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Illumos 6450 - scrub/resilver unnecessarily traverses snapshots

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6450 scrub/resilver unnecessarily traverses snapshots created
after the scrub started
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/issues/6450
  https://github.com/illumos/illumos-gate/commit/38d6103

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Matthew Ahrens 2016-01-30 21:40:28 +01:00 committed by Brian Behlendorf
parent 9d36cdb650
commit b77222c873
1 changed files with 50 additions and 4 deletions
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54
module/zfs/dsl_scan.c
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@ -872,7 +872,16 @@ dsl_scan_ds_destroyed(dsl_dataset_t *ds, dmu_tx_t *tx)
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; "
@ -912,9 +921,6 @@ dsl_scan_ds_destroyed(dsl_dataset_t *ds, dmu_tx_t *tx)
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);
}
/*
@ -1068,6 +1074,46 @@ dsl_scan_visitds(dsl_scan_t *scn, uint64_t dsobj, dmu_tx_t *tx)
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;