- Regularize variable usage in cluster_read().
- Issue the io that we will later block on prior to doing cluster read ahead so that it is more likely to be ready when we block. - Loop issuing clustered reads until we've exhausted the seq count supplied by the file system. - Use a sysctl tunable "vfs.read_max" to determine the maximum number of blocks that we'll read ahead.
This commit is contained in:
Jeff Roberson
parent
8685444543
commit
9ec559555b
@ -73,6 +73,10 @@ static int write_behind = 1;
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SYSCTL_INT(_vfs, OID_AUTO, write_behind, CTLFLAG_RW, &write_behind, 0,
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"Cluster write-behind; 0: disable, 1: enable, 2: backed off");
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static int read_max = 64;
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SYSCTL_INT(_vfs, OID_AUTO, read_max, CTLFLAG_RW, &read_max, 0,
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"Cluster read-ahead max block count");
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/* Page expended to mark partially backed buffers */
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extern vm_page_t bogus_page;
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@ -82,11 +86,6 @@ extern vm_page_t bogus_page;
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*/
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extern int cluster_pbuf_freecnt;
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/*
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* Maximum number of blocks for read-ahead.
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*/
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#define MAXRA 32
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/*
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* Read data to a buf, including read-ahead if we find this to be beneficial.
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* cluster_read replaces bread.
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@ -104,10 +103,9 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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{
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struct buf *bp, *rbp, *reqbp;
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daddr_t blkno, origblkno;
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int error, num_ra;
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int i;
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int maxra, racluster;
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long origtotread;
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int error, ncontig;
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int i;
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error = 0;
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@ -116,18 +114,17 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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* ad-hoc parameters. This needs work!!!
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*/
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racluster = vp->v_mount->mnt_iosize_max / size;
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maxra = 2 * racluster + (totread / size);
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if (maxra > MAXRA)
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maxra = MAXRA;
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if (maxra > nbuf/8)
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maxra = nbuf/8;
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maxra = seqcount;
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maxra = min(read_max, maxra);
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maxra = min(nbuf/8, maxra);
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if (((u_quad_t)(lblkno + maxra + 1) * size) > filesize)
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maxra = (filesize / size) - lblkno;
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/*
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* get the requested block
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*/
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*bpp = reqbp = bp = getblk(vp, lblkno, size, 0, 0, 0);
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origblkno = lblkno;
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origtotread = totread;
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/*
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* if it is in the cache, then check to see if the reads have been
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@ -141,7 +138,6 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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return 0;
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} else {
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int s;
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struct buf *tbp;
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bp->b_flags &= ~B_RAM;
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/*
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* We do the spl here so that there is no window
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@ -156,8 +152,8 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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* Stop if the buffer does not exist or it
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* is invalid (about to go away?)
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*/
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tbp = gbincore(vp, lblkno+i);
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if (tbp == NULL || (tbp->b_flags & B_INVAL))
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rbp = gbincore(vp, lblkno+i);
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if (rbp == NULL || (rbp->b_flags & B_INVAL))
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break;
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/*
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@ -166,7 +162,7 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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*/
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if (((i % racluster) == (racluster - 1)) ||
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(i == (maxra - 1)))
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tbp->b_flags |= B_RAM;
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rbp->b_flags |= B_RAM;
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}
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VI_UNLOCK(vp);
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splx(s);
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@ -183,12 +179,11 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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} else {
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off_t firstread = bp->b_offset;
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int nblks;
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int ncontigafter;
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KASSERT(bp->b_offset != NOOFFSET,
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("cluster_read: no buffer offset"));
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ncontigafter = 0;
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ncontig = 0;
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/*
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* Compute the total number of blocks that we should read
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@ -205,23 +200,23 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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*/
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if (nblks > 1) {
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error = VOP_BMAP(vp, lblkno, NULL,
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&blkno, &ncontigafter, NULL);
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&blkno, &ncontig, NULL);
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/*
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* If this failed to map just do the original block.
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*/
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if (error || blkno == -1)
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ncontigafter = 0;
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ncontig = 0;
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}
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/*
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* If we have contiguous data available do a cluster
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* otherwise just read the requested block.
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*/
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if (ncontigafter) {
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if (ncontig) {
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/* Account for our first block. */
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ncontigafter++;
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if (ncontigafter < nblks)
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nblks = ncontigafter;
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ncontig = min(ncontig + 1, nblks);
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if (ncontig < nblks)
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nblks = ncontig;
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bp = cluster_rbuild(vp, filesize, lblkno,
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blkno, size, nblks, bp);
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lblkno += (bp->b_bufsize / size);
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@ -233,44 +228,9 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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}
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/*
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* if we have been doing sequential I/O, then do some read-ahead
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*/
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rbp = NULL;
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if (seqcount && (lblkno < (origblkno + seqcount))) {
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/*
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* we now build the read-ahead buffer if it is desirable.
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*/
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if (((u_quad_t)(lblkno + 1) * size) <= filesize &&
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!(error = VOP_BMAP(vp, lblkno, NULL, &blkno, &num_ra, NULL)) &&
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blkno != -1) {
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int nblksread;
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int ntoread = num_ra + 1;
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nblksread = (origtotread + size - 1) / size;
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if (seqcount < nblksread)
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seqcount = nblksread;
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if (seqcount < ntoread)
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ntoread = seqcount;
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if (num_ra) {
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rbp = cluster_rbuild(vp, filesize, lblkno,
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blkno, size, ntoread, NULL);
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} else {
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rbp = getblk(vp, lblkno, size, 0, 0, 0);
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rbp->b_flags |= B_ASYNC | B_RAM;
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rbp->b_iocmd = BIO_READ;
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rbp->b_blkno = blkno;
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}
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}
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}
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/*
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* handle the synchronous read
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* handle the synchronous read so that it is available ASAP.
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*/
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if (bp) {
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#if defined(CLUSTERDEBUG)
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if (rcluster)
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printf("S(%ld,%ld,%d) ",
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(long)bp->b_lblkno, bp->b_bcount, seqcount);
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#endif
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if ((bp->b_flags & B_CLUSTER) == 0) {
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vfs_busy_pages(bp, 0);
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}
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@ -280,44 +240,54 @@ cluster_read(vp, filesize, lblkno, size, cred, totread, seqcount, bpp)
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BUF_KERNPROC(bp);
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error = VOP_STRATEGY(vp, bp);
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curproc->p_stats->p_ru.ru_inblock++;
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if (error)
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return (error);
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}
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/*
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* and if we have read-aheads, do them too
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* If we have been doing sequential I/O, then do some read-ahead.
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*/
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if (rbp) {
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if (error) {
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rbp->b_flags &= ~B_ASYNC;
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brelse(rbp);
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} else if (rbp->b_flags & B_CACHE) {
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while (lblkno < (origblkno + maxra)) {
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error = VOP_BMAP(vp, lblkno, NULL, &blkno, &ncontig, NULL);
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if (error)
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break;
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if (blkno == -1)
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break;
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/*
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* We could throttle ncontig here by maxra but we might as
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* well read the data if it is contiguous. We're throttled
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* by racluster anyway.
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*/
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if (ncontig) {
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ncontig = min(ncontig + 1, racluster);
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rbp = cluster_rbuild(vp, filesize, lblkno, blkno,
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size, ncontig, NULL);
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lblkno += (rbp->b_bufsize / size);
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} else {
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rbp = getblk(vp, lblkno, size, 0, 0, 0);
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rbp->b_flags |= B_ASYNC | B_RAM;
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rbp->b_iocmd = BIO_READ;
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rbp->b_blkno = blkno;
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lblkno += 1;
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}
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if (rbp->b_flags & B_CACHE) {
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rbp->b_flags &= ~B_ASYNC;
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bqrelse(rbp);
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} else {
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#if defined(CLUSTERDEBUG)
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if (rcluster) {
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if (bp)
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printf("A+");
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else
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printf("A");
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printf("(%jd,%jd,%jd,%jd) ",
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(intmax_t)rbp->b_lblkno,
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(intmax_t)rbp->b_bcount,
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(intmax_t)(rbp->b_lblkno - origblkno),
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(intmax_t)seqcount);
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}
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#endif
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if ((rbp->b_flags & B_CLUSTER) == 0) {
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vfs_busy_pages(rbp, 0);
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}
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rbp->b_flags &= ~B_INVAL;
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rbp->b_ioflags &= ~BIO_ERROR;
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if ((rbp->b_flags & B_ASYNC) || rbp->b_iodone != NULL)
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BUF_KERNPROC(rbp);
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(void) VOP_STRATEGY(vp, rbp);
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curproc->p_stats->p_ru.ru_inblock++;
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continue;
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}
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if ((rbp->b_flags & B_CLUSTER) == 0) {
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vfs_busy_pages(rbp, 0);
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}
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rbp->b_flags &= ~B_INVAL;
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rbp->b_ioflags &= ~BIO_ERROR;
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if ((rbp->b_flags & B_ASYNC) || rbp->b_iodone != NULL)
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BUF_KERNPROC(rbp);
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(void) VOP_STRATEGY(vp, rbp);
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curproc->p_stats->p_ru.ru_inblock++;
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}
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if (reqbp)
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return (bufwait(reqbp));
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else
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