The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_cluster.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  * Modifications/enhancements:
    7  *      Copyright (c) 1995 John S. Dyson.  All rights reserved.
    8  *
    9  * Redistribution and use in source and binary forms, with or without
   10  * modification, are permitted provided that the following conditions
   11  * are met:
   12  * 1. Redistributions of source code must retain the above copyright
   13  *    notice, this list of conditions and the following disclaimer.
   14  * 2. Redistributions in binary form must reproduce the above copyright
   15  *    notice, this list of conditions and the following disclaimer in the
   16  *    documentation and/or other materials provided with the distribution.
   17  * 3. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  *      @(#)vfs_cluster.c       8.7 (Berkeley) 2/13/94
   34  */
   35 
   36 #include <sys/cdefs.h>
   37 __FBSDID("$FreeBSD$");
   38 
   39 #include "opt_debug_cluster.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 #include <sys/kernel.h>
   44 #include <sys/proc.h>
   45 #include <sys/bio.h>
   46 #include <sys/buf.h>
   47 #include <sys/vnode.h>
   48 #include <sys/malloc.h>
   49 #include <sys/mount.h>
   50 #include <sys/racct.h>
   51 #include <sys/resourcevar.h>
   52 #include <sys/rwlock.h>
   53 #include <sys/vmmeter.h>
   54 #include <vm/vm.h>
   55 #include <vm/vm_object.h>
   56 #include <vm/vm_page.h>
   57 #include <sys/sysctl.h>
   58 
   59 #if defined(CLUSTERDEBUG)
   60 static int      rcluster= 0;
   61 SYSCTL_INT(_debug, OID_AUTO, rcluster, CTLFLAG_RW, &rcluster, 0,
   62     "Debug VFS clustering code");
   63 #endif
   64 
   65 static MALLOC_DEFINE(M_SEGMENT, "cl_savebuf", "cluster_save buffer");
   66 
   67 static struct cluster_save *cluster_collectbufs(struct vnode *vp,
   68             struct buf *last_bp, int gbflags);
   69 static struct buf *cluster_rbuild(struct vnode *vp, u_quad_t filesize,
   70             daddr_t lbn, daddr_t blkno, long size, int run, int gbflags,
   71             struct buf *fbp);
   72 static void cluster_callback(struct buf *);
   73 
   74 static int write_behind = 1;
   75 SYSCTL_INT(_vfs, OID_AUTO, write_behind, CTLFLAG_RW, &write_behind, 0,
   76     "Cluster write-behind; 0: disable, 1: enable, 2: backed off");
   77 
   78 static int read_max = 64;
   79 SYSCTL_INT(_vfs, OID_AUTO, read_max, CTLFLAG_RW, &read_max, 0,
   80     "Cluster read-ahead max block count");
   81 
   82 static int read_min = 1;
   83 SYSCTL_INT(_vfs, OID_AUTO, read_min, CTLFLAG_RW, &read_min, 0,
   84     "Cluster read min block count");
   85 
   86 /*
   87  * Read data to a buf, including read-ahead if we find this to be beneficial.
   88  * cluster_read replaces bread.
   89  */
   90 int
   91 cluster_read(struct vnode *vp, u_quad_t filesize, daddr_t lblkno, long size,
   92     struct ucred *cred, long totread, int seqcount, int gbflags,
   93     struct buf **bpp)
   94 {
   95         struct buf *bp, *rbp, *reqbp;
   96         struct bufobj *bo;
   97         struct thread *td;
   98         daddr_t blkno, origblkno;
   99         int maxra, racluster;
  100         int error, ncontig;
  101         int i;
  102 
  103         error = 0;
  104         td = curthread;
  105         bo = &vp->v_bufobj;
  106         if (!unmapped_buf_allowed)
  107                 gbflags &= ~GB_UNMAPPED;
  108 
  109         /*
  110          * Try to limit the amount of read-ahead by a few
  111          * ad-hoc parameters.  This needs work!!!
  112          */
  113         racluster = vp->v_mount->mnt_iosize_max / size;
  114         maxra = seqcount;
  115         maxra = min(read_max, maxra);
  116         maxra = min(nbuf/8, maxra);
  117         if (((u_quad_t)(lblkno + maxra + 1) * size) > filesize)
  118                 maxra = (filesize / size) - lblkno;
  119 
  120         /*
  121          * get the requested block
  122          */
  123         error = getblkx(vp, lblkno, size, 0, 0, gbflags, &bp);
  124         if (error != 0) {
  125                 *bpp = NULL;
  126                 return (error);
  127         }
  128         gbflags &= ~GB_NOSPARSE;
  129         origblkno = lblkno;
  130         *bpp = reqbp = bp;
  131 
  132         /*
  133          * if it is in the cache, then check to see if the reads have been
  134          * sequential.  If they have, then try some read-ahead, otherwise
  135          * back-off on prospective read-aheads.
  136          */
  137         if (bp->b_flags & B_CACHE) {
  138                 if (!seqcount) {
  139                         return 0;
  140                 } else if ((bp->b_flags & B_RAM) == 0) {
  141                         return 0;
  142                 } else {
  143                         bp->b_flags &= ~B_RAM;
  144                         BO_RLOCK(bo);
  145                         for (i = 1; i < maxra; i++) {
  146                                 /*
  147                                  * Stop if the buffer does not exist or it
  148                                  * is invalid (about to go away?)
  149                                  */
  150                                 rbp = gbincore(&vp->v_bufobj, lblkno+i);
  151                                 if (rbp == NULL || (rbp->b_flags & B_INVAL))
  152                                         break;
  153 
  154                                 /*
  155                                  * Set another read-ahead mark so we know 
  156                                  * to check again. (If we can lock the
  157                                  * buffer without waiting)
  158                                  */
  159                                 if ((((i % racluster) == (racluster - 1)) ||
  160                                     (i == (maxra - 1))) 
  161                                     && (0 == BUF_LOCK(rbp, 
  162                                         LK_EXCLUSIVE | LK_NOWAIT, NULL))) {
  163                                         rbp->b_flags |= B_RAM;
  164                                         BUF_UNLOCK(rbp);
  165                                 }                       
  166                         }
  167                         BO_RUNLOCK(bo);
  168                         if (i >= maxra) {
  169                                 return 0;
  170                         }
  171                         lblkno += i;
  172                 }
  173                 reqbp = bp = NULL;
  174         /*
  175          * If it isn't in the cache, then get a chunk from
  176          * disk if sequential, otherwise just get the block.
  177          */
  178         } else {
  179                 off_t firstread = bp->b_offset;
  180                 int nblks;
  181                 long minread;
  182 
  183                 KASSERT(bp->b_offset != NOOFFSET,
  184                     ("cluster_read: no buffer offset"));
  185 
  186                 ncontig = 0;
  187 
  188                 /*
  189                  * Adjust totread if needed
  190                  */
  191                 minread = read_min * size;
  192                 if (minread > totread)
  193                         totread = minread;
  194 
  195                 /*
  196                  * Compute the total number of blocks that we should read
  197                  * synchronously.
  198                  */
  199                 if (firstread + totread > filesize)
  200                         totread = filesize - firstread;
  201                 nblks = howmany(totread, size);
  202                 if (nblks > racluster)
  203                         nblks = racluster;
  204 
  205                 /*
  206                  * Now compute the number of contiguous blocks.
  207                  */
  208                 if (nblks > 1) {
  209                         error = VOP_BMAP(vp, lblkno, NULL,
  210                                 &blkno, &ncontig, NULL);
  211                         /*
  212                          * If this failed to map just do the original block.
  213                          */
  214                         if (error || blkno == -1)
  215                                 ncontig = 0;
  216                 }
  217 
  218                 /*
  219                  * If we have contiguous data available do a cluster
  220                  * otherwise just read the requested block.
  221                  */
  222                 if (ncontig) {
  223                         /* Account for our first block. */
  224                         ncontig = min(ncontig + 1, nblks);
  225                         if (ncontig < nblks)
  226                                 nblks = ncontig;
  227                         bp = cluster_rbuild(vp, filesize, lblkno,
  228                             blkno, size, nblks, gbflags, bp);
  229                         lblkno += (bp->b_bufsize / size);
  230                 } else {
  231                         bp->b_flags |= B_RAM;
  232                         bp->b_iocmd = BIO_READ;
  233                         lblkno += 1;
  234                 }
  235         }
  236 
  237         /*
  238          * handle the synchronous read so that it is available ASAP.
  239          */
  240         if (bp) {
  241                 if ((bp->b_flags & B_CLUSTER) == 0) {
  242                         vfs_busy_pages(bp, 0);
  243                 }
  244                 bp->b_flags &= ~B_INVAL;
  245                 bp->b_ioflags &= ~BIO_ERROR;
  246                 if ((bp->b_flags & B_ASYNC) || bp->b_iodone != NULL)
  247                         BUF_KERNPROC(bp);
  248                 bp->b_iooffset = dbtob(bp->b_blkno);
  249                 bstrategy(bp);
  250 #ifdef RACCT
  251                 if (racct_enable) {
  252                         PROC_LOCK(td->td_proc);
  253                         racct_add_buf(td->td_proc, bp, 0);
  254                         PROC_UNLOCK(td->td_proc);
  255                 }
  256 #endif /* RACCT */
  257                 td->td_ru.ru_inblock++;
  258         }
  259 
  260         /*
  261          * If we have been doing sequential I/O, then do some read-ahead.
  262          */
  263         while (lblkno < (origblkno + maxra)) {
  264                 error = VOP_BMAP(vp, lblkno, NULL, &blkno, &ncontig, NULL);
  265                 if (error)
  266                         break;
  267 
  268                 if (blkno == -1)
  269                         break;
  270 
  271                 /*
  272                  * We could throttle ncontig here by maxra but we might as
  273                  * well read the data if it is contiguous.  We're throttled
  274                  * by racluster anyway.
  275                  */
  276                 if (ncontig) {
  277                         ncontig = min(ncontig + 1, racluster);
  278                         rbp = cluster_rbuild(vp, filesize, lblkno, blkno,
  279                             size, ncontig, gbflags, NULL);
  280                         lblkno += (rbp->b_bufsize / size);
  281                         if (rbp->b_flags & B_DELWRI) {
  282                                 bqrelse(rbp);
  283                                 continue;
  284                         }
  285                 } else {
  286                         rbp = getblk(vp, lblkno, size, 0, 0, gbflags);
  287                         lblkno += 1;
  288                         if (rbp->b_flags & B_DELWRI) {
  289                                 bqrelse(rbp);
  290                                 continue;
  291                         }
  292                         rbp->b_flags |= B_ASYNC | B_RAM;
  293                         rbp->b_iocmd = BIO_READ;
  294                         rbp->b_blkno = blkno;
  295                 }
  296                 if (rbp->b_flags & B_CACHE) {
  297                         rbp->b_flags &= ~B_ASYNC;
  298                         bqrelse(rbp);
  299                         continue;
  300                 }
  301                 if ((rbp->b_flags & B_CLUSTER) == 0) {
  302                         vfs_busy_pages(rbp, 0);
  303                 }
  304                 rbp->b_flags &= ~B_INVAL;
  305                 rbp->b_ioflags &= ~BIO_ERROR;
  306                 if ((rbp->b_flags & B_ASYNC) || rbp->b_iodone != NULL)
  307                         BUF_KERNPROC(rbp);
  308                 rbp->b_iooffset = dbtob(rbp->b_blkno);
  309                 bstrategy(rbp);
  310 #ifdef RACCT
  311                 if (racct_enable) {
  312                         PROC_LOCK(td->td_proc);
  313                         racct_add_buf(td->td_proc, rbp, 0);
  314                         PROC_UNLOCK(td->td_proc);
  315                 }
  316 #endif /* RACCT */
  317                 td->td_ru.ru_inblock++;
  318         }
  319 
  320         if (reqbp) {
  321                 /*
  322                  * Like bread, always brelse() the buffer when
  323                  * returning an error.
  324                  */
  325                 error = bufwait(reqbp);
  326                 if (error != 0) {
  327                         brelse(reqbp);
  328                         *bpp = NULL;
  329                 }
  330         }
  331         return (error);
  332 }
  333 
  334 /*
  335  * If blocks are contiguous on disk, use this to provide clustered
  336  * read ahead.  We will read as many blocks as possible sequentially
  337  * and then parcel them up into logical blocks in the buffer hash table.
  338  */
  339 static struct buf *
  340 cluster_rbuild(struct vnode *vp, u_quad_t filesize, daddr_t lbn,
  341     daddr_t blkno, long size, int run, int gbflags, struct buf *fbp)
  342 {
  343         struct buf *bp, *tbp;
  344         daddr_t bn;
  345         off_t off;
  346         long tinc, tsize;
  347         int i, inc, j, k, toff;
  348 
  349         KASSERT(size == vp->v_mount->mnt_stat.f_iosize,
  350             ("cluster_rbuild: size %ld != f_iosize %jd\n",
  351             size, (intmax_t)vp->v_mount->mnt_stat.f_iosize));
  352 
  353         /*
  354          * avoid a division
  355          */
  356         while ((u_quad_t) size * (lbn + run) > filesize) {
  357                 --run;
  358         }
  359 
  360         if (fbp) {
  361                 tbp = fbp;
  362                 tbp->b_iocmd = BIO_READ; 
  363         } else {
  364                 tbp = getblk(vp, lbn, size, 0, 0, gbflags);
  365                 if (tbp->b_flags & B_CACHE)
  366                         return tbp;
  367                 tbp->b_flags |= B_ASYNC | B_RAM;
  368                 tbp->b_iocmd = BIO_READ;
  369         }
  370         tbp->b_blkno = blkno;
  371         if( (tbp->b_flags & B_MALLOC) ||
  372                 ((tbp->b_flags & B_VMIO) == 0) || (run <= 1) )
  373                 return tbp;
  374 
  375         bp = trypbuf(&cluster_pbuf_freecnt);
  376         if (bp == NULL)
  377                 return tbp;
  378 
  379         /*
  380          * We are synthesizing a buffer out of vm_page_t's, but
  381          * if the block size is not page aligned then the starting
  382          * address may not be either.  Inherit the b_data offset
  383          * from the original buffer.
  384          */
  385         bp->b_flags = B_ASYNC | B_CLUSTER | B_VMIO;
  386         if ((gbflags & GB_UNMAPPED) != 0) {
  387                 bp->b_data = unmapped_buf;
  388         } else {
  389                 bp->b_data = (char *)((vm_offset_t)bp->b_data |
  390                     ((vm_offset_t)tbp->b_data & PAGE_MASK));
  391         }
  392         bp->b_iocmd = BIO_READ;
  393         bp->b_iodone = cluster_callback;
  394         bp->b_blkno = blkno;
  395         bp->b_lblkno = lbn;
  396         bp->b_offset = tbp->b_offset;
  397         KASSERT(bp->b_offset != NOOFFSET, ("cluster_rbuild: no buffer offset"));
  398         pbgetvp(vp, bp);
  399 
  400         TAILQ_INIT(&bp->b_cluster.cluster_head);
  401 
  402         bp->b_bcount = 0;
  403         bp->b_bufsize = 0;
  404         bp->b_npages = 0;
  405 
  406         inc = btodb(size);
  407         for (bn = blkno, i = 0; i < run; ++i, bn += inc) {
  408                 if (i == 0) {
  409                         VM_OBJECT_WLOCK(tbp->b_bufobj->bo_object);
  410                         vfs_drain_busy_pages(tbp);
  411                         vm_object_pip_add(tbp->b_bufobj->bo_object,
  412                             tbp->b_npages);
  413                         for (k = 0; k < tbp->b_npages; k++)
  414                                 vm_page_sbusy(tbp->b_pages[k]);
  415                         VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
  416                 } else {
  417                         if ((bp->b_npages * PAGE_SIZE) +
  418                             round_page(size) > vp->v_mount->mnt_iosize_max) {
  419                                 break;
  420                         }
  421 
  422                         tbp = getblk(vp, lbn + i, size, 0, 0, GB_LOCK_NOWAIT |
  423                             (gbflags & GB_UNMAPPED));
  424 
  425                         /* Don't wait around for locked bufs. */
  426                         if (tbp == NULL)
  427                                 break;
  428 
  429                         /*
  430                          * Stop scanning if the buffer is fully valid
  431                          * (marked B_CACHE), or locked (may be doing a
  432                          * background write), or if the buffer is not
  433                          * VMIO backed.  The clustering code can only deal
  434                          * with VMIO-backed buffers.  The bo lock is not
  435                          * required for the BKGRDINPROG check since it
  436                          * can not be set without the buf lock.
  437                          */
  438                         if ((tbp->b_vflags & BV_BKGRDINPROG) ||
  439                             (tbp->b_flags & B_CACHE) ||
  440                             (tbp->b_flags & B_VMIO) == 0) {
  441                                 bqrelse(tbp);
  442                                 break;
  443                         }
  444 
  445                         /*
  446                          * The buffer must be completely invalid in order to
  447                          * take part in the cluster.  If it is partially valid
  448                          * then we stop.
  449                          */
  450                         off = tbp->b_offset;
  451                         tsize = size;
  452                         VM_OBJECT_WLOCK(tbp->b_bufobj->bo_object);
  453                         for (j = 0; tsize > 0; j++) {
  454                                 toff = off & PAGE_MASK;
  455                                 tinc = tsize;
  456                                 if (toff + tinc > PAGE_SIZE)
  457                                         tinc = PAGE_SIZE - toff;
  458                                 VM_OBJECT_ASSERT_WLOCKED(tbp->b_pages[j]->object);
  459                                 if ((tbp->b_pages[j]->valid &
  460                                     vm_page_bits(toff, tinc)) != 0)
  461                                         break;
  462                                 if (vm_page_xbusied(tbp->b_pages[j]))
  463                                         break;
  464                                 vm_object_pip_add(tbp->b_bufobj->bo_object, 1);
  465                                 vm_page_sbusy(tbp->b_pages[j]);
  466                                 off += tinc;
  467                                 tsize -= tinc;
  468                         }
  469                         if (tsize > 0) {
  470 clean_sbusy:
  471                                 vm_object_pip_add(tbp->b_bufobj->bo_object, -j);
  472                                 for (k = 0; k < j; k++)
  473                                         vm_page_sunbusy(tbp->b_pages[k]);
  474                                 VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
  475                                 bqrelse(tbp);
  476                                 break;
  477                         }
  478                         VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
  479 
  480                         /*
  481                          * Set a read-ahead mark as appropriate
  482                          */
  483                         if ((fbp && (i == 1)) || (i == (run - 1)))
  484                                 tbp->b_flags |= B_RAM;
  485 
  486                         /*
  487                          * Set the buffer up for an async read (XXX should
  488                          * we do this only if we do not wind up brelse()ing?).
  489                          * Set the block number if it isn't set, otherwise
  490                          * if it is make sure it matches the block number we
  491                          * expect.
  492                          */
  493                         tbp->b_flags |= B_ASYNC;
  494                         tbp->b_iocmd = BIO_READ;
  495                         if (tbp->b_blkno == tbp->b_lblkno) {
  496                                 tbp->b_blkno = bn;
  497                         } else if (tbp->b_blkno != bn) {
  498                                 VM_OBJECT_WLOCK(tbp->b_bufobj->bo_object);
  499                                 goto clean_sbusy;
  500                         }
  501                 }
  502                 /*
  503                  * XXX fbp from caller may not be B_ASYNC, but we are going
  504                  * to biodone() it in cluster_callback() anyway
  505                  */
  506                 BUF_KERNPROC(tbp);
  507                 TAILQ_INSERT_TAIL(&bp->b_cluster.cluster_head,
  508                         tbp, b_cluster.cluster_entry);
  509                 VM_OBJECT_WLOCK(tbp->b_bufobj->bo_object);
  510                 for (j = 0; j < tbp->b_npages; j += 1) {
  511                         vm_page_t m;
  512                         m = tbp->b_pages[j];
  513                         if ((bp->b_npages == 0) ||
  514                             (bp->b_pages[bp->b_npages-1] != m)) {
  515                                 bp->b_pages[bp->b_npages] = m;
  516                                 bp->b_npages++;
  517                         }
  518                         if (m->valid == VM_PAGE_BITS_ALL)
  519                                 tbp->b_pages[j] = bogus_page;
  520                 }
  521                 VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
  522                 /*
  523                  * Don't inherit tbp->b_bufsize as it may be larger due to
  524                  * a non-page-aligned size.  Instead just aggregate using
  525                  * 'size'.
  526                  */
  527                 if (tbp->b_bcount != size)
  528                         printf("warning: tbp->b_bcount wrong %ld vs %ld\n", tbp->b_bcount, size);
  529                 if (tbp->b_bufsize != size)
  530                         printf("warning: tbp->b_bufsize wrong %ld vs %ld\n", tbp->b_bufsize, size);
  531                 bp->b_bcount += size;
  532                 bp->b_bufsize += size;
  533         }
  534 
  535         /*
  536          * Fully valid pages in the cluster are already good and do not need
  537          * to be re-read from disk.  Replace the page with bogus_page
  538          */
  539         VM_OBJECT_WLOCK(bp->b_bufobj->bo_object);
  540         for (j = 0; j < bp->b_npages; j++) {
  541                 VM_OBJECT_ASSERT_WLOCKED(bp->b_pages[j]->object);
  542                 if (bp->b_pages[j]->valid == VM_PAGE_BITS_ALL)
  543                         bp->b_pages[j] = bogus_page;
  544         }
  545         VM_OBJECT_WUNLOCK(bp->b_bufobj->bo_object);
  546         if (bp->b_bufsize > bp->b_kvasize)
  547                 panic("cluster_rbuild: b_bufsize(%ld) > b_kvasize(%d)\n",
  548                     bp->b_bufsize, bp->b_kvasize);
  549 
  550         if (buf_mapped(bp)) {
  551                 pmap_qenter(trunc_page((vm_offset_t) bp->b_data),
  552                     (vm_page_t *)bp->b_pages, bp->b_npages);
  553         }
  554         return (bp);
  555 }
  556 
  557 /*
  558  * Cleanup after a clustered read or write.
  559  * This is complicated by the fact that any of the buffers might have
  560  * extra memory (if there were no empty buffer headers at allocbuf time)
  561  * that we will need to shift around.
  562  */
  563 static void
  564 cluster_callback(struct buf *bp)
  565 {
  566         struct buf *nbp, *tbp;
  567         int error = 0;
  568 
  569         /*
  570          * Must propagate errors to all the components.
  571          */
  572         if (bp->b_ioflags & BIO_ERROR)
  573                 error = bp->b_error;
  574 
  575         if (buf_mapped(bp)) {
  576                 pmap_qremove(trunc_page((vm_offset_t) bp->b_data),
  577                     bp->b_npages);
  578         }
  579         /*
  580          * Move memory from the large cluster buffer into the component
  581          * buffers and mark IO as done on these.
  582          */
  583         for (tbp = TAILQ_FIRST(&bp->b_cluster.cluster_head);
  584                 tbp; tbp = nbp) {
  585                 nbp = TAILQ_NEXT(&tbp->b_cluster, cluster_entry);
  586                 if (error) {
  587                         tbp->b_ioflags |= BIO_ERROR;
  588                         tbp->b_error = error;
  589                 } else {
  590                         tbp->b_dirtyoff = tbp->b_dirtyend = 0;
  591                         tbp->b_flags &= ~B_INVAL;
  592                         tbp->b_ioflags &= ~BIO_ERROR;
  593                         /*
  594                          * XXX the bdwrite()/bqrelse() issued during
  595                          * cluster building clears B_RELBUF (see bqrelse()
  596                          * comment).  If direct I/O was specified, we have
  597                          * to restore it here to allow the buffer and VM
  598                          * to be freed.
  599                          */
  600                         if (tbp->b_flags & B_DIRECT)
  601                                 tbp->b_flags |= B_RELBUF;
  602                 }
  603                 bufdone(tbp);
  604         }
  605         pbrelvp(bp);
  606         relpbuf(bp, &cluster_pbuf_freecnt);
  607 }
  608 
  609 /*
  610  *      cluster_wbuild_wb:
  611  *
  612  *      Implement modified write build for cluster.
  613  *
  614  *              write_behind = 0        write behind disabled
  615  *              write_behind = 1        write behind normal (default)
  616  *              write_behind = 2        write behind backed-off
  617  */
  618 
  619 static __inline int
  620 cluster_wbuild_wb(struct vnode *vp, long size, daddr_t start_lbn, int len,
  621     int gbflags)
  622 {
  623         int r = 0;
  624 
  625         switch (write_behind) {
  626         case 2:
  627                 if (start_lbn < len)
  628                         break;
  629                 start_lbn -= len;
  630                 /* FALLTHROUGH */
  631         case 1:
  632                 r = cluster_wbuild(vp, size, start_lbn, len, gbflags);
  633                 /* FALLTHROUGH */
  634         default:
  635                 /* FALLTHROUGH */
  636                 break;
  637         }
  638         return(r);
  639 }
  640 
  641 /*
  642  * Do clustered write for FFS.
  643  *
  644  * Three cases:
  645  *      1. Write is not sequential (write asynchronously)
  646  *      Write is sequential:
  647  *      2.      beginning of cluster - begin cluster
  648  *      3.      middle of a cluster - add to cluster
  649  *      4.      end of a cluster - asynchronously write cluster
  650  */
  651 void
  652 cluster_write(struct vnode *vp, struct buf *bp, u_quad_t filesize, int seqcount,
  653     int gbflags)
  654 {
  655         daddr_t lbn;
  656         int maxclen, cursize;
  657         int lblocksize;
  658         int async;
  659 
  660         if (!unmapped_buf_allowed)
  661                 gbflags &= ~GB_UNMAPPED;
  662 
  663         if (vp->v_type == VREG) {
  664                 async = DOINGASYNC(vp);
  665                 lblocksize = vp->v_mount->mnt_stat.f_iosize;
  666         } else {
  667                 async = 0;
  668                 lblocksize = bp->b_bufsize;
  669         }
  670         lbn = bp->b_lblkno;
  671         KASSERT(bp->b_offset != NOOFFSET, ("cluster_write: no buffer offset"));
  672 
  673         /* Initialize vnode to beginning of file. */
  674         if (lbn == 0)
  675                 vp->v_lasta = vp->v_clen = vp->v_cstart = vp->v_lastw = 0;
  676 
  677         if (vp->v_clen == 0 || lbn != vp->v_lastw + 1 ||
  678             (bp->b_blkno != vp->v_lasta + btodb(lblocksize))) {
  679                 maxclen = vp->v_mount->mnt_iosize_max / lblocksize - 1;
  680                 if (vp->v_clen != 0) {
  681                         /*
  682                          * Next block is not sequential.
  683                          *
  684                          * If we are not writing at end of file, the process
  685                          * seeked to another point in the file since its last
  686                          * write, or we have reached our maximum cluster size,
  687                          * then push the previous cluster. Otherwise try
  688                          * reallocating to make it sequential.
  689                          *
  690                          * Change to algorithm: only push previous cluster if
  691                          * it was sequential from the point of view of the
  692                          * seqcount heuristic, otherwise leave the buffer 
  693                          * intact so we can potentially optimize the I/O
  694                          * later on in the buf_daemon or update daemon
  695                          * flush.
  696                          */
  697                         cursize = vp->v_lastw - vp->v_cstart + 1;
  698                         if (((u_quad_t) bp->b_offset + lblocksize) != filesize ||
  699                             lbn != vp->v_lastw + 1 || vp->v_clen <= cursize) {
  700                                 if (!async && seqcount > 0) {
  701                                         cluster_wbuild_wb(vp, lblocksize,
  702                                             vp->v_cstart, cursize, gbflags);
  703                                 }
  704                         } else {
  705                                 struct buf **bpp, **endbp;
  706                                 struct cluster_save *buflist;
  707 
  708                                 buflist = cluster_collectbufs(vp, bp, gbflags);
  709                                 if (buflist == NULL) {
  710                                         /*
  711                                          * Cluster build failed so just write
  712                                          * it now.
  713                                          */
  714                                         bawrite(bp);
  715                                         return;
  716                                 }
  717                                 endbp = &buflist->bs_children
  718                                     [buflist->bs_nchildren - 1];
  719                                 if (VOP_REALLOCBLKS(vp, buflist)) {
  720                                         /*
  721                                          * Failed, push the previous cluster
  722                                          * if *really* writing sequentially
  723                                          * in the logical file (seqcount > 1),
  724                                          * otherwise delay it in the hopes that
  725                                          * the low level disk driver can
  726                                          * optimize the write ordering.
  727                                          */
  728                                         for (bpp = buflist->bs_children;
  729                                              bpp < endbp; bpp++)
  730                                                 brelse(*bpp);
  731                                         free(buflist, M_SEGMENT);
  732                                         if (seqcount > 1) {
  733                                                 cluster_wbuild_wb(vp, 
  734                                                     lblocksize, vp->v_cstart, 
  735                                                     cursize, gbflags);
  736                                         }
  737                                 } else {
  738                                         /*
  739                                          * Succeeded, keep building cluster.
  740                                          */
  741                                         for (bpp = buflist->bs_children;
  742                                              bpp <= endbp; bpp++)
  743                                                 bdwrite(*bpp);
  744                                         free(buflist, M_SEGMENT);
  745                                         vp->v_lastw = lbn;
  746                                         vp->v_lasta = bp->b_blkno;
  747                                         return;
  748                                 }
  749                         }
  750                 }
  751                 /*
  752                  * Consider beginning a cluster. If at end of file, make
  753                  * cluster as large as possible, otherwise find size of
  754                  * existing cluster.
  755                  */
  756                 if ((vp->v_type == VREG) &&
  757                         ((u_quad_t) bp->b_offset + lblocksize) != filesize &&
  758                     (bp->b_blkno == bp->b_lblkno) &&
  759                     (VOP_BMAP(vp, lbn, NULL, &bp->b_blkno, &maxclen, NULL) ||
  760                      bp->b_blkno == -1)) {
  761                         bawrite(bp);
  762                         vp->v_clen = 0;
  763                         vp->v_lasta = bp->b_blkno;
  764                         vp->v_cstart = lbn + 1;
  765                         vp->v_lastw = lbn;
  766                         return;
  767                 }
  768                 vp->v_clen = maxclen;
  769                 if (!async && maxclen == 0) {   /* I/O not contiguous */
  770                         vp->v_cstart = lbn + 1;
  771                         bawrite(bp);
  772                 } else {        /* Wait for rest of cluster */
  773                         vp->v_cstart = lbn;
  774                         bdwrite(bp);
  775                 }
  776         } else if (lbn == vp->v_cstart + vp->v_clen) {
  777                 /*
  778                  * At end of cluster, write it out if seqcount tells us we
  779                  * are operating sequentially, otherwise let the buf or
  780                  * update daemon handle it.
  781                  */
  782                 bdwrite(bp);
  783                 if (seqcount > 1) {
  784                         cluster_wbuild_wb(vp, lblocksize, vp->v_cstart,
  785                             vp->v_clen + 1, gbflags);
  786                 }
  787                 vp->v_clen = 0;
  788                 vp->v_cstart = lbn + 1;
  789         } else if (vm_page_count_severe()) {
  790                 /*
  791                  * We are low on memory, get it going NOW
  792                  */
  793                 bawrite(bp);
  794         } else {
  795                 /*
  796                  * In the middle of a cluster, so just delay the I/O for now.
  797                  */
  798                 bdwrite(bp);
  799         }
  800         vp->v_lastw = lbn;
  801         vp->v_lasta = bp->b_blkno;
  802 }
  803 
  804 
  805 /*
  806  * This is an awful lot like cluster_rbuild...wish they could be combined.
  807  * The last lbn argument is the current block on which I/O is being
  808  * performed.  Check to see that it doesn't fall in the middle of
  809  * the current block (if last_bp == NULL).
  810  */
  811 int
  812 cluster_wbuild(struct vnode *vp, long size, daddr_t start_lbn, int len,
  813     int gbflags)
  814 {
  815         struct buf *bp, *tbp;
  816         struct bufobj *bo;
  817         int i, j;
  818         int totalwritten = 0;
  819         int dbsize = btodb(size);
  820 
  821         if (!unmapped_buf_allowed)
  822                 gbflags &= ~GB_UNMAPPED;
  823 
  824         bo = &vp->v_bufobj;
  825         while (len > 0) {
  826                 /*
  827                  * If the buffer is not delayed-write (i.e. dirty), or it
  828                  * is delayed-write but either locked or inval, it cannot
  829                  * partake in the clustered write.
  830                  */
  831                 BO_LOCK(bo);
  832                 if ((tbp = gbincore(&vp->v_bufobj, start_lbn)) == NULL ||
  833                     (tbp->b_vflags & BV_BKGRDINPROG)) {
  834                         BO_UNLOCK(bo);
  835                         ++start_lbn;
  836                         --len;
  837                         continue;
  838                 }
  839                 if (BUF_LOCK(tbp,
  840                     LK_EXCLUSIVE | LK_NOWAIT | LK_INTERLOCK, BO_LOCKPTR(bo))) {
  841                         ++start_lbn;
  842                         --len;
  843                         continue;
  844                 }
  845                 if ((tbp->b_flags & (B_INVAL | B_DELWRI)) != B_DELWRI) {
  846                         BUF_UNLOCK(tbp);
  847                         ++start_lbn;
  848                         --len;
  849                         continue;
  850                 }
  851                 bremfree(tbp);
  852                 tbp->b_flags &= ~B_DONE;
  853 
  854                 /*
  855                  * Extra memory in the buffer, punt on this buffer.
  856                  * XXX we could handle this in most cases, but we would
  857                  * have to push the extra memory down to after our max
  858                  * possible cluster size and then potentially pull it back
  859                  * up if the cluster was terminated prematurely--too much
  860                  * hassle.
  861                  */
  862                 if (((tbp->b_flags & (B_CLUSTEROK | B_MALLOC | B_VMIO)) != 
  863                      (B_CLUSTEROK | B_VMIO)) ||
  864                   (tbp->b_bcount != tbp->b_bufsize) ||
  865                   (tbp->b_bcount != size) ||
  866                   (len == 1) ||
  867                   ((bp = (vp->v_vflag & VV_MD) != 0 ?
  868                   trypbuf(&cluster_pbuf_freecnt) :
  869                   getpbuf(&cluster_pbuf_freecnt)) == NULL)) {
  870                         totalwritten += tbp->b_bufsize;
  871                         bawrite(tbp);
  872                         ++start_lbn;
  873                         --len;
  874                         continue;
  875                 }
  876 
  877                 /*
  878                  * We got a pbuf to make the cluster in.
  879                  * so initialise it.
  880                  */
  881                 TAILQ_INIT(&bp->b_cluster.cluster_head);
  882                 bp->b_bcount = 0;
  883                 bp->b_bufsize = 0;
  884                 bp->b_npages = 0;
  885                 if (tbp->b_wcred != NOCRED)
  886                         bp->b_wcred = crhold(tbp->b_wcred);
  887 
  888                 bp->b_blkno = tbp->b_blkno;
  889                 bp->b_lblkno = tbp->b_lblkno;
  890                 bp->b_offset = tbp->b_offset;
  891 
  892                 /*
  893                  * We are synthesizing a buffer out of vm_page_t's, but
  894                  * if the block size is not page aligned then the starting
  895                  * address may not be either.  Inherit the b_data offset
  896                  * from the original buffer.
  897                  */
  898                 if ((gbflags & GB_UNMAPPED) == 0 ||
  899                     (tbp->b_flags & B_VMIO) == 0) {
  900                         bp->b_data = (char *)((vm_offset_t)bp->b_data |
  901                             ((vm_offset_t)tbp->b_data & PAGE_MASK));
  902                 } else {
  903                         bp->b_data = unmapped_buf;
  904                 }
  905                 bp->b_flags |= B_CLUSTER | (tbp->b_flags & (B_VMIO |
  906                     B_NEEDCOMMIT));
  907                 bp->b_iodone = cluster_callback;
  908                 pbgetvp(vp, bp);
  909                 /*
  910                  * From this location in the file, scan forward to see
  911                  * if there are buffers with adjacent data that need to
  912                  * be written as well.
  913                  */
  914                 for (i = 0; i < len; ++i, ++start_lbn) {
  915                         if (i != 0) { /* If not the first buffer */
  916                                 /*
  917                                  * If the adjacent data is not even in core it
  918                                  * can't need to be written.
  919                                  */
  920                                 BO_LOCK(bo);
  921                                 if ((tbp = gbincore(bo, start_lbn)) == NULL ||
  922                                     (tbp->b_vflags & BV_BKGRDINPROG)) {
  923                                         BO_UNLOCK(bo);
  924                                         break;
  925                                 }
  926 
  927                                 /*
  928                                  * If it IS in core, but has different
  929                                  * characteristics, or is locked (which
  930                                  * means it could be undergoing a background
  931                                  * I/O or be in a weird state), then don't
  932                                  * cluster with it.
  933                                  */
  934                                 if (BUF_LOCK(tbp,
  935                                     LK_EXCLUSIVE | LK_NOWAIT | LK_INTERLOCK,
  936                                     BO_LOCKPTR(bo)))
  937                                         break;
  938 
  939                                 if ((tbp->b_flags & (B_VMIO | B_CLUSTEROK |
  940                                     B_INVAL | B_DELWRI | B_NEEDCOMMIT))
  941                                     != (B_DELWRI | B_CLUSTEROK |
  942                                     (bp->b_flags & (B_VMIO | B_NEEDCOMMIT))) ||
  943                                     tbp->b_wcred != bp->b_wcred) {
  944                                         BUF_UNLOCK(tbp);
  945                                         break;
  946                                 }
  947 
  948                                 /*
  949                                  * Check that the combined cluster
  950                                  * would make sense with regard to pages
  951                                  * and would not be too large
  952                                  */
  953                                 if ((tbp->b_bcount != size) ||
  954                                   ((bp->b_blkno + (dbsize * i)) !=
  955                                     tbp->b_blkno) ||
  956                                   ((tbp->b_npages + bp->b_npages) >
  957                                     (vp->v_mount->mnt_iosize_max / PAGE_SIZE))) {
  958                                         BUF_UNLOCK(tbp);
  959                                         break;
  960                                 }
  961 
  962                                 /*
  963                                  * Ok, it's passed all the tests,
  964                                  * so remove it from the free list
  965                                  * and mark it busy. We will use it.
  966                                  */
  967                                 bremfree(tbp);
  968                                 tbp->b_flags &= ~B_DONE;
  969                         } /* end of code for non-first buffers only */
  970                         /*
  971                          * If the IO is via the VM then we do some
  972                          * special VM hackery (yuck).  Since the buffer's
  973                          * block size may not be page-aligned it is possible
  974                          * for a page to be shared between two buffers.  We
  975                          * have to get rid of the duplication when building
  976                          * the cluster.
  977                          */
  978                         if (tbp->b_flags & B_VMIO) {
  979                                 vm_page_t m;
  980 
  981                                 VM_OBJECT_WLOCK(tbp->b_bufobj->bo_object);
  982                                 if (i == 0) {
  983                                         vfs_drain_busy_pages(tbp);
  984                                 } else { /* if not first buffer */
  985                                         for (j = 0; j < tbp->b_npages; j += 1) {
  986                                                 m = tbp->b_pages[j];
  987                                                 if (vm_page_xbusied(m)) {
  988                                                         VM_OBJECT_WUNLOCK(
  989                                                             tbp->b_object);
  990                                                         bqrelse(tbp);
  991                                                         goto finishcluster;
  992                                                 }
  993                                         }
  994                                 }
  995                                 for (j = 0; j < tbp->b_npages; j += 1) {
  996                                         m = tbp->b_pages[j];
  997                                         vm_page_sbusy(m);
  998                                         vm_object_pip_add(m->object, 1);
  999                                         if ((bp->b_npages == 0) ||
 1000                                           (bp->b_pages[bp->b_npages - 1] != m)) {
 1001                                                 bp->b_pages[bp->b_npages] = m;
 1002                                                 bp->b_npages++;
 1003                                         }
 1004                                 }
 1005                                 VM_OBJECT_WUNLOCK(tbp->b_bufobj->bo_object);
 1006                         }
 1007                         bp->b_bcount += size;
 1008                         bp->b_bufsize += size;
 1009                         /*
 1010                          * If any of the clustered buffers have their
 1011                          * B_BARRIER flag set, transfer that request to
 1012                          * the cluster.
 1013                          */
 1014                         bp->b_flags |= (tbp->b_flags & B_BARRIER);
 1015                         tbp->b_flags &= ~(B_DONE | B_BARRIER);
 1016                         tbp->b_flags |= B_ASYNC;
 1017                         tbp->b_ioflags &= ~BIO_ERROR;
 1018                         tbp->b_iocmd = BIO_WRITE;
 1019                         bundirty(tbp);
 1020                         reassignbuf(tbp);               /* put on clean list */
 1021                         bufobj_wref(tbp->b_bufobj);
 1022                         BUF_KERNPROC(tbp);
 1023                         buf_track(tbp, __func__);
 1024                         TAILQ_INSERT_TAIL(&bp->b_cluster.cluster_head,
 1025                                 tbp, b_cluster.cluster_entry);
 1026                 }
 1027         finishcluster:
 1028                 if (buf_mapped(bp)) {
 1029                         pmap_qenter(trunc_page((vm_offset_t) bp->b_data),
 1030                             (vm_page_t *)bp->b_pages, bp->b_npages);
 1031                 }
 1032                 if (bp->b_bufsize > bp->b_kvasize)
 1033                         panic(
 1034                             "cluster_wbuild: b_bufsize(%ld) > b_kvasize(%d)\n",
 1035                             bp->b_bufsize, bp->b_kvasize);
 1036                 totalwritten += bp->b_bufsize;
 1037                 bp->b_dirtyoff = 0;
 1038                 bp->b_dirtyend = bp->b_bufsize;
 1039                 bawrite(bp);
 1040 
 1041                 len -= i;
 1042         }
 1043         return totalwritten;
 1044 }
 1045 
 1046 /*
 1047  * Collect together all the buffers in a cluster.
 1048  * Plus add one additional buffer.
 1049  */
 1050 static struct cluster_save *
 1051 cluster_collectbufs(struct vnode *vp, struct buf *last_bp, int gbflags)
 1052 {
 1053         struct cluster_save *buflist;
 1054         struct buf *bp;
 1055         daddr_t lbn;
 1056         int i, j, len, error;
 1057 
 1058         len = vp->v_lastw - vp->v_cstart + 1;
 1059         buflist = malloc(sizeof(struct buf *) * (len + 1) + sizeof(*buflist),
 1060             M_SEGMENT, M_WAITOK);
 1061         buflist->bs_nchildren = 0;
 1062         buflist->bs_children = (struct buf **) (buflist + 1);
 1063         for (lbn = vp->v_cstart, i = 0; i < len; lbn++, i++) {
 1064                 error = bread_gb(vp, lbn, last_bp->b_bcount, NOCRED,
 1065                     gbflags, &bp);
 1066                 if (error != 0) {
 1067                         /*
 1068                          * If read fails, release collected buffers
 1069                          * and return failure.
 1070                          */
 1071                         for (j = 0; j < i; j++)
 1072                                 brelse(buflist->bs_children[j]);
 1073                         free(buflist, M_SEGMENT);
 1074                         return (NULL);
 1075                 }
 1076                 buflist->bs_children[i] = bp;
 1077                 if (bp->b_blkno == bp->b_lblkno)
 1078                         VOP_BMAP(vp, bp->b_lblkno, NULL, &bp->b_blkno,
 1079                                 NULL, NULL);
 1080         }
 1081         buflist->bs_children[i] = bp = last_bp;
 1082         if (bp->b_blkno == bp->b_lblkno)
 1083                 VOP_BMAP(vp, bp->b_lblkno, NULL, &bp->b_blkno, NULL, NULL);
 1084         buflist->bs_nchildren = i + 1;
 1085         return (buflist);
 1086 }

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