddr_t fileaddr;
 494         vm_offset_t bsize;
 495         vm_page_bits_t bits;
 496         int error, i;
 497
 498         error = 0;
 499         vp = object->handle;
 500         if (vp->v_iflag & VI_DOOMED)
 501                 return VM_PAGER_BAD;
 502
 503         bsize = vp->v_mount->mnt_stat.f_iosize;
 504
 505         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
 506
 507         sf = sf_buf_alloc(m, 0);
 508
 509         for (i = 0; i < PAGE_SIZE / bsize; i++) {
 510                 vm_ooffset_t address;
 511
 512                 bits = vm_page_bits(i * bsize, bsize);
 513                 if (m->valid & bits)
 514                         continue;
 515
 516                 address = IDX_TO_OFF(m->pindex) + i * bsize;
 517                 if (address >= object->un_pager.vnp.vnp_size) {
 518                         fileaddr = -1;
 519                 } else {
 520                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
 521                         if (error)
 522                                 break;
 523                 }
 524                 if (fileaddr != -1) {
 525                         bp = getpbuf(&vnode_pbuf_freecnt);
 526
 527                         /* build a minimal buffer header */
 528                         bp->b_iocmd = BIO_READ;
 529                         bp->b_iodone = bdone;
 530                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 531                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 532                         bp->b_rcred = crhold(curthread->td_ucred);
 533                         bp->b_wcred = crhold(curthread->td_ucred);
 534                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
 535                         bp->b_blkno = fileaddr;
 536                         pbgetbo(bo, bp);
 537                         bp->b_vp = vp;
 538                         bp->b_bcount = bsize;
 539                         bp->b_bufsize = bsize;
 540                         bp->b_runningbufspace = bp->b_bufsize;
 541                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 542
 543                         /* do the input */
 544                         bp->b_iooffset = dbtob(bp->b_blkno);
 545                         bstrategy(bp);
 546
 547                         bwait(bp, PVM, "vnsrd");
 548
 549                         if ((bp->b_ioflags & BIO_ERROR) != 0)
 550                                 error = EIO;
 551
 552                         /*
 553                          * free the buffer header back to the swap buffer pool
 554                          */
 555                         bp->b_vp = NULL;
 556                         pbrelbo(bp);
 557                         relpbuf(bp, &vnode_pbuf_freecnt);
 558                         if (error)
 559                                 break;
 560                 } else
 561                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
 562                 KASSERT((m->dirty & bits) == 0,
 563                     ("vnode_pager_input_smlfs: page %p is dirty", m));
 564                 VM_OBJECT_WLOCK(object);
 565                 m->valid |= bits;
 566                 VM_OBJECT_WUNLOCK(object);
 567         }
 568         sf_buf_free(sf);
 569         if (error) {
 570                 return VM_PAGER_ERROR;
 571         }
 572         return VM_PAGER_OK;
 573 }
 574
 575 /*
 576  * old style vnode pager input routine
 577  */
 578 static int
 579 vnode_pager_input_old(vm_object_t object, vm_page_t m)
 580 {
 581         struct uio auio;
 582         struct iovec aiov;
 583         int error;
 584         int size;
 585         struct sf_buf *sf;
 586         struct vnode *vp;
 587
 588         VM_OBJECT_ASSERT_WLOCKED(object);
 589         error = 0;
 590
 591         /*
 592          * Return failure if beyond current EOF
 593          */
 594         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
 595                 return VM_PAGER_BAD;
 596         } else {
 597                 size = PAGE_SIZE;
 598                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
 599                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
 600                 vp = object->handle;
 601                 VM_OBJECT_WUNLOCK(object);
 602
 603                 /*
 604                  * Allocate a kernel virtual address and initialize so that
 605                  * we can use VOP_READ/WRITE routines.
 606                  */
 607                 sf = sf_buf_alloc(m, 0);
 608
 609                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
 610                 aiov.iov_len = size;
 611                 auio.uio_iov = &aiov;
 612                 auio.uio_iovcnt = 1;
 613                 auio.uio_offset = IDX_TO_OFF(m->pindex);
 614                 auio.uio_segflg = UIO_SYSSPACE;
 615                 auio.uio_rw = UIO_READ;
 616                 auio.uio_resid = size;
 617                 auio.uio_td = curthread;
 618
 619                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
 620                 if (!error) {
 621                         int count = size - auio.uio_resid;
 622
 623                         if (count == 0)
 624                                 error = EINVAL;
 625                         else if (count != PAGE_SIZE)
 626                                 bzero((caddr_t)sf_buf_kva(sf) + count,
 627                                     PAGE_SIZE - count);
 628                 }
 629                 sf_buf_free(sf);
 630
 631                 VM_OBJECT_WLOCK(object);
 632         }
 633         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
 634         if (!error)
 635                 m->valid = VM_PAGE_BITS_ALL;
 636         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
 637 }
 638
 639 /*
 640  * generic vnode pager input routine
 641  */
 642
 643 /*
 644  * Local media VFS's that do not implement their own VOP_GETPAGES
 645  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 646  * to implement the previous behaviour.
 647  *
 648  * All other FS's should use the bypass to get to the local media
 649  * backing vp's VOP_GETPAGES.
 650  */
 651 static int
 652 vnode_pager_getpages(vm_object_t object, vm_page_t *m, int count, int reqpage)
 653 {
 654         int rtval;
 655         struct vnode *vp;
 656         int bytes = count * PAGE_SIZE;
 657
 658         vp = object->handle;
 659         VM_OBJECT_WUNLOCK(object);
 660         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
 661         KASSERT(rtval != EOPNOTSUPP,
 662             ("vnode_pager: FS getpages not implemented\n"));
 663         VM_OBJECT_WLOCK(object);
 664         return rtval;
 665 }
 666
 667 /*
 668  * This is now called from local media FS's to operate against their
 669  * own vnodes if they fail to implement VOP_GETPAGES.
 670  */
 671 int
 672 vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int bytecount,
 673     int reqpage)
 674 {
 675         vm_object_t object;
 676         vm_offset_t kva;
 677         off_t foff, tfoff, nextoff;
 678         int i, j, size, bsize, first;
 679         daddr_t firstaddr, reqblock;
 680         struct bufobj *bo;
 681         int runpg;
 682         int runend;
 683         struct buf *bp;
 684         struct mount *mp;
 685         int count;
 686         int error;
 687
 688         object = vp->v_object;
 689         count = bytecount / PAGE_SIZE;
 690
 691         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
 692             ("vnode_pager_generic_getpages does not support devices"));
 693         if (vp->v_iflag & VI_DOOMED)
 694                 return VM_PAGER_BAD;
 695
 696         bsize = vp->v_mount->mnt_stat.f_iosize;
 697
 698         /* get the UNDERLYING device for the file with VOP_BMAP() */
 699
 700         /*
 701          * originally, we did not check for an error return value -- assuming
 702          * an fs always has a bmap entry point -- that assumption is wrong!!!
 703          */
 704         foff = IDX_TO_OFF(m[reqpage]->pindex);
 705
 706         /*
 707          * if we can't bmap, use old VOP code
 708          */
 709         error = VOP_BMAP(vp, foff / bsize, &bo, &reqblock, NULL, NULL);
 710         if (error == EOPNOTSUPP) {
 711                 VM_OBJECT_WLOCK(object);
 712
 713                 for (i = 0; i < count; i++)
 714                         if (i != reqpage) {
 715                                 vm_page_lock(m[i]);
 716                                 vm_page_free(m[i]);
 717                                 vm_page_unlock(m[i]);
 718                         }
 719                 PCPU_INC(cnt.v_vnodein);
 720                 PCPU_INC(cnt.v_vnodepgsin);
 721                 error = vnode_pager_input_old(object, m[reqpage]);
 722                 VM_OBJECT_WUNLOCK(object);
 723                 return (error);
 724         } else if (error != 0) {
 725                 VM_OBJECT_WLOCK(object);
 726                 for (i = 0; i < count; i++)
 727                         if (i != reqpage) {
 728                                 vm_page_lock(m[i]);
 729                                 vm_page_free(m[i]);
 730                                 vm_page_unlock(m[i]);
 731                         }
 732                 VM_OBJECT_WUNLOCK(object);
 733                 return (VM_PAGER_ERROR);
 734
 735                 /*
 736                  * if the blocksize is smaller than a page size, then use
 737                  * special small filesystem code.  NFS sometimes has a small
 738                  * blocksize, but it can handle large reads itself.
 739                  */
 740         } else if ((PAGE_SIZE / bsize) > 1 &&
 741             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
 742                 VM_OBJECT_WLOCK(object);
 743                 for (i = 0; i < count; i++)
 744                         if (i != reqpage) {
 745                                 vm_page_lock(m[i]);
 746                                 vm_page_free(m[i]);
 747                                 vm_page_unlock(m[i]);
 748                         }
 749                 VM_OBJECT_WUNLOCK(object);
 750                 PCPU_INC(cnt.v_vnodein);
 751                 PCPU_INC(cnt.v_vnodepgsin);
 752                 return vnode_pager_input_smlfs(object, m[reqpage]);
 753         }
 754
 755         /*
 756          * If we have a completely valid page available to us, we can
 757          * clean up and return.  Otherwise we have to re-read the
 758          * media.
 759          */
 760         VM_OBJECT_WLOCK(object);
 761         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
 762                 for (i = 0; i < count; i++)
 763                         if (i != reqpage) {
 764                                 vm_page_lock(m[i]);
 765                                 vm_page_free(m[i]);
 766                                 vm_page_unlock(m[i]);
 767                         }
 768                 VM_OBJECT_WUNLOCK(object);
 769                 return VM_PAGER_OK;
 770         } else if (reqblock == -1) {
 771                 pmap_zero_page(m[reqpage]);
 772                 KASSERT(m[reqpage]->dirty == 0,
 773                     ("vnode_pager_generic_getpages: page %p is dirty", m));
 774                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
 775                 for (i = 0; i < count; i++)
 776                         if (i != reqpage) {
 777                                 vm_page_lock(m[i]);
 778                                 vm_page_free(m[i]);
 779                                 vm_page_unlock(m[i]);
 780                         }
 781                 VM_OBJECT_WUNLOCK(object);
 782                 return (VM_PAGER_OK);
 783         }
 784         m[reqpage]->valid = 0;
 785         VM_OBJECT_WUNLOCK(object);
 786
 787         /*
 788          * here on direct device I/O
 789          */
 790         firstaddr = -1;
 791
 792         /*
 793          * calculate the run that includes the required page
 794          */
 795         for (first = 0, i = 0; i < count; i = runend) {
 796                 if (vnode_pager_addr(vp, IDX_TO_OFF(m[i]->pindex), &firstaddr,
 797                     &runpg) != 0) {
 798                         VM_OBJECT_WLOCK(object);
 799                         for (; i < count; i++)
 800                                 if (i != reqpage) {
 801                                         vm_page_lock(m[i]);
 802                                         vm_page_free(m[i]);
 803                                         vm_page_unlock(m[i]);
 804                                 }
 805                         VM_OBJECT_WUNLOCK(object);
 806                         return (VM_PAGER_ERROR);
 807                 }
 808                 if (firstaddr == -1) {
 809                         VM_OBJECT_WLOCK(object);
 810                         if (i == reqpage && foff < object->un_pager.vnp.vnp_size) {
 811                                 panic("vnode_pager_getpages: unexpected missing page: firstaddr: %jd, foff: 0x%jx%08jx, vnp_size: 0x%jx%08jx",
 812                                     (intmax_t)firstaddr, (uintmax_t)(foff >> 32),
 813                                     (uintmax_t)foff,
 814                                     (uintmax_t)
 815                                     (object->un_pager.vnp.vnp_size >> 32),
 816                                     (uintmax_t)object->un_pager.vnp.vnp_size);
 817                         }
 818                         vm_page_lock(m[i]);
 819                         vm_page_free(m[i]);
 820                         vm_page_unlock(m[i]);
 821                         VM_OBJECT_WUNLOCK(object);
 822                         runend = i + 1;
 823                         first = runend;
 824                         continue;
 825                 }
 826                 runend = i + runpg;
 827                 if (runend <= reqpage) {
 828                         VM_OBJECT_WLOCK(object);
 829                         for (j = i; j < runend; j++) {
 830                                 vm_page_lock(m[j]);
 831                                 vm_page_free(m[j]);
 832                                 vm_page_unlock(m[j]);
 833                         }
 834                         VM_OBJECT_WUNLOCK(object);
 835                 } else {
 836                         if (runpg < (count - first)) {
 837                                 VM_OBJECT_WLOCK(object);
 838                                 for (i = first + runpg; i < count; i++) {
 839                                         vm_page_lock(m[i]);
 840                                         vm_page_free(m[i]);
 841                                         vm_page_unlock(m[i]);
 842                                 }
 843                                 VM_OBJECT_WUNLOCK(object);
 844                                 count = first + runpg;
 845                         }
 846                         break;
 847                 }
 848                 first = runend;
 849         }
 850
 851         /*
 852          * the first and last page have been calculated now, move input pages
 853          * to be zero based...
 854          */
 855         if (first != 0) {
 856                 m += first;
 857                 count -= first;
 858                 reqpage -= first;
 859         }
 860
 861         /*
 862          * calculate the file virtual address for the transfer
 863          */
 864         foff = IDX_TO_OFF(m[0]->pindex);
 865
 866         /*
 867          * calculate the size of the transfer
 868          */
 869         size = count * PAGE_SIZE;
 870         KASSERT(count > 0, ("zero count"));
 871         if ((foff + size) > object->un_pager.vnp.vnp_size)
 872                 size = object->un_pager.vnp.vnp_size - foff;
 873         KASSERT(size > 0, ("zero size"));
 874
 875         /*
 876          * round up physical size for real devices.
 877          */
 878         if (1) {
 879                 int secmask = bo->bo_bsize - 1;
 880                 KASSERT(secmask < PAGE_SIZE && secmask > 0,
 881                     ("vnode_pager_generic_getpages: sector size %d too large",
 882                     secmask + 1));
 883                 size = (size + secmask) & ~secmask;
 884         }
 885
 886         bp = getpbuf(&vnode_pbuf_freecnt);
 887         kva = (vm_offset_t)bp->b_data;
 888
 889         /*
 890          * and map the pages to be read into the kva, if the filesystem
 891          * requires mapped buffers.
 892          */
 893         mp = vp->v_mount;
 894         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0 &&
 895             unmapped_buf_allowed) {
 896                 bp->b_data = unmapped_buf;
 897                 bp->b_kvabase = unmapped_buf;
 898                 bp->b_offset = 0;
 899                 bp->b_flags |= B_UNMAPPED;
 900                 bp->b_npages = count;
 901                 for (i = 0; i < count; i++)
 902                         bp->b_pages[i] = m[i];
 903         } else
 904                 pmap_qenter(kva, m, count);
 905
 906         /* build a minimal buffer header */
 907         bp->b_iocmd = BIO_READ;
 908         bp->b_iodone = bdone;
 909         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 910         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 911         bp->b_rcred = crhold(curthread->td_ucred);
 912         bp->b_wcred = crhold(curthread->td_ucred);
 913         bp->b_blkno = firstaddr;
 914         pbgetbo(bo, bp);
 915         bp->b_vp = vp;
 916         bp->b_bcount = size;
 917         bp->b_bufsize = size;
 918         bp->b_runningbufspace = bp->b_bufsize;
 919         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 920
 921         PCPU_INC(cnt.v_vnodein);
 922         PCPU_ADD(cnt.v_vnodepgsin, count);
 923
 924         /* do the input */
 925         bp->b_iooffset = dbtob(bp->b_blkno);
 926         bstrategy(bp);
 927
 928         bwait(bp, PVM, "vnread");
 929
 930         if ((bp->b_ioflags & BIO_ERROR) != 0)
 931                 error = EIO;
 932
 933         if (error == 0 && size != count * PAGE_SIZE) {
 934                 if ((bp->b_flags & B_UNMAPPED) != 0) {
 935                         bp->b_flags &= ~B_UNMAPPED;
 936                         pmap_qenter(kva, m, count);
 937                 }
 938                 bzero((caddr_t)kva + size, PAGE_SIZE * count - size);
 939         }
 940         if ((bp->b_flags & B_UNMAPPED) == 0)
 941                 pmap_qremove(kva, count);
 942         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0) {
 943                 bp->b_data = (caddr_t)kva;
 944                 bp->b_kvabase = (caddr_t)kva;
 945                 bp->b_flags &= ~B_UNMAPPED;
 946                 for (i = 0; i < count; i++)
 947                         bp->b_pages[i] = NULL;
 948         }
 949
 950         /*
 951          * free the buffer header back to the swap buffer pool
 952          */
 953         bp->b_vp = NULL;
 954         pbrelbo(bp);
 955         relpbuf(bp, &vnode_pbuf_freecnt);
 956
 957         VM_OBJECT_WLOCK(object);
 958         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
 959                 vm_page_t mt;
 960
 961                 nextoff = tfoff + PAGE_SIZE;
 962                 mt = m[i];
 963
 964                 if (nextoff <= object->un_pager.vnp.vnp_size) {
 965                         /*
 966                          * Read filled up entire page.
 967                          */
 968                         mt->valid = VM_PAGE_BITS_ALL;
 969                         KASSERT(mt->dirty == 0,
 970                             ("vnode_pager_generic_getpages: page %p is dirty",
 971                             mt));
 972                         KASSERT(!pmap_page_is_mapped(mt),
 973                             ("vnode_pager_generic_getpages: page %p is mapped",
 974                             mt));
 975                 } else {
 976                         /*
 977                          * Read did not fill up entire page.
 978                          *
 979                          * Currently we do not set the entire page valid,
 980                          * we just try to clear the piece that we couldn't
 981                          * read.
 982                          */
 983                         vm_page_set_valid_range(mt, 0,
 984                             object->un_pager.vnp.vnp_size - tfoff);
 985                         KASSERT((mt->dirty & vm_page_bits(0,
 986                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
 987                             ("vnode_pager_generic_getpages: page %p is dirty",
 988                             mt));
 989                 }
 990
 991                 if (i != reqpage)
 992                         vm_page_readahead_finish(mt);
 993         }
 994         VM_OBJECT_WUNLOCK(object);
 995         if (error) {
 996                 printf("vnode_pager_getpages: I/O read error\n");
 997         }
 998         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
 999 }
1000
1001 /*
1002  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
1003  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
1004  * vnode_pager_generic_putpages() to implement the previous behaviour.
1005  *
1006  * All other FS's should use the bypass to get to the local media
1007  * backing vp's VOP_PUTPAGES.
1008  */
1009 static void
1010 vnode_pager_putpages(vm_object_t object, vm_page_t *m, int count,
1011     boolean_t sync, int *rtvals)
1012 {
1013         int rtval;
1014         struct vnode *vp;
1015         int bytes = count * PAGE_SIZE;
1016
1017         /*
1018          * Force synchronous operation if we are extremely low on memory
1019          * to prevent a low-memory deadlock.  VOP operations often need to
1020          * allocate more memory to initiate the I/O ( i.e. do a BMAP
1021          * operation ).  The swapper handles the case by limiting the amount
1022          * of asynchronous I/O, but that sort of solution doesn't scale well
1023          * for the vnode pager without a lot of work.
1024          *
1025          * Also, the backing vnode's iodone routine may not wake the pageout
1026          * daemon up.  This should be probably be addressed XXX.
1027          */
1028
1029         if ((vm_cnt.v_free_count + vm_cnt.v_cache_count) <
1030             vm_cnt.v_pageout_free_min)
1031                 sync |= OBJPC_SYNC;
1032
1033         /*
1034          * Call device-specific putpages function
1035          */
1036         vp = object->handle;
1037         VM_OBJECT_WUNLOCK(object);
1038         rtval = VOP_PUTPAGES(vp, m, bytes, sync, rtvals, 0);
1039         KASSERT(rtval != EOPNOTSUPP,
1040             ("vnode_pager: stale FS putpages\n"));
1041         VM_OBJECT_WLOCK(object);
1042 }
1043
1044
1045 /*
1046  * This is now called from local media FS's to operate against their
1047  * own vnodes if they fail to implement VOP_PUTPAGES.
1048  *
1049  * This is typically called indirectly via the pageout daemon and
1050  * clustering has already typically occured, so in general we ask the
1051  * underlying filesystem to write the data out asynchronously rather
1052  * then delayed.
1053  */
1054 int
1055 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
1056     int flags, int *rtvals)
1057 {
1058         int i;
1059         vm_object_t object;
1060         vm_page_t m;
1061         int count;
1062
1063         int maxsize, ncount;
1064         vm_ooffset_t poffset;
1065         struct uio auio;
1066         struct iovec aiov;
1067         int error;
1068         int ioflags;
1069         int ppscheck = 0;
1070         static struct timeval lastfail;
1071         static int curfail;
1072
1073         object = vp->v_object;
1074         count = bytecount / PAGE_SIZE;
1075
1076         for (i = 0; i < count; i++)
1077                 rtvals[i] = VM_PAGER_ERROR;
1078
1079         if ((int64_t)ma[0]->pindex < 0) {
1080                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
1081                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
1082                 rtvals[0] = VM_PAGER_BAD;
1083                 return VM_PAGER_BAD;
1084         }
1085
1086         maxsize = count * PAGE_SIZE;
1087         ncount = count;
1088
1089         poffset = IDX_TO_OFF(ma[0]->pindex);
1090
1091         /*
1092          * If the page-aligned write is larger then the actual file we
1093          * have to invalidate pages occuring beyond the file EOF.  However,
1094          * there is an edge case where a file may not be page-aligned where
1095          * the last page is partially invalid.  In this case the filesystem
1096          * may not properly clear the dirty bits for the entire page (which
1097          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
1098          * With the page locked we are free to fix-up the dirty bits here.
1099          *
1100          * We do not under any circumstances truncate the valid bits, as
1101          * this will screw up bogus page replacement.
1102          */
1103         VM_OBJECT_WLOCK(object);
1104         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
1105                 if (object->un_pager.vnp.vnp_size > poffset) {
1106                         int pgoff;
1107
1108                         maxsize = object->un_pager.vnp.vnp_size - poffset;
1109                         ncount = btoc(maxsize);
1110                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
1111                                 /*
1112                                  * If the object is locked and the following
1113                                  * conditions hold, then the page's dirty
1114                                  * field cannot be concurrently changed by a
1115                                  * pmap operation.
1116                                  */
1117                                 m = ma[ncount - 1];
1118                                 vm_page_assert_sbusied(m);
1119                                 KASSERT(!pmap_page_is_write_mapped(m),
1120                 ("vnode_pager_generic_putpages: page %p is not read-only", m));
1121                                 vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
1122                                     pgoff);
1123                         }
1124                 } else {
1125                         maxsize = 0;
1126                         ncount = 0;
1127                 }
1128                 if (ncount < count) {
1129                         for (i = ncount; i < count; i++) {
1130                                 rtvals[i] = VM_PAGER_BAD;
1131                         }
1132                 }
1133         }
1134         VM_OBJECT_WUNLOCK(object);
1135
1136         /*
1137          * pageouts are already clustered, use IO_ASYNC to force a bawrite()
1138          * rather then a bdwrite() to prevent paging I/O from saturating
1139          * the buffer cache.  Dummy-up the sequential heuristic to cause
1140          * large ranges to cluster.  If neither IO_SYNC or IO_ASYNC is set,
1141          * the system decides how to cluster.
1142          */
1143         ioflags = IO_VMIO;
1144         if (flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL))
1145                 ioflags |= IO_SYNC;
1146         else if ((flags & VM_PAGER_CLUSTER_OK) == 0)
1147                 ioflags |= IO_ASYNC;
1148         ioflags |= (flags & VM_PAGER_PUT_INVAL) ? IO_INVAL: 0;
1149         ioflags |= IO_SEQMAX << IO_SEQSHIFT;
1150
1151         aiov.iov_base = (caddr_t) 0;
1152         aiov.iov_len = maxsize;
1153         auio.uio_iov = &aiov;
1154         auio.uio_iovcnt = 1;
1155         auio.uio_offset = poffset;
1156         auio.uio_segflg = UIO_NOCOPY;
1157         auio.uio_rw = UIO_WRITE;
1158         auio.uio_resid = maxsize;
1159         auio.uio_td = (struct thread *) 0;
1160         error = VOP_WRITE(vp, &auio, ioflags, curthread->td_ucred);
1161         PCPU_INC(cnt.v_vnodeout);
1162         PCPU_ADD(cnt.v_vnodepgsout, ncount);
1163
1164         if (error) {
1165                 if ((ppscheck = ppsratecheck(&lastfail, &curfail, 1)))
1166                         printf("vnode_pager_putpages: I/O error %d\n", error);
1167         }
1168         if (auio.uio_resid) {
1169                 if (ppscheck || ppsratecheck(&lastfail, &curfail, 1))
1170                         printf("vnode_pager_putpages: residual I/O %zd at %lu\n",
1171                             auio.uio_resid, (u_long)ma[0]->pindex);
1172         }
1173         for (i = 0; i < ncount; i++) {
1174                 rtvals[i] = VM_PAGER_OK;
1175         }
1176         return rtvals[0];
1177 }
1178
1179 void
1180 vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
1181 {
1182         vm_object_t obj;
1183         int i, pos;
1184
1185         if (written == 0)
1186                 return;
1187         obj = ma[0]->object;
1188         VM_OBJECT_WLOCK(obj);
1189         for (i = 0, pos = 0; pos < written; i++, pos += PAGE_SIZE) {
1190                 if (pos < trunc_page(written)) {
1191                         rtvals[i] = VM_PAGER_OK;
1192                         vm_page_undirty(ma[i]);
1193                 } else {
1194                         /* Partially written page. */
1195                         rtvals[i] = VM_PAGER_AGAIN;
1196                         vm_page_clear_dirty(ma[i], 0, written & PAGE_MASK);
1197                 }
1198         }
1199         VM_OBJECT_WUNLOCK(obj);
1200 }
1201
1202 void
1203 vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
1204     vm_offset_t end)
1205 {
1206         struct vnode *vp;
1207         vm_ooffset_t old_wm;
1208
1209         VM_OBJECT_WLOCK(object);
1210         if (object->type != OBJT_VNODE) {
1211                 VM_OBJECT_WUNLOCK(object);
1212                 return;
1213         }
1214         old_wm = object->un_pager.vnp.writemappings;
1215         object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
1216         vp = object->handle;
1217         if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
1218                 ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
1219                 VOP_ADD_WRITECOUNT(vp, 1);
1220                 CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
1221                     __func__, vp, vp->v_writecount);
1222         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
1223                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
1224                 VOP_ADD_WRITECOUNT(vp, -1);
1225                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
1226                     __func__, vp, vp->v_writecount);
1227         }
1228         VM_OBJECT_WUNLOCK(object);
1229 }
1230
1231 void
1232 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
1233     vm_offset_t end)
1234 {
1235         struct vnode *vp;
1236         struct mount *mp;
1237         vm_offset_t inc;
1238
1239         VM_OBJECT_WLOCK(object);
1240
1241         /*
1242          * First, recheck the object type to account for the race when
1243          * the vnode is reclaimed.
1244          */
1245         if (object->type != OBJT_VNODE) {
1246                 VM_OBJECT_WUNLOCK(object);
1247                 return;
1248         }
1249
1250         /*
1251          * Optimize for the case when writemappings is not going to
1252          * zero.
1253          */
1254         inc = end - start;
1255         if (object->un_pager.vnp.writemappings != inc) {
1256                 object->un_pager.vnp.writemappings -= inc;
1257                 VM_OBJECT_WUNLOCK(object);
1258                 return;
1259         }
1260
1261         vp = object->handle;
1262         vhold(vp);
1263         VM_OBJECT_WUNLOCK(object);
1264         mp = NULL;
1265         vn_start_write(vp, &mp, V_WAIT);
1266         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
1267
1268         /*
1269          * Decrement the object's writemappings, by swapping the start
1270          * and end arguments for vnode_pager_update_writecount().  If
1271          * there was not a race with vnode reclaimation, then the
1272          * vnode's v_writecount is decremented.
1273          */
1274         vnode_pager_update_writecount(object, end, start);
1275         VOP_UNLOCK(vp, 0);
1276         vdrop(vp);
1277         if (mp != NULL)
1278                 vn_finished_write(mp);
1279 }