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                  * vclean() may be called twice. The first time
 162                  * removes the primary reference to the object,
 163                  * the second time goes one further and is a
 164                  * special-case to terminate the object.
 165                  *
 166                  * don't double-terminate the object
 167                  */
 168                 if ((obj->flags & OBJ_DEAD) == 0)
 169                         vm_object_terminate(obj);
 170                 else
 171                         VM_OBJECT_WUNLOCK(obj);
 172         } else {
 173                 /*
 174                  * Woe to the process that tries to page now :-).
 175                  */
 176                 vm_pager_deallocate(obj);
 177                 VM_OBJECT_WUNLOCK(obj);
 178         }
 179         vp->v_object = NULL;
 180 }
 181
 182
 183 /*
 184  * Allocate (or lookup) pager for a vnode.
 185  * Handle is a vnode pointer.
 186  *
 187  * MPSAFE
 188  */
 189 vm_object_t
 190 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 191     vm_ooffset_t offset, struct ucred *cred)
 192 {
 193         vm_object_t object;
 194         struct vnode *vp;
 195
 196         /*
 197          * Pageout to vnode, no can do yet.
 198          */
 199         if (handle == NULL)
 200                 return (NULL);
 201
 202         vp = (struct vnode *) handle;
 203
 204         /*
 205          * If the object is being terminated, wait for it to
 206          * go away.
 207          */
 208 retry:
 209         while ((object = vp->v_object) != NULL) {
 210                 VM_OBJECT_WLOCK(object);
 211                 if ((object->flags & OBJ_DEAD) == 0)
 212                         break;
 213                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 214                 VM_OBJECT_SLEEP(object, object, PDROP | PVM, "vadead", 0);
 215         }
 216
 217         KASSERT(vp->v_usecount != 0, ("vnode_pager_alloc: no vnode reference"));
 218
 219         if (object == NULL) {
 220                 /*
 221                  * Add an object of the appropriate size
 222                  */
 223                 object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
 224
 225                 object->un_pager.vnp.vnp_size = size;
 226                 object->un_pager.vnp.writemappings = 0;
 227
 228                 object->handle = handle;
 229                 VI_LOCK(vp);
 230                 if (vp->v_object != NULL) {
 231                         /*
 232                          * Object has been created while we were sleeping
 233                          */
 234                         VI_UNLOCK(vp);
 235                         vm_object_destroy(object);
 236                         goto retry;
 237                 }
 238                 vp->v_object = object;
 239                 VI_UNLOCK(vp);
 240         } else {
 241                 object->ref_count++;
 242                 VM_OBJECT_WUNLOCK(object);
 243         }
 244         vref(vp);
 245         return (object);
 246 }
 247
 248 /*
 249  *      The object must be locked.
 250  */
 251 static void
 252 vnode_pager_dealloc(object)
 253         vm_object_t object;
 254 {
 255         struct vnode *vp;
 256         int refs;
 257
 258         vp = object->handle;
 259         if (vp == NULL)
 260                 panic("vnode_pager_dealloc: pager already dealloced");
 261
 262         VM_OBJECT_ASSERT_WLOCKED(object);
 263         vm_object_pip_wait(object, "vnpdea");
 264         refs = object->ref_count;
 265
 266         object->handle = NULL;
 267         object->type = OBJT_DEAD;
 268         if (object->flags & OBJ_DISCONNECTWNT) {
 269                 vm_object_clear_flag(object, OBJ_DISCONNECTWNT);
 270                 wakeup(object);
 271         }
 272         ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
 273         if (object->un_pager.vnp.writemappings > 0) {
 274                 object->un_pager.vnp.writemappings = 0;
 275                 VOP_ADD_WRITECOUNT(vp, -1);
 276                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
 277                     __func__, vp, vp->v_writecount);
 278         }
 279         vp->v_object = NULL;
 280         VOP_UNSET_TEXT(vp);
 281         VM_OBJECT_WUNLOCK(object);
 282         while (refs-- > 0)
 283                 vunref(vp);
 284         VM_OBJECT_WLOCK(object);
 285 }
 286
 287 static boolean_t
 288 vnode_pager_haspage(object, pindex, before, after)
 289         vm_object_t object;
 290         vm_pindex_t pindex;
 291         int *before;
 292         int *after;
 293 {
 294         struct vnode *vp = object->handle;
 295         daddr_t bn;
 296         int err;
 297         daddr_t reqblock;
 298         int poff;
 299         int bsize;
 300         int pagesperblock, blocksperpage;
 301
 302         VM_OBJECT_ASSERT_WLOCKED(object);
 303         /*
 304          * If no vp or vp is doomed or marked transparent to VM, we do not
 305          * have the page.
 306          */
 307         if (vp == NULL || vp->v_iflag & VI_DOOMED)
 308                 return FALSE;
 309         /*
 310          * If the offset is beyond end of file we do
 311          * not have the page.
 312          */
 313         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
 314                 return FALSE;
 315
 316         bsize = vp->v_mount->mnt_stat.f_iosize;
 317         pagesperblock = bsize / PAGE_SIZE;
 318         blocksperpage = 0;
 319         if (pagesperblock > 0) {
 320                 reqblock = pindex / pagesperblock;
 321         } else {
 322                 blocksperpage = (PAGE_SIZE / bsize);
 323                 reqblock = pindex * blocksperpage;
 324         }
 325         VM_OBJECT_WUNLOCK(object);
 326         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
 327         VM_OBJECT_WLOCK(object);
 328         if (err)
 329                 return TRUE;
 330         if (bn == -1)
 331                 return FALSE;
 332         if (pagesperblock > 0) {
 333                 poff = pindex - (reqblock * pagesperblock);
 334                 if (before) {
 335                         *before *= pagesperblock;
 336                         *before += poff;
 337                 }
 338                 if (after) {
 339                         int numafter;
 340                         *after *= pagesperblock;
 341                         numafter = pagesperblock - (poff + 1);
 342                         if (IDX_TO_OFF(pindex + numafter) >
 343                             object->un_pager.vnp.vnp_size) {
 344                                 numafter =
 345                                     OFF_TO_IDX(object->un_pager.vnp.vnp_size) -
 346                                     pindex;
 347                         }
 348                         *after += numafter;
 349                 }
 350         } else {
 351                 if (before) {
 352                         *before /= blocksperpage;
 353                 }
 354
 355                 if (after) {
 356                         *after /= blocksperpage;
 357                 }
 358         }
 359         return TRUE;
 360 }
 361
 362 /*
 363  * Lets the VM system know about a change in size for a file.
 364  * We adjust our own internal size and flush any cached pages in
 365  * the associated object that are affected by the size change.
 366  *
 367  * Note: this routine may be invoked as a result of a pager put
 368  * operation (possibly at object termination time), so we must be careful.
 369  */
 370 void
 371 vnode_pager_setsize(vp, nsize)
 372         struct vnode *vp;
 373         vm_ooffset_t nsize;
 374 {
 375         vm_object_t object;
 376         vm_page_t m;
 377         vm_pindex_t nobjsize;
 378
 379         if ((object = vp->v_object) == NULL)
 380                 return;
 381 /*      ASSERT_VOP_ELOCKED(vp, "vnode_pager_setsize and not locked vnode"); */
 382         VM_OBJECT_WLOCK(object);
 383         if (object->type == OBJT_DEAD) {
 384                 VM_OBJECT_WUNLOCK(object);
 385                 return;
 386         }
 387         KASSERT(object->type == OBJT_VNODE,
 388             ("not vnode-backed object %p", object));
 389         if (nsize == object->un_pager.vnp.vnp_size) {
 390                 /*
 391                  * Hasn't changed size
 392                  */
 393                 VM_OBJECT_WUNLOCK(object);
 394                 return;
 395         }
 396         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
 397         if (nsize < object->un_pager.vnp.vnp_size) {
 398                 /*
 399                  * File has shrunk. Toss any cached pages beyond the new EOF.
 400                  */
 401                 if (nobjsize < object->size)
 402                         vm_object_page_remove(object, nobjsize, object->size,
 403                             0);
 404                 /*
 405                  * this gets rid of garbage at the end of a page that is now
 406                  * only partially backed by the vnode.
 407                  *
 408                  * XXX for some reason (I don't know yet), if we take a
 409                  * completely invalid page and mark it partially valid
 410                  * it can screw up NFS reads, so we don't allow the case.
 411                  */
 412                 if ((nsize & PAGE_MASK) &&
 413                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
 414                     m->valid != 0) {
 415                         int base = (int)nsize & PAGE_MASK;
 416                         int size = PAGE_SIZE - base;
 417
 418                         /*
 419                          * Clear out partial-page garbage in case
 420                          * the page has been mapped.
 421                          */
 422                         pmap_zero_page_area(m, base, size);
 423
 424                         /*
 425                          * Update the valid bits to reflect the blocks that
 426                          * have been zeroed.  Some of these valid bits may
 427                          * have already been set.
 428                          */
 429                         vm_page_set_valid_range(m, base, size);
 430
 431                         /*
 432                          * Round "base" to the next block boundary so that the
 433                          * dirty bit for a partially zeroed block is not
 434                          * cleared.
 435                          */
 436                         base = roundup2(base, DEV_BSIZE);
 437
 438                         /*
 439                          * Clear out partial-page dirty bits.
 440                          *
 441                          * note that we do not clear out the valid
 442                          * bits.  This would prevent bogus_page
 443                          * replacement from working properly.
 444                          */
 445                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
 446                 } else if ((nsize & PAGE_MASK) &&
 447                     vm_page_is_cached(object, OFF_TO_IDX(nsize))) {
 448                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
 449                             nobjsize);
 450                 }
 451         }
 452         object->un_pager.vnp.vnp_size = nsize;
 453         object->size = nobjsize;
 454         VM_OBJECT_WUNLOCK(object);
 455 }
 456
 457 /*
 458  * calculate the linear (byte) disk address of specified virtual
 459  * file address
 460  */
 461 static int
 462 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
 463     int *run)
 464 {
 465         int bsize;
 466         int err;
 467         daddr_t vblock;
 468         daddr_t voffset;
 469
 470         if (address < 0)
 471                 return -1;
 472
 473         if (vp->v_iflag & VI_DOOMED)
 474                 return -1;
 475
 476         bsize = vp->v_mount->mnt_stat.f_iosize;
 477         vblock = address / bsize;
 478         voffset = address % bsize;
 479
 480         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
 481         if (err == 0) {
 482                 if (*rtaddress != -1)
 483                         *rtaddress += voffset / DEV_BSIZE;
 484                 if (run) {
 485                         *run += 1;
 486                         *run *= bsize/PAGE_SIZE;
 487                         *run -= voffset/PAGE_SIZE;
 488                 }
 489         }
 490
 491         return (err);
 492 }
 493
 494 /*
 495  * small block filesystem vnode pager input
 496  */
 497 static int
 498 vnode_pager_input_smlfs(object, m)
 499         vm_object_t object;
 500         vm_page_t m;
 501 {
 502         struct vnode *vp;
 503         struct bufobj *bo;
 504         struct buf *bp;
 505         struct sf_buf *sf;
 506         daddr_t fileaddr;
 507         vm_offset_t bsize;
 508         vm_page_bits_t bits;
 509         int error, i;
 510
 511         error = 0;
 512         vp = object->handle;
 513         if (vp->v_iflag & VI_DOOMED)
 514                 return VM_PAGER_BAD;
 515
 516         bsize = vp->v_mount->mnt_stat.f_iosize;
 517
 518         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
 519
 520         sf = sf_buf_alloc(m, 0);
 521
 522         for (i = 0; i < PAGE_SIZE / bsize; i++) {
 523                 vm_ooffset_t address;
 524
 525                 bits = vm_page_bits(i * bsize, bsize);
 526                 if (m->valid & bits)
 527                         continue;
 528
 529                 address = IDX_TO_OFF(m->pindex) + i * bsize;
 530                 if (address >= object->un_pager.vnp.vnp_size) {
 531                         fileaddr = -1;
 532                 } else {
 533                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
 534                         if (error)
 535                                 break;
 536                 }
 537                 if (fileaddr != -1) {
 538                         bp = getpbuf(&vnode_pbuf_freecnt);
 539
 540                         /* build a minimal buffer header */
 541                         bp->b_iocmd = BIO_READ;
 542                         bp->b_iodone = bdone;
 543                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 544                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 545                         bp->b_rcred = crhold(curthread->td_ucred);
 546                         bp->b_wcred = crhold(curthread->td_ucred);
 547                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
 548                         bp->b_blkno = fileaddr;
 549                         pbgetbo(bo, bp);
 550                         bp->b_vp = vp;
 551                         bp->b_bcount = bsize;
 552                         bp->b_bufsize = bsize;
 553                         bp->b_runningbufspace = bp->b_bufsize;
 554                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 555
 556                         /* do the input */
 557                         bp->b_iooffset = dbtob(bp->b_blkno);
 558                         bstrategy(bp);
 559
 560                         bwait(bp, PVM, "vnsrd");
 561
 562                         if ((bp->b_ioflags & BIO_ERROR) != 0)
 563                                 error = EIO;
 564
 565                         /*
 566                          * free the buffer header back to the swap buffer pool
 567                          */
 568                         bp->b_vp = NULL;
 569                         pbrelbo(bp);
 570                         relpbuf(bp, &vnode_pbuf_freecnt);
 571                         if (error)
 572                                 break;
 573                 } else
 574                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
 575                 KASSERT((m->dirty & bits) == 0,
 576                     ("vnode_pager_input_smlfs: page %p is dirty", m));
 577                 VM_OBJECT_WLOCK(object);
 578                 m->valid |= bits;
 579                 VM_OBJECT_WUNLOCK(object);
 580         }
 581         sf_buf_free(sf);
 582         if (error) {
 583                 return VM_PAGER_ERROR;
 584         }
 585         return VM_PAGER_OK;
 586 }
 587
 588 /*
 589  * old style vnode pager input routine
 590  */
 591 static int
 592 vnode_pager_input_old(object, m)
 593         vm_object_t object;
 594         vm_page_t m;
 595 {
 596         struct uio auio;
 597         struct iovec aiov;
 598         int error;
 599         int size;
 600         struct sf_buf *sf;
 601         struct vnode *vp;
 602
 603         VM_OBJECT_ASSERT_WLOCKED(object);
 604         error = 0;
 605
 606         /*
 607          * Return failure if beyond current EOF
 608          */
 609         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
 610                 return VM_PAGER_BAD;
 611         } else {
 612                 size = PAGE_SIZE;
 613                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
 614                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
 615                 vp = object->handle;
 616                 VM_OBJECT_WUNLOCK(object);
 617
 618                 /*
 619                  * Allocate a kernel virtual address and initialize so that
 620                  * we can use VOP_READ/WRITE routines.
 621                  */
 622                 sf = sf_buf_alloc(m, 0);
 623
 624                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
 625                 aiov.iov_len = size;
 626                 auio.uio_iov = &aiov;
 627                 auio.uio_iovcnt = 1;
 628                 auio.uio_offset = IDX_TO_OFF(m->pindex);
 629                 auio.uio_segflg = UIO_SYSSPACE;
 630                 auio.uio_rw = UIO_READ;
 631                 auio.uio_resid = size;
 632                 auio.uio_td = curthread;
 633
 634                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
 635                 if (!error) {
 636                         int count = size - auio.uio_resid;
 637
 638                         if (count == 0)
 639                                 error = EINVAL;
 640                         else if (count != PAGE_SIZE)
 641                                 bzero((caddr_t)sf_buf_kva(sf) + count,
 642                                     PAGE_SIZE - count);
 643                 }
 644                 sf_buf_free(sf);
 645
 646                 VM_OBJECT_WLOCK(object);
 647         }
 648         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
 649         if (!error)
 650                 m->valid = VM_PAGE_BITS_ALL;
 651         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
 652 }
 653
 654 /*
 655  * generic vnode pager input routine
 656  */
 657
 658 /*
 659  * Local media VFS's that do not implement their own VOP_GETPAGES
 660  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 661  * to implement the previous behaviour.
 662  *
 663  * All other FS's should use the bypass to get to the local media
 664  * backing vp's VOP_GETPAGES.
 665  */
 666 static int
 667 vnode_pager_getpages(object, m, count, reqpage)
 668         vm_object_t object;
 669         vm_page_t *m;
 670         int count;
 671         int reqpage;
 672 {
 673         int rtval;
 674         struct vnode *vp;
 675         int bytes = count * PAGE_SIZE;
 676
 677         vp = object->handle;
 678         VM_OBJECT_WUNLOCK(object);
 679         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
 680         KASSERT(rtval != EOPNOTSUPP,
 681             ("vnode_pager: FS getpages not implemented\n"));
 682         VM_OBJECT_WLOCK(object);
 683         return rtval;
 684 }
 685
 686 /*
 687  * This is now called from local media FS's to operate against their
 688  * own vnodes if they fail to implement VOP_GETPAGES.
 689  */
 690 int
 691 vnode_pager_generic_getpages(vp, m, bytecount, reqpage)
 692         struct vnode *vp;
 693         vm_page_t *m;
 694         int bytecount;
 695         int reqpage;
 696 {
 697         vm_object_t object;
 698         vm_offset_t kva;
 699         off_t foff, tfoff, nextoff;
 700         int i, j, size, bsize, first;
 701         daddr_t firstaddr, reqblock;
 702         struct bufobj *bo;
 703         int runpg;
 704         int runend;
 705         struct buf *bp;
 706         struct mount *mp;
 707         int count;
 708         int error;
 709
 710         object = vp->v_object;
 711         count = bytecount / PAGE_SIZE;
 712
 713         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
 714             ("vnode_pager_generic_getpages does not support devices"));
 715         if (vp->v_iflag & VI_DOOMED)
 716                 return VM_PAGER_BAD;
 717
 718         bsize = vp->v_mount->mnt_stat.f_iosize;
 719
 720         /* get the UNDERLYING device for the file with VOP_BMAP() */
 721
 722         /*
 723          * originally, we did not check for an error return value -- assuming
 724          * an fs always has a bmap entry point -- that assumption is wrong!!!
 725          */
 726         foff = IDX_TO_OFF(m[reqpage]->pindex);
 727
 728         /*
 729          * if we can't bmap, use old VOP code
 730          */
 731         error = VOP_BMAP(vp, foff / bsize, &bo, &reqblock, NULL, NULL);
 732         if (error == EOPNOTSUPP) {
 733                 VM_OBJECT_WLOCK(object);
 734
 735                 for (i = 0; i < count; i++)
 736                         if (i != reqpage) {
 737                                 vm_page_lock(m[i]);
 738                                 vm_page_free(m[i]);
 739                                 vm_page_unlock(m[i]);
 740                         }
 741                 PCPU_INC(cnt.v_vnodein);
 742                 PCPU_INC(cnt.v_vnodepgsin);
 743                 error = vnode_pager_input_old(object, m[reqpage]);
 744                 VM_OBJECT_WUNLOCK(object);
 745                 return (error);
 746         } else if (error != 0) {
 747                 VM_OBJECT_WLOCK(object);
 748                 for (i = 0; i < count; i++)
 749                         if (i != reqpage) {
 750                                 vm_page_lock(m[i]);
 751                                 vm_page_free(m[i]);
 752                                 vm_page_unlock(m[i]);
 753                         }
 754                 VM_OBJECT_WUNLOCK(object);
 755                 return (VM_PAGER_ERROR);
 756
 757                 /*
 758                  * if the blocksize is smaller than a page size, then use
 759                  * special small filesystem code.  NFS sometimes has a small
 760                  * blocksize, but it can handle large reads itself.
 761                  */
 762         } else if ((PAGE_SIZE / bsize) > 1 &&
 763             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
 764                 VM_OBJECT_WLOCK(object);
 765                 for (i = 0; i < count; i++)
 766                         if (i != reqpage) {
 767                                 vm_page_lock(m[i]);
 768                                 vm_page_free(m[i]);
 769                                 vm_page_unlock(m[i]);
 770                         }
 771                 VM_OBJECT_WUNLOCK(object);
 772                 PCPU_INC(cnt.v_vnodein);
 773                 PCPU_INC(cnt.v_vnodepgsin);
 774                 return vnode_pager_input_smlfs(object, m[reqpage]);
 775         }
 776
 777         /*
 778          * If we have a completely valid page available to us, we can
 779          * clean up and return.  Otherwise we have to re-read the
 780          * media.
 781          */
 782         VM_OBJECT_WLOCK(object);
 783         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
 784                 for (i = 0; i < count; i++)
 785                         if (i != reqpage) {
 786                                 vm_page_lock(m[i]);
 787                                 vm_page_free(m[i]);
 788                                 vm_page_unlock(m[i]);
 789                         }
 790                 VM_OBJECT_WUNLOCK(object);
 791                 return VM_PAGER_OK;
 792         } else if (reqblock == -1) {
 793                 pmap_zero_page(m[reqpage]);
 794                 KASSERT(m[reqpage]->dirty == 0,
 795                     ("vnode_pager_generic_getpages: page %p is dirty", m));
 796                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
 797                 for (i = 0; i < count; i++)
 798                         if (i != reqpage) {
 799                                 vm_page_lock(m[i]);
 800                                 vm_page_free(m[i]);
 801                                 vm_page_unlock(m[i]);
 802                         }
 803                 VM_OBJECT_WUNLOCK(object);
 804                 return (VM_PAGER_OK);
 805         }
 806         m[reqpage]->valid = 0;
 807         VM_OBJECT_WUNLOCK(object);
 808
 809         /*
 810          * here on direct device I/O
 811          */
 812         firstaddr = -1;
 813
 814         /*
 815          * calculate the run that includes the required page
 816          */
 817         for (first = 0, i = 0; i < count; i = runend) {
 818                 if (vnode_pager_addr(vp, IDX_TO_OFF(m[i]->pindex), &firstaddr,
 819                     &runpg) != 0) {
 820                         VM_OBJECT_WLOCK(object);
 821                         for (; i < count; i++)
 822                                 if (i != reqpage) {
 823                                         vm_page_lock(m[i]);
 824                                         vm_page_free(m[i]);
 825                                         vm_page_unlock(m[i]);
 826                                 }
 827                         VM_OBJECT_WUNLOCK(object);
 828                         return (VM_PAGER_ERROR);
 829                 }
 830                 if (firstaddr == -1) {
 831                         VM_OBJECT_WLOCK(object);
 832                         if (i == reqpage && foff < object->un_pager.vnp.vnp_size) {
 833                                 panic("vnode_pager_getpages: unexpected missing page: firstaddr: %jd, foff: 0x%jx%08jx, vnp_size: 0x%jx%08jx",
 834                                     (intmax_t)firstaddr, (uintmax_t)(foff >> 32),
 835                                     (uintmax_t)foff,
 836                                     (uintmax_t)
 837                                     (object->un_pager.vnp.vnp_size >> 32),
 838                                     (uintmax_t)object->un_pager.vnp.vnp_size);
 839                         }
 840                         vm_page_lock(m[i]);
 841                         vm_page_free(m[i]);
 842                         vm_page_unlock(m[i]);
 843                         VM_OBJECT_WUNLOCK(object);
 844                         runend = i + 1;
 845                         first = runend;
 846                         continue;
 847                 }
 848                 runend = i + runpg;
 849                 if (runend <= reqpage) {
 850                         VM_OBJECT_WLOCK(object);
 851                         for (j = i; j < runend; j++) {
 852                                 vm_page_lock(m[j]);
 853                                 vm_page_free(m[j]);
 854                                 vm_page_unlock(m[j]);
 855                         }
 856                         VM_OBJECT_WUNLOCK(object);
 857                 } else {
 858                         if (runpg < (count - first)) {
 859                                 VM_OBJECT_WLOCK(object);
 860                                 for (i = first + runpg; i < count; i++) {
 861                                         vm_page_lock(m[i]);
 862                                         vm_page_free(m[i]);
 863                                         vm_page_unlock(m[i]);
 864                                 }
 865                                 VM_OBJECT_WUNLOCK(object);
 866                                 count = first + runpg;
 867                         }
 868                         break;
 869                 }
 870                 first = runend;
 871         }
 872
 873         /*
 874          * the first and last page have been calculated now, move input pages
 875          * to be zero based...
 876          */
 877         if (first != 0) {
 878                 m += first;
 879                 count -= first;
 880                 reqpage -= first;
 881         }
 882
 883         /*
 884          * calculate the file virtual address for the transfer
 885          */
 886         foff = IDX_TO_OFF(m[0]->pindex);
 887
 888         /*
 889          * calculate the size of the transfer
 890          */
 891         size = count * PAGE_SIZE;
 892         KASSERT(count > 0, ("zero count"));
 893         if ((foff + size) > object->un_pager.vnp.vnp_size)
 894                 size = object->un_pager.vnp.vnp_size - foff;
 895         KASSERT(size > 0, ("zero size"));
 896
 897         /*
 898          * round up physical size for real devices.
 899          */
 900         if (1) {
 901                 int secmask = bo->bo_bsize - 1;
 902                 KASSERT(secmask < PAGE_SIZE && secmask > 0,
 903                     ("vnode_pager_generic_getpages: sector size %d too large",
 904                     secmask + 1));
 905                 size = (size + secmask) & ~secmask;
 906         }
 907
 908         bp = getpbuf(&vnode_pbuf_freecnt);
 909         kva = (vm_offset_t)bp->b_data;
 910
 911         /*
 912          * and map the pages to be read into the kva, if the filesystem
 913          * requires mapped buffers.
 914          */
 915         mp = vp->v_mount;
 916         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0 &&
 917             unmapped_buf_allowed) {
 918                 bp->b_data = unmapped_buf;
 919                 bp->b_kvabase = unmapped_buf;
 920                 bp->b_offset = 0;
 921                 bp->b_flags |= B_UNMAPPED;
 922                 bp->b_npages = count;
 923                 for (i = 0; i < count; i++)
 924                         bp->b_pages[i] = m[i];
 925         } else
 926                 pmap_qenter(kva, m, count);
 927
 928         /* build a minimal buffer header */
 929         bp->b_iocmd = BIO_READ;
 930         bp->b_iodone = bdone;
 931         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 932         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 933         bp->b_rcred = crhold(curthread->td_ucred);
 934         bp->b_wcred = crhold(curthread->td_ucred);
 935         bp->b_blkno = firstaddr;
 936         pbgetbo(bo, bp);
 937         bp->b_vp = vp;
 938         bp->b_bcount = size;
 939         bp->b_bufsize = size;
 940         bp->b_runningbufspace = bp->b_bufsize;
 941         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 942
 943         PCPU_INC(cnt.v_vnodein);
 944         PCPU_ADD(cnt.v_vnodepgsin, count);
 945
 946         /* do the input */
 947         bp->b_iooffset = dbtob(bp->b_blkno);
 948         bstrategy(bp);
 949
 950         bwait(bp, PVM, "vnread");
 951
 952         if ((bp->b_ioflags & BIO_ERROR) != 0)
 953                 error = EIO;
 954
 955         if (error == 0 && size != count * PAGE_SIZE) {
 956                 if ((bp->b_flags & B_UNMAPPED) != 0) {
 957                         bp->b_flags &= ~B_UNMAPPED;
 958                         pmap_qenter(kva, m, count);
 959                 }
 960                 bzero((caddr_t)kva + size, PAGE_SIZE * count - size);
 961         }
 962         if ((bp->b_flags & B_UNMAPPED) == 0)
 963                 pmap_qremove(kva, count);
 964         if (mp != NULL && (mp->mnt_kern_flag & MNTK_UNMAPPED_BUFS) != 0) {
 965                 bp->b_data = (caddr_t)kva;
 966                 bp->b_kvabase = (caddr_t)kva;
 967                 bp->b_flags &= ~B_UNMAPPED;
 968                 for (i = 0; i < count; i++)
 969                         bp->b_pages[i] = NULL;
 970         }
 971
 972         /*
 973          * free the buffer header back to the swap buffer pool
 974          */
 975         bp->b_vp = NULL;
 976         pbrelbo(bp);
 977         relpbuf(bp, &vnode_pbuf_freecnt);
 978
 979         VM_OBJECT_WLOCK(object);
 980         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
 981                 vm_page_t mt;
 982
 983                 nextoff = tfoff + PAGE_SIZE;
 984                 mt = m[i];
 985
 986                 if (nextoff <= object->un_pager.vnp.vnp_size) {
 987                         /*
 988                          * Read filled up entire page.
 989                          */
 990                         mt->valid = VM_PAGE_BITS_ALL;
 991                         KASSERT(mt->dirty == 0,
 992                             ("vnode_pager_generic_getpages: page %p is dirty",
 993                             mt));
 994                         KASSERT(!pmap_page_is_mapped(mt),
 995                             ("vnode_pager_generic_getpages: page %p is mapped",
 996                             mt));
 997                 } else {
 998                         /*
 999                          * Read did not fill up entire page.
1000                          *
1001                          * Currently we do not set the entire page valid,
1002                          * we just try to clear the piece that we couldn't
1003                          * read.
1004                          */
1005                         vm_page_set_valid_range(mt, 0,
1006                             object->un_pager.vnp.vnp_size - tfoff);
1007                         KASSERT((mt->dirty & vm_page_bits(0,
1008                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
1009                             ("vnode_pager_generic_getpages: page %p is dirty",
1010                             mt));
1011                 }
1012
1013                 if (i != reqpage)
1014                         vm_page_readahead_finish(mt);
1015         }
1016         VM_OBJECT_WUNLOCK(object);
1017         if (error) {
1018                 printf("vnode_pager_getpages: I/O read error\n");
1019         }
1020         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
1021 }
1022
1023 /*
1024  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
1025  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
1026  * vnode_pager_generic_putpages() to implement the previous behaviour.
1027  *
1028  * All other FS's should use the bypass to get to the local media
1029  * backing vp's VOP_PUTPAGES.
1030  */
1031 static void
1032 vnode_pager_putpages(object, m, count, sync, rtvals)
1033         vm_object_t object;
1034         vm_page_t *m;
1035         int count;
1036         boolean_t sync;
1037         int *rtvals;
1038 {
1039         int rtval;
1040         struct vnode *vp;
1041         int bytes = count * PAGE_SIZE;
1042
1043         /*
1044          * Force synchronous operation if we are extremely low on memory
1045          * to prevent a low-memory deadlock.  VOP operations often need to
1046          * allocate more memory to initiate the I/O ( i.e. do a BMAP
1047          * operation ).  The swapper handles the case by limiting the amount
1048          * of asynchronous I/O, but that sort of solution doesn't scale well
1049          * for the vnode pager without a lot of work.
1050          *
1051          * Also, the backing vnode's iodone routine may not wake the pageout
1052          * daemon up.  This should be probably be addressed XXX.
1053          */
1054
1055         if ((cnt.v_free_count + cnt.v_cache_count) < cnt.v_pageout_free_min)
1056                 sync |= OBJPC_SYNC;
1057
1058         /*
1059          * Call device-specific putpages function
1060          */
1061         vp = object->handle;
1062         VM_OBJECT_WUNLOCK(object);
1063         rtval = VOP_PUTPAGES(vp, m, bytes, sync, rtvals, 0);
1064         KASSERT(rtval != EOPNOTSUPP,
1065             ("vnode_pager: stale FS putpages\n"));
1066         VM_OBJECT_WLOCK(object);
1067 }
1068
1069
1070 /*
1071  * This is now called from local media FS's to operate against their
1072  * own vnodes if they fail to implement VOP_PUTPAGES.
1073  *
1074  * This is typically called indirectly via the pageout daemon and
1075  * clustering has already typically occured, so in general we ask the
1076  * underlying filesystem to write the data out asynchronously rather
1077  * then delayed.
1078  */
1079 int
1080 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
1081     int flags, int *rtvals)
1082 {
1083         int i;
1084         vm_object_t object;
1085         vm_page_t m;
1086         int count;
1087
1088         int maxsize, ncount;
1089         vm_ooffset_t poffset;
1090         struct uio auio;
1091         struct iovec aiov;
1092         int error;
1093         int ioflags;
1094         int ppscheck = 0;
1095         static struct timeval lastfail;
1096         static int curfail;
1097
1098         object = vp->v_object;
1099         count = bytecount / PAGE_SIZE;
1100
1101         for (i = 0; i < count; i++)
1102                 rtvals[i] = VM_PAGER_ERROR;
1103
1104         if ((int64_t)ma[0]->pindex < 0) {
1105                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
1106                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
1107                 rtvals[0] = VM_PAGER_BAD;
1108                 return VM_PAGER_BAD;
1109         }
1110
1111         maxsize = count * PAGE_SIZE;
1112         ncount = count;
1113
1114         poffset = IDX_TO_OFF(ma[0]->pindex);
1115
1116         /*
1117          * If the page-aligned write is larger then the actual file we
1118          * have to invalidate pages occuring beyond the file EOF.  However,
1119          * there is an edge case where a file may not be page-aligned where
1120          * the last page is partially invalid.  In this case the filesystem
1121          * may not properly clear the dirty bits for the entire page (which
1122          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
1123          * With the page locked we are free to fix-up the dirty bits here.
1124          *
1125          * We do not under any circumstances truncate the valid bits, as
1126          * this will screw up bogus page replacement.
1127          */
1128         VM_OBJECT_WLOCK(object);
1129         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
1130                 if (object->un_pager.vnp.vnp_size > poffset) {
1131                         int pgoff;
1132
1133                         maxsize = object->un_pager.vnp.vnp_size - poffset;
1134                         ncount = btoc(maxsize);
1135                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
1136                                 /*
1137                                  * If the object is locked and the following
1138                                  * conditions hold, then the page's dirty
1139                                  * field cannot be concurrently changed by a
1140                                  * pmap operation.
1141                                  */
1142                                 m = ma[ncount - 1];
1143                                 KASSERT(m->busy > 0,
1144                 ("vnode_pager_generic_putpages: page %p is not busy", m));
1145                                 KASSERT(!pmap_page_is_write_mapped(m),
1146                 ("vnode_pager_generic_putpages: page %p is not read-only", m));
1147                                 vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
1148                                     pgoff);
1149                         }
1150                 } else {
1151                         maxsize = 0;
1152                         ncount = 0;
1153                 }
1154                 if (ncount < count) {
1155                         for (i = ncount; i < count; i++) {
1156                                 rtvals[i] = VM_PAGER_BAD;
1157                         }
1158                 }
1159         }
1160         VM_OBJECT_WUNLOCK(object);
1161
1162         /*
1163          * pageouts are already clustered, use IO_ASYNC to force a bawrite()
1164          * rather then a bdwrite() to prevent paging I/O from saturating
1165          * the buffer cache.  Dummy-up the sequential heuristic to cause
1166          * large ranges to cluster.  If neither IO_SYNC or IO_ASYNC is set,
1167          * the system decides how to cluster.
1168          */
1169         ioflags = IO_VMIO;
1170         if (flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL))
1171                 ioflags |= IO_SYNC;
1172         else if ((flags & VM_PAGER_CLUSTER_OK) == 0)
1173                 ioflags |= IO_ASYNC;
1174         ioflags |= (flags & VM_PAGER_PUT_INVAL) ? IO_INVAL: 0;
1175         ioflags |= IO_SEQMAX << IO_SEQSHIFT;
1176
1177         aiov.iov_base = (caddr_t) 0;
1178         aiov.iov_len = maxsize;
1179         auio.uio_iov = &aiov;
1180         auio.uio_iovcnt = 1;
1181         auio.uio_offset = poffset;
1182         auio.uio_segflg = UIO_NOCOPY;
1183         auio.uio_rw = UIO_WRITE;
1184         auio.uio_resid = maxsize;
1185         auio.uio_td = (struct thread *) 0;
1186         error = VOP_WRITE(vp, &auio, ioflags, curthread->td_ucred);
1187         PCPU_INC(cnt.v_vnodeout);
1188         PCPU_ADD(cnt.v_vnodepgsout, ncount);
1189
1190         if (error) {
1191                 if ((ppscheck = ppsratecheck(&lastfail, &curfail, 1)))
1192                         printf("vnode_pager_putpages: I/O error %d\n", error);
1193         }
1194         if (auio.uio_resid) {
1195                 if (ppscheck || ppsratecheck(&lastfail, &curfail, 1))
1196                         printf("vnode_pager_putpages: residual I/O %zd at %lu\n",
1197                             auio.uio_resid, (u_long)ma[0]->pindex);
1198         }
1199         for (i = 0; i < ncount; i++) {
1200                 rtvals[i] = VM_PAGER_OK;
1201         }
1202         return rtvals[0];
1203 }
1204
1205 void
1206 vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
1207 {
1208         vm_object_t obj;
1209         int i, pos;
1210
1211         if (written == 0)
1212                 return;
1213         obj = ma[0]->object;
1214         VM_OBJECT_WLOCK(obj);
1215         for (i = 0, pos = 0; pos < written; i++, pos += PAGE_SIZE) {
1216                 if (pos < trunc_page(written)) {
1217                         rtvals[i] = VM_PAGER_OK;
1218                         vm_page_undirty(ma[i]);
1219                 } else {
1220                         /* Partially written page. */
1221                         rtvals[i] = VM_PAGER_AGAIN;
1222                         vm_page_clear_dirty(ma[i], 0, written & PAGE_MASK);
1223                 }
1224         }
1225         VM_OBJECT_WUNLOCK(obj);
1226 }
1227
1228 void
1229 vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
1230     vm_offset_t end)
1231 {
1232         struct vnode *vp;
1233         vm_ooffset_t old_wm;
1234
1235         VM_OBJECT_WLOCK(object);
1236         if (object->type != OBJT_VNODE) {
1237                 VM_OBJECT_WUNLOCK(object);
1238                 return;
1239         }
1240         old_wm = object->un_pager.vnp.writemappings;
1241         object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
1242         vp = object->handle;
1243         if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
1244                 ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
1245                 VOP_ADD_WRITECOUNT(vp, 1);
1246                 CTR3(KTR_VFS, "%s: vp %p v_writecount increased to %d",
1247                     __func__, vp, vp->v_writecount);
1248         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
1249                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
1250                 VOP_ADD_WRITECOUNT(vp, -1);
1251                 CTR3(KTR_VFS, "%s: vp %p v_writecount decreased to %d",
1252                     __func__, vp, vp->v_writecount);
1253         }
1254         VM_OBJECT_WUNLOCK(object);
1255 }
1256
1257 void
1258 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
1259     vm_offset_t end)
1260 {
1261         struct vnode *vp;
1262         struct mount *mp;
1263         vm_offset_t inc;
1264
1265         VM_OBJECT_WLOCK(object);
1266
1267         /*
1268          * First, recheck the object type to account for the race when
1269          * the vnode is reclaimed.
1270          */
1271         if (object->type != OBJT_VNODE) {
1272                 VM_OBJECT_WUNLOCK(object);
1273                 return;
1274         }
1275
1276         /*
1277          * Optimize for the case when writemappings is not going to
1278          * zero.
1279          */
1280         inc = end - start;
1281         if (object->un_pager.vnp.writemappings != inc) {
1282                 object->un_pager.vnp.writemappings -= inc;
1283                 VM_OBJECT_WUNLOCK(object);
1284                 return;
1285         }
1286
1287         vp = object->handle;
1288         vhold(vp);
1289         VM_OBJECT_WUNLOCK(object);
1290         mp = NULL;
1291         vn_start_write(vp, &mp, V_WAIT);
1292         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
1293
1294         /*
1295          * Decrement the object's writemappings, by swapping the start
1296          * and end arguments for vnode_pager_update_writecount().  If
1297          * there was not a race with vnode reclaimation, then the
1298          * vnode's v_writecount is decremented.
1299          */
1300         vnode_pager_update_writecount(object, end, start);
1301         VOP_UNLOCK(vp, 0);
1302         vdrop(vp);
1303         if (mp != NULL)
1304                 vn_finished_write(mp);
1305 }