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Increase default zfs_scan_vdev_limit to 16MB 

For HDD based pools the default zfs_scan_vdev_limit of 4M
per-vdev can significantly limit the maximum scrub performance.
Increasing the default to 16M can double the scrub speed from
80 MB/s per disk to 160 MB/s per disk.

This does increase the memory footprint during scrub/resilver
but given the performance win this is a reasonable trade off.
Memory usage is capped at 1/4 of arc_c_max.  Note that number
of outstanding I/Os has not changed and is still limited by
zfs_vdev_scrub_max_active.

Reviewed-by: Akash B <akash-b@hpe.com>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #14428
This commit is contained in:
Brian Behlendorf 2023-01-24 14:05:45 -08:00
parent dc5c8006f6
commit c0aea7cf4e
2 changed files with 17 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
man/man4/zfs.4
View File

@ -1905,7 +1905,7 @@ When disabled, the memory limit may be exceeded by fast disks.
Freezes a scrub/resilver in progress without actually pausing it.
Intended for testing/debugging.
.
.It Sy zfs_scan_vdev_limit Ns = Ns Sy 4194304 Ns B Po 4 MiB Pc Pq int
.It Sy zfs_scan_vdev_limit Ns = Ns Sy 16777216 Ns B Po 16 MiB Pc Pq int
Maximum amount of data that can be concurrently issued at once for scrubs and
resilvers per leaf device, given in bytes.
.

28
module/zfs/dsl_scan.c
View File

@ -37,6 +37,7 @@
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/arc.h>
#include <sys/arc_impl.h>
#include <sys/zap.h>
#include <sys/zio.h>
#include <sys/zfs_context.h>
@ -126,7 +127,7 @@ static boolean_t scan_ds_queue_contains(dsl_scan_t *scn, uint64_t dsobj,
static void scan_ds_queue_insert(dsl_scan_t *scn, uint64_t dsobj, uint64_t txg);
static void scan_ds_queue_remove(dsl_scan_t *scn, uint64_t dsobj);
static void scan_ds_queue_sync(dsl_scan_t *scn, dmu_tx_t *tx);
static uint64_t dsl_scan_count_data_disks(vdev_t *vd);
static uint64_t dsl_scan_count_data_disks(spa_t *spa);
extern uint_t zfs_vdev_async_write_active_min_dirty_percent;
static int zfs_scan_blkstats = 0;
@ -156,7 +157,7 @@ static int zfs_scan_strict_mem_lim = B_FALSE;
* overload the drives with I/O, since that is protected by
* zfs_vdev_scrub_max_active.
*/
static uint64_t zfs_scan_vdev_limit = 4 << 20;
static uint64_t zfs_scan_vdev_limit = 16 << 20;
static uint_t zfs_scan_issue_strategy = 0;
@ -475,11 +476,12 @@ dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
/*
* Calculate the max number of in-flight bytes for pool-wide
* scanning operations (minimum 1MB). Limits for the issuing
* phase are done per top-level vdev and are handled separately.
* scanning operations (minimum 1MB, maximum 1/4 of arc_c_max).
* Limits for the issuing phase are done per top-level vdev and
* are handled separately.
*/
scn->scn_maxinflight_bytes = MAX(zfs_scan_vdev_limit *
dsl_scan_count_data_disks(spa->spa_root_vdev), 1ULL << 20);
scn->scn_maxinflight_bytes = MIN(arc_c_max / 4, MAX(1ULL << 20,
zfs_scan_vdev_limit * dsl_scan_count_data_disks(spa)));
avl_create(&scn->scn_queue, scan_ds_queue_compare, sizeof (scan_ds_t),
offsetof(scan_ds_t, sds_node));
@ -2823,8 +2825,9 @@ dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
}
static uint64_t
dsl_scan_count_data_disks(vdev_t *rvd)
dsl_scan_count_data_disks(spa_t *spa)
{
vdev_t *rvd = spa->spa_root_vdev;
uint64_t i, leaves = 0;
for (i = 0; i < rvd->vdev_children; i++) {
@ -3733,12 +3736,13 @@ dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
taskqid_t prefetch_tqid;
/*
* Recalculate the max number of in-flight bytes for pool-wide
* scanning operations (minimum 1MB). Limits for the issuing
* phase are done per top-level vdev and are handled separately.
* Calculate the max number of in-flight bytes for pool-wide
* scanning operations (minimum 1MB, maximum 1/4 of arc_c_max).
* Limits for the issuing phase are done per top-level vdev and
* are handled separately.
*/
scn->scn_maxinflight_bytes = MAX(zfs_scan_vdev_limit *
dsl_scan_count_data_disks(spa->spa_root_vdev), 1ULL << 20);
scn->scn_maxinflight_bytes = MIN(arc_c_max / 4, MAX(1ULL << 20,
zfs_scan_vdev_limit * dsl_scan_count_data_disks(spa)));
if (scnp->scn_ddt_bookmark.ddb_class <=
scnp->scn_ddt_class_max) {