Date: Mon, 22 Jan 2018 05:55:43 +0000 (UTC) From: Alexander Motin <mav@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-vendor@freebsd.org Subject: svn commit: r328253 - vendor-sys/illumos/dist/uts/common/fs/zfs Message-ID: <201801220555.w0M5th55062500@repo.freebsd.org>
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Author: mav Date: Mon Jan 22 05:55:43 2018 New Revision: 328253 URL: https://svnweb.freebsd.org/changeset/base/328253 Log: 8835 Speculative prefetch in ZFS not working for misaligned reads illumos/illumos-gate@5cb8d943bc8513c6230589aad5a409d58b0297cb https://www.illumos.org/issues/8835: Sequential reads not aligned to block size are not detected by ZFS prefetcher as sequential, killing prefetch and severely hurting performance. It is caused by dmu_zfetch() in case of misaligned sequential accesses being called with overlap of one block. Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: Allan Jude <allanjude@freebsd.org> Approved by: Gordon Ross <gwr@nexenta.com> Author: Alexander Motin <mav@FreeBSD.org> Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_zfetch.c Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_zfetch.c ============================================================================== --- vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_zfetch.c Mon Jan 22 05:52:39 2018 (r328252) +++ vendor-sys/illumos/dist/uts/common/fs/zfs/dmu_zfetch.c Mon Jan 22 05:55:43 2018 (r328253) @@ -224,19 +224,33 @@ dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblk rw_enter(&zf->zf_rwlock, RW_READER); + /* + * Find matching prefetch stream. Depending on whether the accesses + * are block-aligned, first block of the new access may either follow + * the last block of the previous access, or be equal to it. + */ for (zs = list_head(&zf->zf_stream); zs != NULL; zs = list_next(&zf->zf_stream, zs)) { - if (blkid == zs->zs_blkid) { + if (blkid == zs->zs_blkid || blkid + 1 == zs->zs_blkid) { mutex_enter(&zs->zs_lock); /* * zs_blkid could have changed before we * acquired zs_lock; re-check them here. */ - if (blkid != zs->zs_blkid) { - mutex_exit(&zs->zs_lock); - continue; + if (blkid == zs->zs_blkid) { + break; + } else if (blkid + 1 == zs->zs_blkid) { + blkid++; + nblks--; + if (nblks == 0) { + /* Already prefetched this before. */ + mutex_exit(&zs->zs_lock); + rw_exit(&zf->zf_rwlock); + return; + } + break; } - break; + mutex_exit(&zs->zs_lock); } }
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