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_object.h>
  72 #include <vm/vm_page.h>
  73 #include <vm/vm_pager.h>
  74 #include <vm/vm_map.h>
  75 #include <vm/vnode_pager.h>
  76 #include <vm/vm_extern.h>
  77
  78 static int vnode_pager_addr(struct vnode *vp, vm_ooffset_t address,
  79     daddr_t *rtaddress, int *run);
  80 static int vnode_pager_input_smlfs(vm_object_t object, vm_page_t m);
  81 static int vnode_pager_input_old(vm_object_t object, vm_page_t m);
  82 static void vnode_pager_dealloc(vm_object_t);
  83 static int vnode_pager_getpages(vm_object_t, vm_page_t *, int, int);
  84 static void vnode_pager_putpages(vm_object_t, vm_page_t *, int, boolean_t, int *);
  85 static boolean_t vnode_pager_haspage(vm_object_t, vm_pindex_t, int *, int *);
  86 static vm_object_t vnode_pager_alloc(void *, vm_ooffset_t, vm_prot_t,
  87     vm_ooffset_t, struct ucred *cred);
  88
  89 struct pagerops vnodepagerops = {
  90         .pgo_alloc =    vnode_pager_alloc,
  91         .pgo_dealloc =  vnode_pager_dealloc,
  92         .pgo_getpages = vnode_pager_getpages,
  93         .pgo_putpages = vnode_pager_putpages,
  94         .pgo_haspage =  vnode_pager_haspage,
  95 };
  96
  97 int vnode_pbuf_freecnt;
  98
  99 /* Create the VM system backing object for this vnode */
 100 int
 101 vnode_create_vobject(struct vnode *vp, off_t isize, struct thread *td)
 102 {
 103         vm_object_t object;
 104         vm_ooffset_t size = isize;
 105         struct vattr va;
 106
 107         if (!vn_isdisk(vp, NULL) && vn_canvmio(vp) == FALSE)
 108                 return (0);
 109
 110         while ((object = vp->v_object) != NULL) {
 111                 VM_OBJECT_LOCK(object);
 112                 if (!(object->flags & OBJ_DEAD)) {
 113                         VM_OBJECT_UNLOCK(object);
 114                         return (0);
 115                 }
 116                 VOP_UNLOCK(vp, 0);
 117                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 118                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vodead", 0);
 119                 vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 120         }
 121
 122         if (size == 0) {
 123                 if (vn_isdisk(vp, NULL)) {
 124                         size = IDX_TO_OFF(INT_MAX);
 125                 } else {
 126                         if (VOP_GETATTR(vp, &va, td->td_ucred))
 127                                 return (0);
 128                         size = va.va_size;
 129                 }
 130         }
 131
 132         object = vnode_pager_alloc(vp, size, 0, 0, td->td_ucred);
 133         /*
 134          * Dereference the reference we just created.  This assumes
 135          * that the object is associated with the vp.
 136          */
 137         VM_OBJECT_LOCK(object);
 138         object->ref_count--;
 139         VM_OBJECT_UNLOCK(object);
 140         vrele(vp);
 141
 142         KASSERT(vp->v_object != NULL, ("vnode_create_vobject: NULL object"));
 143
 144         return (0);
 145 }
 146
 147 void
 148 vnode_destroy_vobject(struct vnode *vp)
 149 {
 150         struct vm_object *obj;
 151
 152         obj = vp->v_object;
 153         if (obj == NULL)
 154                 return;
 155         ASSERT_VOP_ELOCKED(vp, "vnode_destroy_vobject");
 156         VM_OBJECT_LOCK(obj);
 157         if (obj->ref_count == 0) {
 158                 /*
 159                  * vclean() may be called twice. The first time
 160                  * removes the primary reference to the object,
 161                  * the second time goes one further and is a
 162                  * special-case to terminate the object.
 163                  *
 164                  * don't double-terminate the object
 165                  */
 166                 if ((obj->flags & OBJ_DEAD) == 0)
 167                         vm_object_terminate(obj);
 168                 else
 169                         VM_OBJECT_UNLOCK(obj);
 170         } else {
 171                 /*
 172                  * Woe to the process that tries to page now :-).
 173                  */
 174                 vm_pager_deallocate(obj);
 175                 VM_OBJECT_UNLOCK(obj);
 176         }
 177         vp->v_object = NULL;
 178 }
 179
 180
 181 /*
 182  * Allocate (or lookup) pager for a vnode.
 183  * Handle is a vnode pointer.
 184  *
 185  * MPSAFE
 186  */
 187 vm_object_t
 188 vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 189     vm_ooffset_t offset, struct ucred *cred)
 190 {
 191         vm_object_t object;
 192         struct vnode *vp;
 193
 194         /*
 195          * Pageout to vnode, no can do yet.
 196          */
 197         if (handle == NULL)
 198                 return (NULL);
 199
 200         vp = (struct vnode *) handle;
 201
 202         /*
 203          * If the object is being terminated, wait for it to
 204          * go away.
 205          */
 206 retry:
 207         while ((object = vp->v_object) != NULL) {
 208                 VM_OBJECT_LOCK(object);
 209                 if ((object->flags & OBJ_DEAD) == 0)
 210                         break;
 211                 vm_object_set_flag(object, OBJ_DISCONNECTWNT);
 212                 msleep(object, VM_OBJECT_MTX(object), PDROP | PVM, "vadead", 0);
 213         }
 214
 215         if (vp->v_usecount == 0)
 216                 panic("vnode_pager_alloc: no vnode reference");
 217
 218         if (object == NULL) {
 219                 /*
 220                  * Add an object of the appropriate size
 221                  */
 222                 object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
 223
 224                 object->un_pager.vnp.vnp_size = size;
 225                 object->un_pager.vnp.writemappings = 0;
 226
 227                 object->handle = handle;
 228                 VI_LOCK(vp);
 229                 if (vp->v_object != NULL) {
 230                         /*
 231                          * Object has been created while we were sleeping
 232                          */
 233                         VI_UNLOCK(vp);
 234                         vm_object_destroy(object);
 235                         goto retry;
 236                 }
 237                 vp->v_object = object;
 238                 VI_UNLOCK(vp);
 239         } else {
 240                 object->ref_count++;
 241                 VM_OBJECT_UNLOCK(object);
 242         }
 243         vref(vp);
 244         return (object);
 245 }
 246
 247 /*
 248  *      The object must be locked.
 249  */
 250 static void
 251 vnode_pager_dealloc(object)
 252         vm_object_t object;
 253 {
 254         struct vnode *vp;
 255         int refs;
 256
 257         vp = object->handle;
 258         if (vp == NULL)
 259                 panic("vnode_pager_dealloc: pager already dealloced");
 260
 261         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 262         vm_object_pip_wait(object, "vnpdea");
 263         refs = object->ref_count;
 264
 265         object->handle = NULL;
 266         object->type = OBJT_DEAD;
 267         if (object->flags & OBJ_DISCONNECTWNT) {
 268                 vm_object_clear_flag(object, OBJ_DISCONNECTWNT);
 269                 wakeup(object);
 270         }
 271         ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
 272         if (object->un_pager.vnp.writemappings > 0) {
 273                 object->un_pager.vnp.writemappings = 0;
 274                 vp->v_writecount--;
 275         }
 276         vp->v_object = NULL;
 277         vp->v_vflag &= ~VV_TEXT;
 278         VM_OBJECT_UNLOCK(object);
 279         while (refs-- > 0)
 280                 vunref(vp);
 281         VM_OBJECT_LOCK(object);
 282 }
 283
 284 static boolean_t
 285 vnode_pager_haspage(object, pindex, before, after)
 286         vm_object_t object;
 287         vm_pindex_t pindex;
 288         int *before;
 289         int *after;
 290 {
 291         struct vnode *vp = object->handle;
 292         daddr_t bn;
 293         int err;
 294         daddr_t reqblock;
 295         int poff;
 296         int bsize;
 297         int pagesperblock, blocksperpage;
 298         int vfslocked;
 299
 300         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 301         /*
 302          * If no vp or vp is doomed or marked transparent to VM, we do not
 303          * have the page.
 304          */
 305         if (vp == NULL || vp->v_iflag & VI_DOOMED)
 306                 return FALSE;
 307         /*
 308          * If the offset is beyond end of file we do
 309          * not have the page.
 310          */
 311         if (IDX_TO_OFF(pindex) >= object->un_pager.vnp.vnp_size)
 312                 return FALSE;
 313
 314         bsize = vp->v_mount->mnt_stat.f_iosize;
 315         pagesperblock = bsize / PAGE_SIZE;
 316         blocksperpage = 0;
 317         if (pagesperblock > 0) {
 318                 reqblock = pindex / pagesperblock;
 319         } else {
 320                 blocksperpage = (PAGE_SIZE / bsize);
 321                 reqblock = pindex * blocksperpage;
 322         }
 323         VM_OBJECT_UNLOCK(object);
 324         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 325         err = VOP_BMAP(vp, reqblock, NULL, &bn, after, before);
 326         VFS_UNLOCK_GIANT(vfslocked);
 327         VM_OBJECT_LOCK(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_LOCK(object);
 383         if (nsize == object->un_pager.vnp.vnp_size) {
 384                 /*
 385                  * Hasn't changed size
 386                  */
 387                 VM_OBJECT_UNLOCK(object);
 388                 return;
 389         }
 390         nobjsize = OFF_TO_IDX(nsize + PAGE_MASK);
 391         if (nsize < object->un_pager.vnp.vnp_size) {
 392                 /*
 393                  * File has shrunk. Toss any cached pages beyond the new EOF.
 394                  */
 395                 if (nobjsize < object->size)
 396                         vm_object_page_remove(object, nobjsize, object->size,
 397                             0);
 398                 /*
 399                  * this gets rid of garbage at the end of a page that is now
 400                  * only partially backed by the vnode.
 401                  *
 402                  * XXX for some reason (I don't know yet), if we take a
 403                  * completely invalid page and mark it partially valid
 404                  * it can screw up NFS reads, so we don't allow the case.
 405                  */
 406                 if ((nsize & PAGE_MASK) &&
 407                     (m = vm_page_lookup(object, OFF_TO_IDX(nsize))) != NULL &&
 408                     m->valid != 0) {
 409                         int base = (int)nsize & PAGE_MASK;
 410                         int size = PAGE_SIZE - base;
 411
 412                         /*
 413                          * Clear out partial-page garbage in case
 414                          * the page has been mapped.
 415                          */
 416                         pmap_zero_page_area(m, base, size);
 417
 418                         /*
 419                          * Update the valid bits to reflect the blocks that
 420                          * have been zeroed.  Some of these valid bits may
 421                          * have already been set.
 422                          */
 423                         vm_page_set_valid(m, base, size);
 424
 425                         /*
 426                          * Round "base" to the next block boundary so that the
 427                          * dirty bit for a partially zeroed block is not
 428                          * cleared.
 429                          */
 430                         base = roundup2(base, DEV_BSIZE);
 431
 432                         /*
 433                          * Clear out partial-page dirty bits.
 434                          *
 435                          * note that we do not clear out the valid
 436                          * bits.  This would prevent bogus_page
 437                          * replacement from working properly.
 438                          */
 439                         vm_page_clear_dirty(m, base, PAGE_SIZE - base);
 440                 } else if ((nsize & PAGE_MASK) &&
 441                     __predict_false(object->cache != NULL)) {
 442                         vm_page_cache_free(object, OFF_TO_IDX(nsize),
 443                             nobjsize);
 444                 }
 445         }
 446         object->un_pager.vnp.vnp_size = nsize;
 447         object->size = nobjsize;
 448         VM_OBJECT_UNLOCK(object);
 449 }
 450
 451 /*
 452  * calculate the linear (byte) disk address of specified virtual
 453  * file address
 454  */
 455 static int
 456 vnode_pager_addr(struct vnode *vp, vm_ooffset_t address, daddr_t *rtaddress,
 457     int *run)
 458 {
 459         int bsize;
 460         int err;
 461         daddr_t vblock;
 462         daddr_t voffset;
 463
 464         if (address < 0)
 465                 return -1;
 466
 467         if (vp->v_iflag & VI_DOOMED)
 468                 return -1;
 469
 470         bsize = vp->v_mount->mnt_stat.f_iosize;
 471         vblock = address / bsize;
 472         voffset = address % bsize;
 473
 474         err = VOP_BMAP(vp, vblock, NULL, rtaddress, run, NULL);
 475         if (err == 0) {
 476                 if (*rtaddress != -1)
 477                         *rtaddress += voffset / DEV_BSIZE;
 478                 if (run) {
 479                         *run += 1;
 480                         *run *= bsize/PAGE_SIZE;
 481                         *run -= voffset/PAGE_SIZE;
 482                 }
 483         }
 484
 485         return (err);
 486 }
 487
 488 /*
 489  * small block filesystem vnode pager input
 490  */
 491 static int
 492 vnode_pager_input_smlfs(object, m)
 493         vm_object_t object;
 494         vm_page_t m;
 495 {
 496         struct vnode *vp;
 497         struct bufobj *bo;
 498         struct buf *bp;
 499         struct sf_buf *sf;
 500         daddr_t fileaddr;
 501         vm_offset_t bsize;
 502         vm_page_bits_t bits;
 503         int error, i;
 504
 505         error = 0;
 506         vp = object->handle;
 507         if (vp->v_iflag & VI_DOOMED)
 508                 return VM_PAGER_BAD;
 509
 510         bsize = vp->v_mount->mnt_stat.f_iosize;
 511
 512         VOP_BMAP(vp, 0, &bo, 0, NULL, NULL);
 513
 514         sf = sf_buf_alloc(m, 0);
 515
 516         for (i = 0; i < PAGE_SIZE / bsize; i++) {
 517                 vm_ooffset_t address;
 518
 519                 bits = vm_page_bits(i * bsize, bsize);
 520                 if (m->valid & bits)
 521                         continue;
 522
 523                 address = IDX_TO_OFF(m->pindex) + i * bsize;
 524                 if (address >= object->un_pager.vnp.vnp_size) {
 525                         fileaddr = -1;
 526                 } else {
 527                         error = vnode_pager_addr(vp, address, &fileaddr, NULL);
 528                         if (error)
 529                                 break;
 530                 }
 531                 if (fileaddr != -1) {
 532                         bp = getpbuf(&vnode_pbuf_freecnt);
 533
 534                         /* build a minimal buffer header */
 535                         bp->b_iocmd = BIO_READ;
 536                         bp->b_iodone = bdone;
 537                         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 538                         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 539                         bp->b_rcred = crhold(curthread->td_ucred);
 540                         bp->b_wcred = crhold(curthread->td_ucred);
 541                         bp->b_data = (caddr_t)sf_buf_kva(sf) + i * bsize;
 542                         bp->b_blkno = fileaddr;
 543                         pbgetbo(bo, bp);
 544                         bp->b_vp = vp;
 545                         bp->b_bcount = bsize;
 546                         bp->b_bufsize = bsize;
 547                         bp->b_runningbufspace = bp->b_bufsize;
 548                         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 549
 550                         /* do the input */
 551                         bp->b_iooffset = dbtob(bp->b_blkno);
 552                         bstrategy(bp);
 553
 554                         bwait(bp, PVM, "vnsrd");
 555
 556                         if ((bp->b_ioflags & BIO_ERROR) != 0)
 557                                 error = EIO;
 558
 559                         /*
 560                          * free the buffer header back to the swap buffer pool
 561                          */
 562                         bp->b_vp = NULL;
 563                         pbrelbo(bp);
 564                         relpbuf(bp, &vnode_pbuf_freecnt);
 565                         if (error)
 566                                 break;
 567                 } else
 568                         bzero((caddr_t)sf_buf_kva(sf) + i * bsize, bsize);
 569                 KASSERT((m->dirty & bits) == 0,
 570                     ("vnode_pager_input_smlfs: page %p is dirty", m));
 571                 VM_OBJECT_LOCK(object);
 572                 m->valid |= bits;
 573                 VM_OBJECT_UNLOCK(object);
 574         }
 575         sf_buf_free(sf);
 576         if (error) {
 577                 return VM_PAGER_ERROR;
 578         }
 579         return VM_PAGER_OK;
 580 }
 581
 582 /*
 583  * old style vnode pager input routine
 584  */
 585 static int
 586 vnode_pager_input_old(object, m)
 587         vm_object_t object;
 588         vm_page_t m;
 589 {
 590         struct uio auio;
 591         struct iovec aiov;
 592         int error;
 593         int size;
 594         struct sf_buf *sf;
 595         struct vnode *vp;
 596
 597         VM_OBJECT_LOCK_ASSERT(object, MA_OWNED);
 598         error = 0;
 599
 600         /*
 601          * Return failure if beyond current EOF
 602          */
 603         if (IDX_TO_OFF(m->pindex) >= object->un_pager.vnp.vnp_size) {
 604                 return VM_PAGER_BAD;
 605         } else {
 606                 size = PAGE_SIZE;
 607                 if (IDX_TO_OFF(m->pindex) + size > object->un_pager.vnp.vnp_size)
 608                         size = object->un_pager.vnp.vnp_size - IDX_TO_OFF(m->pindex);
 609                 vp = object->handle;
 610                 VM_OBJECT_UNLOCK(object);
 611
 612                 /*
 613                  * Allocate a kernel virtual address and initialize so that
 614                  * we can use VOP_READ/WRITE routines.
 615                  */
 616                 sf = sf_buf_alloc(m, 0);
 617
 618                 aiov.iov_base = (caddr_t)sf_buf_kva(sf);
 619                 aiov.iov_len = size;
 620                 auio.uio_iov = &aiov;
 621                 auio.uio_iovcnt = 1;
 622                 auio.uio_offset = IDX_TO_OFF(m->pindex);
 623                 auio.uio_segflg = UIO_SYSSPACE;
 624                 auio.uio_rw = UIO_READ;
 625                 auio.uio_resid = size;
 626                 auio.uio_td = curthread;
 627
 628                 error = VOP_READ(vp, &auio, 0, curthread->td_ucred);
 629                 if (!error) {
 630                         int count = size - auio.uio_resid;
 631
 632                         if (count == 0)
 633                                 error = EINVAL;
 634                         else if (count != PAGE_SIZE)
 635                                 bzero((caddr_t)sf_buf_kva(sf) + count,
 636                                     PAGE_SIZE - count);
 637                 }
 638                 sf_buf_free(sf);
 639
 640                 VM_OBJECT_LOCK(object);
 641         }
 642         KASSERT(m->dirty == 0, ("vnode_pager_input_old: page %p is dirty", m));
 643         if (!error)
 644                 m->valid = VM_PAGE_BITS_ALL;
 645         return error ? VM_PAGER_ERROR : VM_PAGER_OK;
 646 }
 647
 648 /*
 649  * generic vnode pager input routine
 650  */
 651
 652 /*
 653  * Local media VFS's that do not implement their own VOP_GETPAGES
 654  * should have their VOP_GETPAGES call to vnode_pager_generic_getpages()
 655  * to implement the previous behaviour.
 656  *
 657  * All other FS's should use the bypass to get to the local media
 658  * backing vp's VOP_GETPAGES.
 659  */
 660 static int
 661 vnode_pager_getpages(object, m, count, reqpage)
 662         vm_object_t object;
 663         vm_page_t *m;
 664         int count;
 665         int reqpage;
 666 {
 667         int rtval;
 668         struct vnode *vp;
 669         int bytes = count * PAGE_SIZE;
 670         int vfslocked;
 671
 672         vp = object->handle;
 673         VM_OBJECT_UNLOCK(object);
 674         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
 675         rtval = VOP_GETPAGES(vp, m, bytes, reqpage, 0);
 676         KASSERT(rtval != EOPNOTSUPP,
 677             ("vnode_pager: FS getpages not implemented\n"));
 678         VFS_UNLOCK_GIANT(vfslocked);
 679         VM_OBJECT_LOCK(object);
 680         return rtval;
 681 }
 682
 683 /*
 684  * This is now called from local media FS's to operate against their
 685  * own vnodes if they fail to implement VOP_GETPAGES.
 686  */
 687 int
 688 vnode_pager_generic_getpages(vp, m, bytecount, reqpage)
 689         struct vnode *vp;
 690         vm_page_t *m;
 691         int bytecount;
 692         int reqpage;
 693 {
 694         vm_object_t object;
 695         vm_offset_t kva;
 696         off_t foff, tfoff, nextoff;
 697         int i, j, size, bsize, first;
 698         daddr_t firstaddr, reqblock;
 699         struct bufobj *bo;
 700         int runpg;
 701         int runend;
 702         struct buf *bp;
 703         int count;
 704         int error;
 705
 706         object = vp->v_object;
 707         count = bytecount / PAGE_SIZE;
 708
 709         KASSERT(vp->v_type != VCHR && vp->v_type != VBLK,
 710             ("vnode_pager_generic_getpages does not support devices"));
 711         if (vp->v_iflag & VI_DOOMED)
 712                 return VM_PAGER_BAD;
 713
 714         bsize = vp->v_mount->mnt_stat.f_iosize;
 715
 716         /* get the UNDERLYING device for the file with VOP_BMAP() */
 717
 718         /*
 719          * originally, we did not check for an error return value -- assuming
 720          * an fs always has a bmap entry point -- that assumption is wrong!!!
 721          */
 722         foff = IDX_TO_OFF(m[reqpage]->pindex);
 723
 724         /*
 725          * if we can't bmap, use old VOP code
 726          */
 727         error = VOP_BMAP(vp, foff / bsize, &bo, &reqblock, NULL, NULL);
 728         if (error == EOPNOTSUPP) {
 729                 VM_OBJECT_LOCK(object);
 730
 731                 for (i = 0; i < count; i++)
 732                         if (i != reqpage) {
 733                                 vm_page_lock(m[i]);
 734                                 vm_page_free(m[i]);
 735                                 vm_page_unlock(m[i]);
 736                         }
 737                 PCPU_INC(cnt.v_vnodein);
 738                 PCPU_INC(cnt.v_vnodepgsin);
 739                 error = vnode_pager_input_old(object, m[reqpage]);
 740                 VM_OBJECT_UNLOCK(object);
 741                 return (error);
 742         } else if (error != 0) {
 743                 VM_OBJECT_LOCK(object);
 744                 for (i = 0; i < count; i++)
 745                         if (i != reqpage) {
 746                                 vm_page_lock(m[i]);
 747                                 vm_page_free(m[i]);
 748                                 vm_page_unlock(m[i]);
 749                         }
 750                 VM_OBJECT_UNLOCK(object);
 751                 return (VM_PAGER_ERROR);
 752
 753                 /*
 754                  * if the blocksize is smaller than a page size, then use
 755                  * special small filesystem code.  NFS sometimes has a small
 756                  * blocksize, but it can handle large reads itself.
 757                  */
 758         } else if ((PAGE_SIZE / bsize) > 1 &&
 759             (vp->v_mount->mnt_stat.f_type != nfs_mount_type)) {
 760                 VM_OBJECT_LOCK(object);
 761                 for (i = 0; i < count; i++)
 762                         if (i != reqpage) {
 763                                 vm_page_lock(m[i]);
 764                                 vm_page_free(m[i]);
 765                                 vm_page_unlock(m[i]);
 766                         }
 767                 VM_OBJECT_UNLOCK(object);
 768                 PCPU_INC(cnt.v_vnodein);
 769                 PCPU_INC(cnt.v_vnodepgsin);
 770                 return vnode_pager_input_smlfs(object, m[reqpage]);
 771         }
 772
 773         /*
 774          * If we have a completely valid page available to us, we can
 775          * clean up and return.  Otherwise we have to re-read the
 776          * media.
 777          */
 778         VM_OBJECT_LOCK(object);
 779         if (m[reqpage]->valid == VM_PAGE_BITS_ALL) {
 780                 for (i = 0; i < count; i++)
 781                         if (i != reqpage) {
 782                                 vm_page_lock(m[i]);
 783                                 vm_page_free(m[i]);
 784                                 vm_page_unlock(m[i]);
 785                         }
 786                 VM_OBJECT_UNLOCK(object);
 787                 return VM_PAGER_OK;
 788         } else if (reqblock == -1) {
 789                 pmap_zero_page(m[reqpage]);
 790                 KASSERT(m[reqpage]->dirty == 0,
 791                     ("vnode_pager_generic_getpages: page %p is dirty", m));
 792                 m[reqpage]->valid = VM_PAGE_BITS_ALL;
 793                 for (i = 0; i < count; i++)
 794                         if (i != reqpage) {
 795                                 vm_page_lock(m[i]);
 796                                 vm_page_free(m[i]);
 797                                 vm_page_unlock(m[i]);
 798                         }
 799                 VM_OBJECT_UNLOCK(object);
 800                 return (VM_PAGER_OK);
 801         }
 802         m[reqpage]->valid = 0;
 803         VM_OBJECT_UNLOCK(object);
 804
 805         /*
 806          * here on direct device I/O
 807          */
 808         firstaddr = -1;
 809
 810         /*
 811          * calculate the run that includes the required page
 812          */
 813         for (first = 0, i = 0; i < count; i = runend) {
 814                 if (vnode_pager_addr(vp, IDX_TO_OFF(m[i]->pindex), &firstaddr,
 815                     &runpg) != 0) {
 816                         VM_OBJECT_LOCK(object);
 817                         for (; i < count; i++)
 818                                 if (i != reqpage) {
 819                                         vm_page_lock(m[i]);
 820                                         vm_page_free(m[i]);
 821                                         vm_page_unlock(m[i]);
 822                                 }
 823                         VM_OBJECT_UNLOCK(object);
 824                         return (VM_PAGER_ERROR);
 825                 }
 826                 if (firstaddr == -1) {
 827                         VM_OBJECT_LOCK(object);
 828                         if (i == reqpage && foff < object->un_pager.vnp.vnp_size) {
 829                                 panic("vnode_pager_getpages: unexpected missing page: firstaddr: %jd, foff: 0x%jx%08jx, vnp_size: 0x%jx%08jx",
 830                                     (intmax_t)firstaddr, (uintmax_t)(foff >> 32),
 831                                     (uintmax_t)foff,
 832                                     (uintmax_t)
 833                                     (object->un_pager.vnp.vnp_size >> 32),
 834                                     (uintmax_t)object->un_pager.vnp.vnp_size);
 835                         }
 836                         vm_page_lock(m[i]);
 837                         vm_page_free(m[i]);
 838                         vm_page_unlock(m[i]);
 839                         VM_OBJECT_UNLOCK(object);
 840                         runend = i + 1;
 841                         first = runend;
 842                         continue;
 843                 }
 844                 runend = i + runpg;
 845                 if (runend <= reqpage) {
 846                         VM_OBJECT_LOCK(object);
 847                         for (j = i; j < runend; j++) {
 848                                 vm_page_lock(m[j]);
 849                                 vm_page_free(m[j]);
 850                                 vm_page_unlock(m[j]);
 851                         }
 852                         VM_OBJECT_UNLOCK(object);
 853                 } else {
 854                         if (runpg < (count - first)) {
 855                                 VM_OBJECT_LOCK(object);
 856                                 for (i = first + runpg; i < count; i++) {
 857                                         vm_page_lock(m[i]);
 858                                         vm_page_free(m[i]);
 859                                         vm_page_unlock(m[i]);
 860                                 }
 861                                 VM_OBJECT_UNLOCK(object);
 862                                 count = first + runpg;
 863                         }
 864                         break;
 865                 }
 866                 first = runend;
 867         }
 868
 869         /*
 870          * the first and last page have been calculated now, move input pages
 871          * to be zero based...
 872          */
 873         if (first != 0) {
 874                 m += first;
 875                 count -= first;
 876                 reqpage -= first;
 877         }
 878
 879         /*
 880          * calculate the file virtual address for the transfer
 881          */
 882         foff = IDX_TO_OFF(m[0]->pindex);
 883
 884         /*
 885          * calculate the size of the transfer
 886          */
 887         size = count * PAGE_SIZE;
 888         KASSERT(count > 0, ("zero count"));
 889         if ((foff + size) > object->un_pager.vnp.vnp_size)
 890                 size = object->un_pager.vnp.vnp_size - foff;
 891         KASSERT(size > 0, ("zero size"));
 892
 893         /*
 894          * round up physical size for real devices.
 895          */
 896         if (1) {
 897                 int secmask = bo->bo_bsize - 1;
 898                 KASSERT(secmask < PAGE_SIZE && secmask > 0,
 899                     ("vnode_pager_generic_getpages: sector size %d too large",
 900                     secmask + 1));
 901                 size = (size + secmask) & ~secmask;
 902         }
 903
 904         bp = getpbuf(&vnode_pbuf_freecnt);
 905         kva = (vm_offset_t) bp->b_data;
 906
 907         /*
 908          * and map the pages to be read into the kva
 909          */
 910         pmap_qenter(kva, m, count);
 911
 912         /* build a minimal buffer header */
 913         bp->b_iocmd = BIO_READ;
 914         bp->b_iodone = bdone;
 915         KASSERT(bp->b_rcred == NOCRED, ("leaking read ucred"));
 916         KASSERT(bp->b_wcred == NOCRED, ("leaking write ucred"));
 917         bp->b_rcred = crhold(curthread->td_ucred);
 918         bp->b_wcred = crhold(curthread->td_ucred);
 919         bp->b_blkno = firstaddr;
 920         pbgetbo(bo, bp);
 921         bp->b_vp = vp;
 922         bp->b_bcount = size;
 923         bp->b_bufsize = size;
 924         bp->b_runningbufspace = bp->b_bufsize;
 925         atomic_add_long(&runningbufspace, bp->b_runningbufspace);
 926
 927         PCPU_INC(cnt.v_vnodein);
 928         PCPU_ADD(cnt.v_vnodepgsin, count);
 929
 930         /* do the input */
 931         bp->b_iooffset = dbtob(bp->b_blkno);
 932         bstrategy(bp);
 933
 934         bwait(bp, PVM, "vnread");
 935
 936         if ((bp->b_ioflags & BIO_ERROR) != 0)
 937                 error = EIO;
 938
 939         if (!error) {
 940                 if (size != count * PAGE_SIZE)
 941                         bzero((caddr_t) kva + size, PAGE_SIZE * count - size);
 942         }
 943         pmap_qremove(kva, count);
 944
 945         /*
 946          * free the buffer header back to the swap buffer pool
 947          */
 948         bp->b_vp = NULL;
 949         pbrelbo(bp);
 950         relpbuf(bp, &vnode_pbuf_freecnt);
 951
 952         VM_OBJECT_LOCK(object);
 953         for (i = 0, tfoff = foff; i < count; i++, tfoff = nextoff) {
 954                 vm_page_t mt;
 955
 956                 nextoff = tfoff + PAGE_SIZE;
 957                 mt = m[i];
 958
 959                 if (nextoff <= object->un_pager.vnp.vnp_size) {
 960                         /*
 961                          * Read filled up entire page.
 962                          */
 963                         mt->valid = VM_PAGE_BITS_ALL;
 964                         KASSERT(mt->dirty == 0,
 965                             ("vnode_pager_generic_getpages: page %p is dirty",
 966                             mt));
 967                         KASSERT(!pmap_page_is_mapped(mt),
 968                             ("vnode_pager_generic_getpages: page %p is mapped",
 969                             mt));
 970                 } else {
 971                         /*
 972                          * Read did not fill up entire page.
 973                          *
 974                          * Currently we do not set the entire page valid,
 975                          * we just try to clear the piece that we couldn't
 976                          * read.
 977                          */
 978                         vm_page_set_valid(mt, 0,
 979                             object->un_pager.vnp.vnp_size - tfoff);
 980                         KASSERT((mt->dirty & vm_page_bits(0,
 981                             object->un_pager.vnp.vnp_size - tfoff)) == 0,
 982                             ("vnode_pager_generic_getpages: page %p is dirty",
 983                             mt));
 984                 }
 985
 986                 if (i != reqpage) {
 987
 988                         /*
 989                          * whether or not to leave the page activated is up in
 990                          * the air, but we should put the page on a page queue
 991                          * somewhere. (it already is in the object). Result:
 992                          * It appears that empirical results show that
 993                          * deactivating pages is best.
 994                          */
 995
 996                         /*
 997                          * just in case someone was asking for this page we
 998                          * now tell them that it is ok to use
 999                          */
1000                         if (!error) {
1001                                 if (mt->oflags & VPO_WANTED) {
1002                                         vm_page_lock(mt);
1003                                         vm_page_activate(mt);
1004                                         vm_page_unlock(mt);
1005                                 } else {
1006                                         vm_page_lock(mt);
1007                                         vm_page_deactivate(mt);
1008                                         vm_page_unlock(mt);
1009                                 }
1010                                 vm_page_wakeup(mt);
1011                         } else {
1012                                 vm_page_lock(mt);
1013                                 vm_page_free(mt);
1014                                 vm_page_unlock(mt);
1015                         }
1016                 }
1017         }
1018         VM_OBJECT_UNLOCK(object);
1019         if (error) {
1020                 printf("vnode_pager_getpages: I/O read error\n");
1021         }
1022         return (error ? VM_PAGER_ERROR : VM_PAGER_OK);
1023 }
1024
1025 /*
1026  * EOPNOTSUPP is no longer legal.  For local media VFS's that do not
1027  * implement their own VOP_PUTPAGES, their VOP_PUTPAGES should call to
1028  * vnode_pager_generic_putpages() to implement the previous behaviour.
1029  *
1030  * All other FS's should use the bypass to get to the local media
1031  * backing vp's VOP_PUTPAGES.
1032  */
1033 static void
1034 vnode_pager_putpages(object, m, count, sync, rtvals)
1035         vm_object_t object;
1036         vm_page_t *m;
1037         int count;
1038         boolean_t sync;
1039         int *rtvals;
1040 {
1041         int rtval;
1042         struct vnode *vp;
1043         int bytes = count * PAGE_SIZE;
1044
1045         /*
1046          * Force synchronous operation if we are extremely low on memory
1047          * to prevent a low-memory deadlock.  VOP operations often need to
1048          * allocate more memory to initiate the I/O ( i.e. do a BMAP
1049          * operation ).  The swapper handles the case by limiting the amount
1050          * of asynchronous I/O, but that sort of solution doesn't scale well
1051          * for the vnode pager without a lot of work.
1052          *
1053          * Also, the backing vnode's iodone routine may not wake the pageout
1054          * daemon up.  This should be probably be addressed XXX.
1055          */
1056
1057         if ((cnt.v_free_count + cnt.v_cache_count) < cnt.v_pageout_free_min)
1058                 sync |= OBJPC_SYNC;
1059
1060         /*
1061          * Call device-specific putpages function
1062          */
1063         vp = object->handle;
1064         VM_OBJECT_UNLOCK(object);
1065         rtval = VOP_PUTPAGES(vp, m, bytes, sync, rtvals, 0);
1066         KASSERT(rtval != EOPNOTSUPP,
1067             ("vnode_pager: stale FS putpages\n"));
1068         VM_OBJECT_LOCK(object);
1069 }
1070
1071
1072 /*
1073  * This is now called from local media FS's to operate against their
1074  * own vnodes if they fail to implement VOP_PUTPAGES.
1075  *
1076  * This is typically called indirectly via the pageout daemon and
1077  * clustering has already typically occured, so in general we ask the
1078  * underlying filesystem to write the data out asynchronously rather
1079  * then delayed.
1080  */
1081 int
1082 vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *ma, int bytecount,
1083     int flags, int *rtvals)
1084 {
1085         int i;
1086         vm_object_t object;
1087         vm_page_t m;
1088         int count;
1089
1090         int maxsize, ncount;
1091         vm_ooffset_t poffset;
1092         struct uio auio;
1093         struct iovec aiov;
1094         int error;
1095         int ioflags;
1096         int ppscheck = 0;
1097         static struct timeval lastfail;
1098         static int curfail;
1099
1100         object = vp->v_object;
1101         count = bytecount / PAGE_SIZE;
1102
1103         for (i = 0; i < count; i++)
1104                 rtvals[i] = VM_PAGER_ERROR;
1105
1106         if ((int64_t)ma[0]->pindex < 0) {
1107                 printf("vnode_pager_putpages: attempt to write meta-data!!! -- 0x%lx(%lx)\n",
1108                     (long)ma[0]->pindex, (u_long)ma[0]->dirty);
1109                 rtvals[0] = VM_PAGER_BAD;
1110                 return VM_PAGER_BAD;
1111         }
1112
1113         maxsize = count * PAGE_SIZE;
1114         ncount = count;
1115
1116         poffset = IDX_TO_OFF(ma[0]->pindex);
1117
1118         /*
1119          * If the page-aligned write is larger then the actual file we
1120          * have to invalidate pages occuring beyond the file EOF.  However,
1121          * there is an edge case where a file may not be page-aligned where
1122          * the last page is partially invalid.  In this case the filesystem
1123          * may not properly clear the dirty bits for the entire page (which
1124          * could be VM_PAGE_BITS_ALL due to the page having been mmap()d).
1125          * With the page locked we are free to fix-up the dirty bits here.
1126          *
1127          * We do not under any circumstances truncate the valid bits, as
1128          * this will screw up bogus page replacement.
1129          */
1130         VM_OBJECT_LOCK(object);
1131         if (maxsize + poffset > object->un_pager.vnp.vnp_size) {
1132                 if (object->un_pager.vnp.vnp_size > poffset) {
1133                         int pgoff;
1134
1135                         maxsize = object->un_pager.vnp.vnp_size - poffset;
1136                         ncount = btoc(maxsize);
1137                         if ((pgoff = (int)maxsize & PAGE_MASK) != 0) {
1138                                 /*
1139                                  * If the object is locked and the following
1140                                  * conditions hold, then the page's dirty
1141                                  * field cannot be concurrently changed by a
1142                                  * pmap operation.
1143                                  */
1144                                 m = ma[ncount - 1];
1145                                 KASSERT(m->busy > 0,
1146                 ("vnode_pager_generic_putpages: page %p is not busy", m));
1147                                 KASSERT((m->aflags & PGA_WRITEABLE) == 0,
1148                 ("vnode_pager_generic_putpages: page %p is not read-only", m));
1149                                 vm_page_clear_dirty(m, pgoff, PAGE_SIZE -
1150                                     pgoff);
1151                         }
1152                 } else {
1153                         maxsize = 0;
1154                         ncount = 0;
1155                 }
1156                 if (ncount < count) {
1157                         for (i = ncount; i < count; i++) {
1158                                 rtvals[i] = VM_PAGER_BAD;
1159                         }
1160                 }
1161         }
1162         VM_OBJECT_UNLOCK(object);
1163
1164         /*
1165          * pageouts are already clustered, use IO_ASYNC t o force a bawrite()
1166          * rather then a bdwrite() to prevent paging I/O from saturating
1167          * the buffer cache.  Dummy-up the sequential heuristic to cause
1168          * large ranges to cluster.  If neither IO_SYNC or IO_ASYNC is set,
1169          * the system decides how to cluster.
1170          */
1171         ioflags = IO_VMIO;
1172         if (flags & (VM_PAGER_PUT_SYNC | VM_PAGER_PUT_INVAL))
1173                 ioflags |= IO_SYNC;
1174         else if ((flags & VM_PAGER_CLUSTER_OK) == 0)
1175                 ioflags |= IO_ASYNC;
1176         ioflags |= (flags & VM_PAGER_PUT_INVAL) ? IO_INVAL: 0;
1177         ioflags |= IO_SEQMAX << IO_SEQSHIFT;
1178
1179         aiov.iov_base = (caddr_t) 0;
1180         aiov.iov_len = maxsize;
1181         auio.uio_iov = &aiov;
1182         auio.uio_iovcnt = 1;
1183         auio.uio_offset = poffset;
1184         auio.uio_segflg = UIO_NOCOPY;
1185         auio.uio_rw = UIO_WRITE;
1186         auio.uio_resid = maxsize;
1187         auio.uio_td = (struct thread *) 0;
1188         error = VOP_WRITE(vp, &auio, ioflags, curthread->td_ucred);
1189         PCPU_INC(cnt.v_vnodeout);
1190         PCPU_ADD(cnt.v_vnodepgsout, ncount);
1191
1192         if (error) {
1193                 if ((ppscheck = ppsratecheck(&lastfail, &curfail, 1)))
1194                         printf("vnode_pager_putpages: I/O error %d\n", error);
1195         }
1196         if (auio.uio_resid) {
1197                 if (ppscheck || ppsratecheck(&lastfail, &curfail, 1))
1198                         printf("vnode_pager_putpages: residual I/O %zd at %lu\n",
1199                             auio.uio_resid, (u_long)ma[0]->pindex);
1200         }
1201         for (i = 0; i < ncount; i++) {
1202                 rtvals[i] = VM_PAGER_OK;
1203         }
1204         return rtvals[0];
1205 }
1206
1207 void
1208 vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
1209 {
1210         vm_object_t obj;
1211         int i, pos;
1212
1213         if (written == 0)
1214                 return;
1215         obj = ma[0]->object;
1216         VM_OBJECT_LOCK(obj);
1217         for (i = 0, pos = 0; pos < written; i++, pos += PAGE_SIZE) {
1218                 if (pos < trunc_page(written)) {
1219                         rtvals[i] = VM_PAGER_OK;
1220                         vm_page_undirty(ma[i]);
1221                 } else {
1222                         /* Partially written page. */
1223                         rtvals[i] = VM_PAGER_AGAIN;
1224                         vm_page_clear_dirty(ma[i], 0, written & PAGE_MASK);
1225                 }
1226         }
1227         VM_OBJECT_UNLOCK(obj);
1228 }
1229
1230 void
1231 vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
1232     vm_offset_t end)
1233 {
1234         struct vnode *vp;
1235         vm_ooffset_t old_wm;
1236
1237         VM_OBJECT_LOCK(object);
1238         if (object->type != OBJT_VNODE) {
1239                 VM_OBJECT_UNLOCK(object);
1240                 return;
1241         }
1242         old_wm = object->un_pager.vnp.writemappings;
1243         object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
1244         vp = object->handle;
1245         if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
1246                 ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
1247                 vp->v_writecount++;
1248         } else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
1249                 ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
1250                 vp->v_writecount--;
1251         }
1252         VM_OBJECT_UNLOCK(object);
1253 }
1254
1255 void
1256 vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
1257     vm_offset_t end)
1258 {
1259         struct vnode *vp;
1260         struct mount *mp;
1261         vm_offset_t inc;
1262         int vfslocked;
1263
1264         VM_OBJECT_LOCK(object);
1265
1266         /*
1267          * First, recheck the object type to account for the race when
1268          * the vnode is reclaimed.
1269          */
1270         if (object->type != OBJT_VNODE) {
1271                 VM_OBJECT_UNLOCK(object);
1272                 return;
1273         }
1274
1275         /*
1276          * Optimize for the case when writemappings is not going to
1277          * zero.
1278          */
1279         inc = end - start;
1280         if (object->un_pager.vnp.writemappings != inc) {
1281                 object->un_pager.vnp.writemappings -= inc;
1282                 VM_OBJECT_UNLOCK(object);
1283                 return;
1284         }
1285
1286         vp = object->handle;
1287         vhold(vp);
1288         VM_OBJECT_UNLOCK(object);
1289         vfslocked = VFS_LOCK_GIANT(vp->v_mount);
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         VFS_UNLOCK_GIANT(vfslocked);
1306 }