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Reduce number of arc_prune threads

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On FreeBSD vnode reclamation is single-threaded, protected by single
global lock.  Linux seems to be able to use a thread per mount point,
but at this time it creates more harm than good.

Reduce number of threads to 1, adding tunable in case somebody wants
to try more.

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Chris Dunlop <chris@onthe.net.au>
Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Closes #12896
Issue #9966
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Alexander Motin 2021-12-22 20:07:13 -05:00 committed by GitHub
parent d2f374c3f2
commit 462217d1c2
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2 changed files with 17 additions and 3 deletions
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7
man/man4/zfs.4
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@ -676,6 +676,13 @@ Minimum time "prescient prefetched" blocks are locked in the ARC.
These blocks are meant to be prefetched fairly aggressively ahead of
the code that may use them.
.
.It Sy zfs_arc_prune_task_threads Ns = Ns Sy 1 Pq int
Number of arc_prune threads.
.Fx
does not need more than one.
Linux may theoretically use one per mount point up to number of CPUs,
but that was not proven to be useful.
.
.It Sy zfs_max_missing_tvds Ns = Ns Sy 0 Pq int
Number of missing top-level vdevs which will be allowed during
pool import (only in read-only mode).

13
module/zfs/arc.c
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@ -463,6 +463,11 @@ int zfs_arc_meta_strategy = ARC_STRATEGY_META_BALANCED;
int zfs_arc_meta_adjust_restarts = 4096;
int zfs_arc_lotsfree_percent = 10;
/*
* Number of arc_prune threads
*/
static int zfs_arc_prune_task_threads = 1;
/* The 6 states: */
arc_state_t ARC_anon;
arc_state_t ARC_mru;
@ -7983,9 +7988,8 @@ arc_init(void)
offsetof(arc_prune_t, p_node));
mutex_init(&arc_prune_mtx, NULL, MUTEX_DEFAULT, NULL);
arc_prune_taskq = taskq_create("arc_prune", 100, defclsyspri,
boot_ncpus, INT_MAX, TASKQ_PREPOPULATE | TASKQ_DYNAMIC |
TASKQ_THREADS_CPU_PCT);
arc_prune_taskq = taskq_create("arc_prune", zfs_arc_prune_task_threads,
defclsyspri, 100, INT_MAX, TASKQ_PREPOPULATE | TASKQ_DYNAMIC);
arc_ksp = kstat_create("zfs", 0, "arcstats", "misc", KSTAT_TYPE_NAMED,
sizeof (arc_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL);
@ -11132,4 +11136,7 @@ ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, eviction_pct, INT, ZMOD_RW,
ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, evict_batch_limit, INT, ZMOD_RW,
"The number of headers to evict per sublist before moving to the next");
ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, prune_task_threads, INT, ZMOD_RW,
"Number of arc_prune threads");
/* END CSTYLED */