Author: mav
Date: Mon Mar 21 00:15:41 2016
New Revision: 297110
URL: https://svnweb.freebsd.org/changeset/base/297110
Log:
MFC r296514: MFV r296513:
6450 scrub/resilver unnecessarily traverses snapshots created after the
scrub started
Reviewed by: George Wilson <george.wil...@delphix.com>
Reviewed by: Prakash Surya <prakash.su...@delphix.com>
Reviewed by: Richard Elling <richard.ell...@richardelling.com>
Approved by: Richard Lowe <richl...@richlowe.net>
Author: Matthew Ahrens <mahr...@delphix.com>
illumos/illumos-gate@38d61036746e2273cc18f6698392e1e29f87d1bf
Modified:
stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
==============================================================================
--- stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c Mon Mar
21 00:14:30 2016 (r297109)
+++ stable/10/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c Mon Mar
21 00:15:41 2016 (r297110)
@@ -856,7 +856,16 @@ dsl_scan_ds_destroyed(dsl_dataset_t *ds,
if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
if (ds->ds_is_snapshot) {
- /* Note, scn_cur_{min,max}_txg stays the same. */
+ /*
+ * Note:
+ * - scn_cur_{min,max}_txg stays the same.
+ * - Setting the flag is not really necessary if
+ * scn_cur_max_txg == scn_max_txg, because there
+ * is nothing after this snapshot that we care
+ * about. However, we set it anyway and then
+ * ignore it when we retraverse it in
+ * dsl_scan_visitds().
+ */
scn->scn_phys.scn_bookmark.zb_objset =
dsl_dataset_phys(ds)->ds_next_snap_obj;
zfs_dbgmsg("destroying ds %llu; currently traversing; "
@@ -896,9 +905,6 @@ dsl_scan_ds_destroyed(dsl_dataset_t *ds,
zfs_dbgmsg("destroying ds %llu; in queue; removing",
(u_longlong_t)ds->ds_object);
}
- } else {
- zfs_dbgmsg("destroying ds %llu; ignoring",
- (u_longlong_t)ds->ds_object);
}
/*
@@ -1051,6 +1057,46 @@ dsl_scan_visitds(dsl_scan_t *scn, uint64
VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
+ if (scn->scn_phys.scn_cur_min_txg >=
+ scn->scn_phys.scn_max_txg) {
+ /*
+ * This can happen if this snapshot was created after the
+ * scan started, and we already completed a previous snapshot
+ * that was created after the scan started. This snapshot
+ * only references blocks with:
+ *
+ * birth < our ds_creation_txg
+ * cur_min_txg is no less than ds_creation_txg.
+ * We have already visited these blocks.
+ * or
+ * birth > scn_max_txg
+ * The scan requested not to visit these blocks.
+ *
+ * Subsequent snapshots (and clones) can reference our
+ * blocks, or blocks with even higher birth times.
+ * Therefore we do not need to visit them either,
+ * so we do not add them to the work queue.
+ *
+ * Note that checking for cur_min_txg >= cur_max_txg
+ * is not sufficient, because in that case we may need to
+ * visit subsequent snapshots. This happens when min_txg > 0,
+ * which raises cur_min_txg. In this case we will visit
+ * this dataset but skip all of its blocks, because the
+ * rootbp's birth time is < cur_min_txg. Then we will
+ * add the next snapshots/clones to the work queue.
+ */
+ char *dsname = kmem_alloc(MAXNAMELEN, KM_SLEEP);
+ dsl_dataset_name(ds, dsname);
+ zfs_dbgmsg("scanning dataset %llu (%s) is unnecessary because "
+ "cur_min_txg (%llu) >= max_txg (%llu)",
+ dsobj, dsname,
+ scn->scn_phys.scn_cur_min_txg,
+ scn->scn_phys.scn_max_txg);
+ kmem_free(dsname, MAXNAMELEN);
+
+ goto out;
+ }
+
if (dmu_objset_from_ds(ds, &os))
goto out;
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