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/sf_buf.h>
  67
  68 #include <machine/atomic.h>
  69
  70 #include <vm/vm.h>
  71 #include <vm/vm_param.h>
  72 #include <vm/vm_object.h>
  73 #include <vm/vm_page.h>
  74 #include <vm/vm_pager.h>
  75 #include <vm/vm_map.h>
  76 #include <vm/vnode_pager.h>
  77 #include <vm/vm_extern.h>
  78
  79 static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
  80     daddr_t *rtaddress, int *run);
  81 static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
  82 static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
  83 static void vnode_pager_dealloc(vm_object_t);
  84 static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int);
  85 static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
  86 static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
  87 static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
  88     vm_ooffset_t, struct ucred *cred);
  89
  90 struct pagerops vnodepagerops = {
  91         .pgo_alloc =    vnode_pager_alloc,
  92         .pgo_dealloc =  vnode_pager_dealloc,
  93         .pgo_getpages = vnode_pager_getpages,
  94         .pgo_putpages = vnode_pager_putpages,
  95         .pgo_haspage =  vnode_pager_haspage,
  96 };
  97
  98 int vnode_pbuf_freecnt;
  99
 100 /* Create the VM system backing object for this vnode */
 101 int
 102 vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
 103 {
 104         vm_object_t object;
 105         vm_ooffset_t size = isize;
 106         struct vattr va;
 107
 108         if (!vn_isdisk(vp, NULL) && vn_canvmio(vp) == FALSE)
 109                 return (0);
 110
 111         while ((object = vp->v_object) != NULL) {
 112                 VM_OBJECT_LOCK(object);
 113                 if (!(object->flags & OBJ_DEAD)) {
 114                         VM_OBJECT_UNLOCK(object);
 115                         return (0);
 116                 }
 117                 VOP_UNLOCK(vp, 0);
 118                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 119                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vodead", 0);
 120                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 121         }
 122
 123         if (size == 0) {
 124                 if (vn_isdisk(vp, NULL)) {
 125                         size = IDX_TO_OFF(INT_MAX);
 126                 } else {
 127                         if (VOP_GETATTR(vp, &va, td->td_ucred))
 128                                 return (0);
 129                         size = va.va_size;
 130                 }
 131         }
 132
 133         object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
 134         /*
 135          * Dereference the reference we just created.  This assumes
 136          * that the object is associated with the vp.
 137          */
 138         VM_OBJECT_LOCK(object);
 139         object->ref_count--;
 140         VM_OBJECT_UNLOCK(object);
 141         vrele(vp);
 142
 143         KASSERT(vp->v_object != NULL, ("vnode_create_vobject: NULL object"));
 144
 145         return (0);
 146 }
 147
 148 void
 149 vnode_destroy_vobject(struct vnode *vp)
 150 {
 151         struct vm_object *obj;
 152
 153         obj = vp->v_object;
 154         if (obj == NULL)
 155                 return;
 156         ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
 157         VM_OBJECT_LOCK(obj);
 158         if (obj->ref_count == 0) {
 159                 /*
 160                  * vclean() may be called twice. The first time
 161                  * removes the primary reference to the object,
 162                  * the second time goes one further and is a
 163                  * special-case to terminate the object.
 164                  *
 165                  * don't double-terminate the object
 166                  */
 167                 if ((obj->flags & OBJ_DEAD) == 0)
 168                         vm_object_terminate(obj);
 169                 else
 170                         VM_OBJECT_UNLOCK(obj);
 171         } else {
 172                 /*
 173                  * Woe to the process that tries to page now :-).
 174                  */
 175                 vm_pager_deallocate(obj);
 176                 VM_OBJECT_UNLOCK(obj);
 177         }
 178         vp->v_object = NULL;
 179 }
 180
 181
 182 /*
 183  * Allocate (or lookup) pager for a vnode.
 184  * Handle is a vnode pointer.
 185  *
 186  * MPSAFE
 187  */
 188 vm_object_t
 189 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 190     vm_ooffset_t offset, struct ucred *cred)
 191 {
 192         vm_object_t object;
 193         struct vnode *vp;
 194
 195         /*
 196          * Pageout to vnode, no can do yet.
 197          */
 198         if (handle == NULL)
 199                 return (NULL);
 200
 201         vp = (struct vnode *) handle;
 202
 203         /*
 204          * If the object is being terminated, wait for it to
 205          * go away.
 206          */
 207 retry:
 208         while ((object = vp->v_object) != NULL) {
 209                 VM_OBJECT_LOCK(object);
 210                 if ((object->flags & OBJ_DEAD) == 0)
 211                         break;
 212                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 213                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vadead", 0);
 214         }
 215
 216         if (vp->v_usecount == 0)
 217                 panic("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_UNLOCK(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_LOCK_ASSERT(object, MA_OWNED);
 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         }
 277         vp->v_object = NULL;
 278         VOP_UNSET_TEXT(vp);
 279         VM_OBJECT_UNLOCK(object);
 280         while (refs-- > 0)
 281                 vunref(vp);
 282         VM_OBJECT_LOCK(object);
 283 }
 284
 285 static boolean_t
 286 vnode_pager_haspage(object, pindex, before, after)
 287         vm_object_t object;
 288         vm_pindex_t pindex;
 289         int *before;
 290         int *after;
 291 {
 292         struct vnode *vp = object->handle;
 293         daddr_t bn;
 294         int err;
 295         daddr_t reqblock;
 296         int poff;
 297         int bsize;
 298         int pagesperblock, blocksperpage;
 299         int vfslocked;
 300
 301         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 302         /*
 303          * If no vp or vp is doomed or marked transparent to VM, we do not
 304          * have the page.
 305          */
 306         if (vp == NULL || vp->v_iflag & VI_DOOMED)
 307                 return FALSE;
 308         /*
 309          * If the offset is beyond end of file we do
 310          * not have the page.
 311          */
 312         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
 313                 return FALSE;
 314
 315         bsize = vp->v_mount->mnt_stat.f_iosize;
 316         pagesperblock = bsize / PAGE_SIZE;
 317         blocksperpage = 0;
 318         if (pagesperblock > 0) {
 319                 reqblock = pindex / pagesperblock;
 320         } else {
 321                 blocksperpage = (PAGE_SIZE / bsize);
 322                 reqblock = pindex * blocksperpage;
 323         }
 324         VM_OBJECT_UNLOCK(object);
 325         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 326         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
 327         VFS_UNLOCK_GIANT(vfslocked);
 328         VM_OBJECT_LOCK(object);
 329         if (err)
 330                 return TRUE;
 331         if (bn == -1)
 332                 return FALSE;
 333         if (pagesperblock > 0) {
 334                 poff = pindex - (reqblock * pagesperblock);
 335                 if (before) {
 336                         *before *= pagesperblock;
 337                         *before += poff;
 338                 }
 339                 if (after) {
 340                         int numafter;
 341                         *after *= pagesperblock;
 342                         numafter = pagesperblock - (poff + 1);
 343                         if (IDX_TO_OFF(pindex + numafter) >
 344                             object->un_pager.vnp.vnp_size) {
 345                                 numafter =
 346                                     OFF_TO_IDX(object->un_pager.vnp.vnp_size) -
 347                                     pindex;
 348                         }
 349                         *after += numafter;
 350                 }
 351         } else {
 352                 if (before) {
 353                         *before /= blocksperpage;
 354                 }
 355
 356                 if (after) {
 357                         *after /= blocksperpage;
 358                 }
 359         }
 360         return TRUE;
 361 }
 362
 363 /*
 364  * Lets the VM system know about a change in size for a file.
 365  * We adjust our own internal size and flush any cached pages in
 366  * the associated object that are affected by the size change.
 367  *
 368  * Note: this routine may be invoked as a result of a pager put
 369  * operation (possibly at object termination time), so we must be careful.
 370  */
 371 void
 372 vnode_pager_setsize(vp, nsize)
 373         struct vnode *vp;
 374         vm_ooffset_t nsize;
 375 {
 376         vm_object_t object;
 377         vm_page_t m;
 378         vm_pindex_t nobjsize;
 379
 380         if ((object = vp->v_object) == NULL)
 381                 return;
 382 /*      ASSERT_VOP_ELOCKED(vp, "vnode_pager_setsize and not locked vnode"); */
 383         VM_OBJECT_LOCK(object);
 384         if (nsize == object->un_pager.vnp.vnp_size) {
 385                 /*
 386                  * Hasn't changed size
 387                  */
 388                 VM_OBJECT_UNLOCK(object);
 389                 return;
 390         }
 391         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
 392         if (nsize < object->un_pager.vnp.vnp_size) {
 393                 /*
 394                  * File has shrunk. Toss any cached pages beyond the new EOF.
 395                  */
 396                 if (nobjsize < object->size)
 397                         vm_object_page_remove(object, nobjsize, object->size,
 398                             0);
 399                 /*
 400                  * this gets rid of garbage at the end of a page that is now
 401                  * only partially backed by the vnode.
 402                  *
 403                  * XXX for some reason (I don't know yet), if we take a
 404                  * completely invalid page and mark it partially valid
 405                  * it can screw up NFS reads, so we don't allow the case.
 406                  */
 407                 if ((nsize & PAGE_MASK) &&
 408                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
 409                     m->valid != 0) {
 410                         int base = (int)nsize & PAGE_MASK;
 411                         int size = PAGE_SIZE - base;
 412
 413                         /*
 414                          * Clear out partial-page garbage in case
 415                          * the page has been mapped.
 416                          */
 417                         pmap_zero_page_area(m, base, size);
 418
 419                         /*
 420                          * Update the valid bits to reflect the blocks that
 421                          * have been zeroed.  Some of these valid bits may
 422                          * have already been set.
 423                          */
 424                         vm_page_set_valid(m, base, size);
 425
 426                         /*
 427                          * Round "base" to the next block boundary so that the
 428                          * dirty bit for a partially zeroed block is not
 429                          * cleared.
 430                          */
 431                         base = roundup2(base, DEV_BSIZE);
 432
 433                         /*
 434                          * Clear out partial-page dirty bits.
 435                          *
 436                          * note that we do not clear out the valid
 437                          * bits.  This would prevent bogus_page
 438                          * replacement from working properly.
 439                          */
 440                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
 441                 } else if ((nsize & PAGE_MASK) &&
 442                     __predict_false(object->cache != NULL)) {
 443                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
 444                             nobjsize);
 445                 }
 446         }
 447         object->un_pager.vnp.vnp_size = nsize;
 448         object->size = nobjsize;
 449         VM_OBJECT_UNLOCK(object);
 450 }
 451
 452 /*
 453  * calculate the linear (byte) disk address of specified virtual
 454  * file address
 455  */
 456 static int
 457 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
 458     int *run)
 459 {
 460         int bsize;
 461         int err;
 462         daddr_t vblock;
 463         daddr_t voffset;
 464
 465         if (address < 0)
 466                 return -1;
 467
 468         if (vp->v_iflag & VI_DOOMED)
 469                 return -1;
 470
 471         bsize = vp->v_mount->mnt_stat.f_iosize;
 472         vblock = address / bsize;
 473         voffset = address % bsize;
 474
 475         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
 476         if (err == 0) {
 477                 if (*rtaddress != -1)
 478                         *rtaddress += voffset / DEV_BSIZE;
 479                 if (run) {
 480                         *run += 1;
 481                         *run *= bsize/PAGE_SIZE;
 482                         *run -= voffset/PAGE_SIZE;
 483                 }
 484         }
 485
 486         return (err);
 487 }
 488
 489 /*
 490  * small block filesystem vnode pager input
 491  */
 492 static int
 493 vnode_pager_input_smlfs(object, m)
 494         vm_object_t object;
 495         vm_page_t m;
 496 {
 497         struct vnode *vp;
 498         struct bufobj *bo;
 499         struct buf *bp;
 500         struct sf_buf *sf;
 501         daddr_t fileaddr;
 502         vm_offset_t bsize;
 503         vm_page_bits_t bits;
 504         int error, i;
 505
 506         error = 0;
 507         vp = object->handle;
 508         if (vp->v_iflag & VI_DOOMED)
 509                 return VM_PAGER_BAD;
 510
 511         bsize = vp->v_mount->mnt_stat.f_iosize;
 512
 513         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
 514
 515         sf = sf_buf_alloc(m, 0);
 516
 517         for (i = 0; i < PAGE_SIZE / bsize; i++) {
 518                 vm_ooffset_t address;
 519
 520                 bits = vm_page_bits(i * bsize, bsize);
 521                 if (m->valid & bits)
 522                         continue;
 523
 524                 address = IDX_TO_OFF(m->pindex) + i * bsize;
 525                 if (address >= object->un_pager.vnp.vnp_size) {
 526                         fileaddr = -1;
 527                 } else {
 528                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
 529                         if (error)
 530                                 break;
 531                 }
 532                 if (fileaddr != -1) {
 533                         bp = getpbuf(&vnode_pbuf_freecnt);
 534
 535                         /* build a minimal buffer header */
 536                         bp->b_iocmd = BIO_READ;
 537                         bp->b_iodone = bdone;
 538                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 539                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 540                         bp->b_rcred = crhold(curthread->td_ucred);
 541                         bp->b_wcred = crhold(curthread->td_ucred);
 542                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
 543                         bp->b_blkno = fileaddr;
 544                         pbgetbo(bo, bp);
 545                         bp->b_vp = vp;
 546                         bp->b_bcount = bsize;
 547                         bp->b_bufsize = bsize;
 548                         bp->b_runningbufspace = bp->b_bufsize;
 549                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 550
 551                         /* do the input */
 552                         bp->b_iooffset = dbtob(bp->b_blkno);
 553                         bstrategy(bp);
 554
 555                         bwait(bp, PVM, "vnsrd");
 556
 557                         if ((bp->b_ioflags & BIO_ERROR) != 0)
 558                                 error = EIO;
 559
 560                         /*
 561                          * free the buffer header back to the swap buffer pool
 562                          */
 563                         bp->b_vp = NULL;
 564                         pbrelbo(bp);
 565                         relpbuf(bp, &vnode_pbuf_freecnt);
 566                         if (error)
 567                                 break;
 568                 } else
 569                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
 570                 KASSERT((m->dirty & bits) == 0,
 571                     ("vnode_pager_input_smlfs: page %p is dirty", m));
 572                 VM_OBJECT_LOCK(object);
 573                 m->valid |= bits;
 574                 VM_OBJECT_UNLOCK(object);
 575         }
 576         sf_buf_free(sf);
 577         if (error) {
 578                 return VM_PAGER_ERROR;
 579         }
 580         return VM_PAGER_OK;
 581 }
 582
 583 /*
 584  * old style vnode pager input routine
 585  */
 586 static int
 587 vnode_pager_input_old(object, m)
 588         vm_object_t object;
 589         vm_page_t m;
 590 {
 591         struct uio auio;
 592         struct iovec aiov;
 593         int error;
 594         int size;
 595         struct sf_buf *sf;
 596         struct vnode *vp;
 597
 598         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 599         error = 0;
 600
 601         /*
 602          * Return failure if beyond current EOF
 603          */
 604         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
 605                 return VM_PAGER_BAD;
 606         } else {
 607                 size = PAGE_SIZE;
 608                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
 609                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
 610                 vp = object->handle;
 611                 VM_OBJECT_UNLOCK(object);
 612
 613                 /*
 614                  * Allocate a kernel virtual address and initialize so that
 615                  * we can use VOP_READ/WRITE routines.
 616                  */
 617                 sf = sf_buf_alloc(m, 0);
 618
 619                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
 620                 aiov.iov_len = size;
 621                 auio.uio_iov = &aiov;
 622                 auio.uio_iovcnt = 1;
 623                 auio.uio_offset = IDX_TO_OFF(m->pindex);
 624                 auio.uio_segflg = UIO_SYSSPACE;
 625                 auio.uio_rw = UIO_READ;
 626                 auio.uio_resid = size;
 627                 auio.uio_td = curthread;
 628
 629                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
 630                 if (!error) {
 631                         int count = size - auio.uio_resid;
 632
 633                         if (count == 0)
 634                                 error = EINVAL;
 635                         else if (count != PAGE_SIZE)
 636                                 bzero((caddr_t)sf_buf_kva(sf) + count,
 637                                     PAGE_SIZE - count);
 638                 }
 639                 sf_buf_free(sf);
 640
 641                 VM_OBJECT_LOCK(object);
 642         }
 643         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
 644         if (!error)
 645                 m->valid = VM_PAGE_BITS_ALL;
 646         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
 647 }
 648
 649 /*
 650  * generic vnode pager input routine
 651  */
 652
 653 /*
 654  * Local media VFS's that do not implement their own VOP_GETPAGES
 655  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 656  * to implement the previous behaviour.
 657  *
 658  * All other FS's should use the bypass to get to the local media
 659  * backing vp's VOP_GETPAGES.
 660  */
 661 static int
 662 vnode_pager_getpages(object, m, count, reqpage)
 663         vm_object_t object;
 664         vm_page_t *m;
 665         int count;
 666         int reqpage;
 667 {
 668         int rtval;
 669         struct vnode *vp;
 670         int bytes = count * PAGE_SIZE;
 671         int vfslocked;
 672
 673         vp = object->handle;
 674         VM_OBJECT_UNLOCK(object);
 675         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 676         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
 677         KASSERT(rtval != EOPNOTSUPP,
 678             ("vnode_pager: FS getpages not implemented\n"));
 679         VFS_UNLOCK_GIANT(vfslocked);
 680         VM_OBJECT_LOCK(object);
 681         return rtval;
 682 }
 683
 684 /*
 685  * This is now called from local media FS's to operate against their
 686  * own vnodes if they fail to implement VOP_GETPAGES.
 687  */
 688 int
 689 vnode_pager_generic_getpages(vp, m, bytecount, reqpage)
 690         struct vnode *vp;
 691         vm_page_t *m;
 692         int bytecount;
 693         int reqpage;
 694 {
 695         vm_object_t object;
 696         vm_offset_t kva;
 697         off_t foff, tfoff, nextoff;
 698         int i, j, size, bsize, first;
 699         daddr_t firstaddr, reqblock;
 700         struct bufobj *bo;
 701         int runpg;
 702         int runend;
 703         struct buf *bp;
 704         int count;
 705         int error;
 706
 707         object = vp->v_object;
 708         count = bytecount / PAGE_SIZE;
 709
 710         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
 711             ("vnode_pager_generic_getpages does not support devices"));
 712         if (vp->v_iflag & VI_DOOMED)
 713                 return VM_PAGER_BAD;
 714
 715         bsize = vp->v_mount->mnt_stat.f_iosize;
 716
 717         /* get the UNDERLYING device for the file with VOP_BMAP() */
 718
 719         /*
 720          * originally, we did not check for an error return value -- assuming
 721          * an fs always has a bmap entry point -- that assumption is wrong!!!
 722          */
 723         foff = IDX_TO_OFF(m[reqpage]->pindex);
 724
 725         /*
 726          * if we can't bmap, use old VOP code
 727          */
 728         error = VOP_BMAP(vp, foff / bsize, &bo, &reqblock, NULL, NULL);
 729         if (error == EOPNOTSUPP) {
 730                 VM_OBJECT_LOCK(object);
 731
 732                 for (i = 0; i < count; i++)
 733                         if (i != reqpage) {
 734                                 vm_page_lock(m[i]);
 735                                 vm_page_free(m[i]);
 736                                 vm_page_unlock(m[i]);
 737                         }
 738                 PCPU_INC(cnt.v_vnodein);
 739                 PCPU_INC(cnt.v_vnodepgsin);
 740                 error = vnode_pager_input_old(object, m[reqpage]);
 741                 VM_OBJECT_UNLOCK(object);
 742                 return (error);
 743         } else if (error != 0) {
 744                 VM_OBJECT_LOCK(object);
 745                 for (i = 0; i < count; i++)
 746                         if (i != reqpage) {
 747                                 vm_page_lock(m[i]);
 748                                 vm_page_free(m[i]);
 749                                 vm_page_unlock(m[i]);
 750                         }
 751                 VM_OBJECT_UNLOCK(object);
 752                 return (VM_PAGER_ERROR);
 753
 754                 /*
 755                  * if the blocksize is smaller than a page size, then use
 756                  * special small filesystem code.  NFS sometimes has a small
 757                  * blocksize, but it can handle large reads itself.
 758                  */
 759         } else if ((PAGE_SIZE / bsize) > 1 &&
 760             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
 761                 VM_OBJECT_LOCK(object);
 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_UNLOCK(object);
 769                 PCPU_INC(cnt.v_vnodein);
 770                 PCPU_INC(cnt.v_vnodepgsin);
 771                 return vnode_pager_input_smlfs(object, m[reqpage]);
 772         }
 773
 774         /*
 775          * If we have a completely valid page available to us, we can
 776          * clean up and return.  Otherwise we have to re-read the
 777          * media.
 778          */
 779         VM_OBJECT_LOCK(object);
 780         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
 781                 for (i = 0; i < count; i++)
 782                         if (i != reqpage) {
 783                                 vm_page_lock(m[i]);
 784                                 vm_page_free(m[i]);
 785                                 vm_page_unlock(m[i]);
 786                         }
 787                 VM_OBJECT_UNLOCK(object);
 788                 return VM_PAGER_OK;
 789         } else if (reqblock == -1) {
 790                 pmap_zero_page(m[reqpage]);
 791                 KASSERT(m[reqpage]->dirty == 0,
 792                     ("vnode_pager_generic_getpages: page %p is dirty", m));
 793                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
 794                 for (i = 0; i < count; i++)
 795                         if (i != reqpage) {
 796                                 vm_page_lock(m[i]);
 797                                 vm_page_free(m[i]);
 798                                 vm_page_unlock(m[i]);
 799                         }
 800                 VM_OBJECT_UNLOCK(object);
 801                 return (VM_PAGER_OK);
 802         }
 803         m[reqpage]->valid = 0;
 804         VM_OBJECT_UNLOCK(object);
 805
 806         /*
 807          * here on direct device I/O
 808          */
 809         firstaddr = -1;
 810
 811         /*
 812          * calculate the run that includes the required page
 813          */
 814         for (first = 0, i = 0; i < count; i = runend) {
 815                 if (vnode_pager_addr(vp, IDX_TO_OFF(m[i]->pindex), &firstaddr,
 816                     &runpg) != 0) {
 817                         VM_OBJECT_LOCK(object);
 818                         for (; i < count; i++)
 819                                 if (i != reqpage) {
 820                                         vm_page_lock(m[i]);
 821                                         vm_page_free(m[i]);
 822                                         vm_page_unlock(m[i]);
 823                                 }
 824                         VM_OBJECT_UNLOCK(object);
 825                         return (VM_PAGER_ERROR);
 826                 }
 827                 if (firstaddr == -1) {
 828                         VM_OBJECT_LOCK(object);
 829                         if (i == reqpage && foff < object->un_pager.vnp.vnp_size) {
 830                                 panic("vnode_pager_getpages: unexpected missing page: firstaddr: %jd, foff: 0x%jx%08jx, vnp_size: 0x%jx%08jx",
 831                                     (intmax_t)firstaddr, (uintmax_t)(foff >> 32),
 832                                     (uintmax_t)foff,
 833                                     (uintmax_t)
 834                                     (object->un_pager.vnp.vnp_size >> 32),
 835                                     (uintmax_t)object->un_pager.vnp.vnp_size);
 836                         }
 837                         vm_page_lock(m[i]);
 838                         vm_page_free(m[i]);
 839                         vm_page_unlock(m[i]);
 840                         VM_OBJECT_UNLOCK(object);
 841                         runend = i + 1;
 842                         first = runend;
 843                         continue;
 844                 }
 845                 runend = i + runpg;
 846                 if (runend <= reqpage) {
 847                         VM_OBJECT_LOCK(object);
 848                         for (j = i; j < runend; j++) {
 849                                 vm_page_lock(m[j]);
 850                                 vm_page_free(m[j]);
 851                                 vm_page_unlock(m[j]);
 852                         }
 853                         VM_OBJECT_UNLOCK(object);
 854                 } else {
 855                         if (runpg < (count - first)) {
 856                                 VM_OBJECT_LOCK(object);
 857                                 for (i = first + runpg; i < count; i++) {
 858                                         vm_page_lock(m[i]);
 859                                         vm_page_free(m[i]);
 860                                         vm_page_unlock(m[i]);
 861                                 }
 862                                 VM_OBJECT_UNLOCK(object);
 863                                 count = first + runpg;
 864                         }
 865                         break;
 866                 }
 867                 first = runend;
 868         }
 869
 870         /*
 871          * the first and last page have been calculated now, move input pages
 872          * to be zero based...
 873          */
 874         if (first != 0) {
 875                 m += first;
 876                 count -= first;
 877                 reqpage -= first;
 878         }
 879
 880         /*
 881          * calculate the file virtual address for the transfer
 882          */
 883         foff = IDX_TO_OFF(m[0]->pindex);
 884
 885         /*
 886          * calculate the size of the transfer
 887          */
 888         size = count * PAGE_SIZE;
 889         KASSERT(count > 0, ("zero count"));
 890         if ((foff + size) > object->un_pager.vnp.vnp_size)
 891                 size = object->un_pager.vnp.vnp_size - foff;
 892         KASSERT(size > 0, ("zero size"));
 893
 894         /*
 895          * round up physical size for real devices.
 896          */
 897         if (1) {
 898                 int secmask = bo->bo_bsize - 1;
 899                 KASSERT(secmask < PAGE_SIZE && secmask > 0,
 900                     ("vnode_pager_generic_getpages: sector size %d too large",
 901                     secmask + 1));
 902                 size = (size + secmask) & ~secmask;
 903         }
 904
 905         bp = getpbuf(&vnode_pbuf_freecnt);
 906         kva = (vm_offset_t) bp->b_data;
 907
 908         /*
 909          * and map the pages to be read into the kva
 910          */
 911         pmap_qenter(kva, m, count);
 912
 913         /* build a minimal buffer header */
 914         bp->b_iocmd = BIO_READ;
 915         bp->b_iodone = bdone;
 916         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 917         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 918         bp->b_rcred = crhold(curthread->td_ucred);
 919         bp->b_wcred = crhold(curthread->td_ucred);
 920         bp->b_blkno = firstaddr;
 921         pbgetbo(bo, bp);
 922         bp->b_vp = vp;
 923         bp->b_bcount = size;
 924         bp->b_bufsize = size;
 925         bp->b_runningbufspace = bp->b_bufsize;
 926         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 927
 928         PCPU_INC(cnt.v_vnodein);
 929         PCPU_ADD(cnt.v_vnodepgsin, count);
 930
 931         /* do the input */
 932         bp->b_iooffset = dbtob(bp->b_blkno);
 933         bstrategy(bp);
 934
 935         bwait(bp, PVM, "vnread");
 936
 937         if ((bp->b_ioflags & BIO_ERROR) != 0)
 938                 error = EIO;
 939
 940         if (!error) {
 941                 if (size != count * PAGE_SIZE)
 942                         bzero((caddr_t) kva + size, PAGE_SIZE * count - size);
 943         }
 944         pmap_qremove(kva, count);
 945
 946         /*
 947          * free the buffer header back to the swap buffer pool
 948          */
 949         bp->b_vp = NULL;
 950         pbrelbo(bp);
 951         relpbuf(bp, &vnode_pbuf_freecnt);
 952
 953         VM_OBJECT_LOCK(object);
 954         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
 955                 vm_page_t mt;
 956
 957                 nextoff = tfoff + PAGE_SIZE;
 958                 mt = m[i];
 959
 960                 if (nextoff <= object->un_pager.vnp.vnp_size) {
 961                         /*
 962                          * Read filled up entire page.
 963                          */
 964                         mt->valid = VM_PAGE_BITS_ALL;
 965                         KASSERT(mt->dirty == 0,
 966                             ("vnode_pager_generic_getpages: page %p is dirty",
 967                             mt));
 968                         KASSERT(!pmap_page_is_mapped(mt),
 969                             ("vnode_pager_generic_getpages: page %p is mapped",
 970                             mt));
 971                 } else {
 972                         /*
 973                          * Read did not fill up entire page.
 974                          *
 975                          * Currently we do not set the entire page valid,
 976                          * we just try to clear the piece that we couldn't
 977                          * read.
 978                          */
 979                         vm_page_set_valid(mt, 0,
 980                             object->un_pager.vnp.vnp_size - tfoff);
 981                         KASSERT((mt->dirty & vm_page_bits(0,
 982                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
 983                             ("vnode_pager_generic_getpages: page %p is dirty",
 984                             mt));
 985                 }
 986
 987                 if (i != reqpage)
 988                         vm_page_readahead_finish(mt);
 989         }
 990         VM_OBJECT_UNLOCK(object);
 991         if (error) {
 992                 printf("vnode_pager_getpages: I/O read error\n");
 993         }
 994         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
 995 }
 996
 997 /*
 998  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
 999  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
1000  * vnode_pager_generic_putpages() to implement the previous behaviour.
1001  *
1002  * All other FS's should use the bypass to get to the local media
1003  * backing vp's VOP_PUTPAGES.
1004  */
1005 static void
1006 vnode_pager_putpages(object, m, count, sync, rtvals)
1007         vm_object_t object;
1008         vm_page_t *m;
1009         int count;
1010         boolean_t sync;
1011         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 ((cnt.v_free_count + cnt.v_cache_count) < cnt.v_pageout_free_min)
1030                 sync |= OBJPC_SYNC;
1031
1032         /*
1033          * Call device-specific putpages function
1034          */
1035         vp = object->handle;
1036         VM_OBJECT_UNLOCK(object);
1037         rtval = VOP_PUTPAGES(vp, m, bytes, sync, rtvals, 0);
1038         KASSERT(rtval != EOPNOTSUPP,
1039             ("vnode_pager: stale FS putpages\n"));
1040         VM_OBJECT_LOCK(object);
1041 }
1042
1043
1044 /*
1045  * This is now called from local media FS's to operate against their
1046  * own vnodes if they fail to implement VOP_PUTPAGES.
1047  *
1048  * This is typically called indirectly via the pageout daemon and
1049  * clustering has already typically occured, so in general we ask the
1050  * underlying filesystem to write the data out asynchronously rather
1051  * then delayed.
1052  */
1053 int
1054 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
1055     int flags, int *rtvals)
1056 {
1057         int i;
1058         vm_object_t object;
1059         vm_page_t m;
1060         int count;
1061
1062         int maxsize, ncount;
1063         vm_ooffset_t poffset;
1064         struct uio auio;
1065         struct iovec aiov;
1066         int error;
1067         int ioflags;
1068         int ppscheck = 0;
1069         static struct timeval lastfail;
1070         static int curfail;
1071
1072         object = vp->v_object;
1073         count = bytecount / PAGE_SIZE;
1074
1075         for (i = 0; i < count; i++)
1076                 rtvals[i] = VM_PAGER_ERROR;
1077
1078         if ((int64_t)ma[0]->pindex < 0) {
1079                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
1080                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
1081                 rtvals[0] = VM_PAGER_BAD;
1082                 return VM_PAGER_BAD;
1083         }
1084
1085         maxsize = count * PAGE_SIZE;
1086         ncount = count;
1087
1088         poffset = IDX_TO_OFF(ma[0]->pindex);
1089
1090         /*
1091          * If the page-aligned write is larger then the actual file we
1092          * have to invalidate pages occuring beyond the file EOF.  However,
1093          * there is an edge case where a file may not be page-aligned where
1094          * the last page is partially invalid.  In this case the filesystem
1095          * may not properly clear the dirty bits for the entire page (which
1096          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
1097          * With the page locked we are free to fix-up the dirty bits here.
1098          *
1099          * We do not under any circumstances truncate the valid bits, as
1100          * this will screw up bogus page replacement.
1101          */
1102         VM_OBJECT_LOCK(object);
1103         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
1104                 if (object->un_pager.vnp.vnp_size > poffset) {
1105                         int pgoff;
1106
1107                         maxsize = object->un_pager.vnp.vnp_size - poffset;
1108                         ncount = btoc(maxsize);
1109                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
1110                                 /*
1111                                  * If the object is locked and the following
1112                                  * conditions hold, then the page's dirty
1113                                  * field cannot be concurrently changed by a
1114                                  * pmap operation.
1115                                  */
1116                                 m = ma[ncount - 1];
1117                                 KASSERT(m->busy > 0,
1118                 ("vnode_pager_generic_putpages: page %p is not busy", 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_UNLOCK(object);
1135
1136         /*
1137          * pageouts are already clustered, use IO_ASYNC t o 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_LOCK(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_UNLOCK(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_LOCK(object);
1210         if (object->type != OBJT_VNODE) {
1211                 VM_OBJECT_UNLOCK(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         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
1221                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
1222                 VOP_ADD_WRITECOUNT(vp, -1);
1223         }
1224         VM_OBJECT_UNLOCK(object);
1225 }
1226
1227 void
1228 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
1229     vm_offset_t end)
1230 {
1231         struct vnode *vp;
1232         struct mount *mp;
1233         vm_offset_t inc;
1234         int vfslocked;
1235
1236         VM_OBJECT_LOCK(object);
1237
1238         /*
1239          * First, recheck the object type to account for the race when
1240          * the vnode is reclaimed.
1241          */
1242         if (object->type != OBJT_VNODE) {
1243                 VM_OBJECT_UNLOCK(object);
1244                 return;
1245         }
1246
1247         /*
1248          * Optimize for the case when writemappings is not going to
1249          * zero.
1250          */
1251         inc = end - start;
1252         if (object->un_pager.vnp.writemappings != inc) {
1253                 object->un_pager.vnp.writemappings -= inc;
1254                 VM_OBJECT_UNLOCK(object);
1255                 return;
1256         }
1257
1258         vp = object->handle;
1259         vhold(vp);
1260         VM_OBJECT_UNLOCK(object);
1261         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
1262         mp = NULL;
1263         vn_start_write(vp, &mp, V_WAIT);
1264         vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
1265
1266         /*
1267          * Decrement the object's writemappings, by swapping the start
1268          * and end arguments for vnode_pager_update_writecount().  If
1269          * there was not a race with vnode reclaimation, then the
1270          * vnode's v_writecount is decremented.
1271          */
1272         vnode_pager_update_writecount(object, end, start);
1273         VOP_UNLOCK(vp, 0);
1274         vdrop(vp);
1275         if (mp != NULL)
1276                 vn_finished_write(mp);
1277         VFS_UNLOCK_GIANT(vfslocked);
1278 }