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Fix hung z_zvol tasks during 'zfs receive'

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During a receive operation zvol_create_minors_impl() can wait
needlessly for the prefetch thread because both share the same tasks
queue.  This results in hung tasks:

<3>INFO: task z_zvol:5541 blocked for more than 120 seconds.
<3>      Tainted: P           O  3.16.0-4-amd64
<3>"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

The first z_zvol:5541 (zvol_task_cb) is waiting for the long running
traverse_prefetch_thread:260

root@linux:~# cat /proc/spl/taskq
taskq                       act  nthr  spwn  maxt   pri  mina
spl_system_taskq/0            1     2     0    64   100     1
	active: [260]traverse_prefetch_thread [zfs](0xffff88003347ae40)
	wait: 5541
spl_delay_taskq/0             0     1     0     4   100     1
	delay: spa_deadman [zfs](0xffff880039924000)
z_zvol/1                      1     1     0     1   120     1
	active: [5541]zvol_task_cb [zfs](0xffff88001fde6400)
	pend: zvol_task_cb [zfs](0xffff88001fde6800)

This change adds a dedicated, per-pool, prefetch taskq to prevent the
traverse code from monopolizing the global (and limited) system_taskq by
inappropriately scheduling long running tasks on it.

Reviewed-by: Albert Lee <trisk@forkgnu.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6330
Closes #6890
Closes #7343
This commit is contained in:
LOLi 2018-03-30 21:10:01 +02:00 committed by Tony Hutter
parent 3b118f0a34
commit fd01167ffd
3 changed files with 16 additions and 1 deletions
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1
include/sys/spa_impl.h
View File

@ -275,6 +275,7 @@ struct spa {
spa_stats_t spa_stats; /* assorted spa statistics */
hrtime_t spa_ccw_fail_time; /* Conf cache write fail time */
taskq_t *spa_zvol_taskq; /* Taskq for minor management */
taskq_t *spa_prefetch_taskq; /* Taskq for prefetch threads */
uint64_t spa_multihost; /* multihost aware (mmp) */
mmp_thread_t spa_mmp; /* multihost mmp thread */

3
module/zfs/dmu_traverse.c
View File

@ -31,6 +31,7 @@
#include <sys/dsl_pool.h>
#include <sys/dnode.h>
#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/zio.h>
#include <sys/dmu_impl.h>
#include <sys/sa.h>
@ -623,7 +624,7 @@ traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp,
}
if (!(flags & TRAVERSE_PREFETCH_DATA) ||
taskq_dispatch(system_taskq, traverse_prefetch_thread,
taskq_dispatch(spa->spa_prefetch_taskq, traverse_prefetch_thread,
td, TQ_NOQUEUE) == TASKQID_INVALID)
pd->pd_exited = B_TRUE;

13
module/zfs/spa.c
View File

@ -1182,6 +1182,14 @@ spa_activate(spa_t *spa, int mode)
spa->spa_zvol_taskq = taskq_create("z_zvol", 1, defclsyspri,
1, INT_MAX, 0);
/*
* Taskq dedicated to prefetcher threads: this is used to prevent the
* pool traverse code from monopolizing the global (and limited)
* system_taskq by inappropriately scheduling long running tasks on it.
*/
spa->spa_prefetch_taskq = taskq_create("z_prefetch", boot_ncpus,
defclsyspri, 1, INT_MAX, TASKQ_DYNAMIC);
/*
* The taskq to upgrade datasets in this pool. Currently used by
* feature SPA_FEATURE_USEROBJ_ACCOUNTING.
@ -1211,6 +1219,11 @@ spa_deactivate(spa_t *spa)
spa->spa_zvol_taskq = NULL;
}
if (spa->spa_prefetch_taskq) {
taskq_destroy(spa->spa_prefetch_taskq);
spa->spa_prefetch_taskq = NULL;
}
if (spa->spa_upgrade_taskq) {
taskq_destroy(spa->spa_upgrade_taskq);
spa->spa_upgrade_taskq = NULL;