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7504 kmem_reap hangs spa_sync and administrative tasks

Description

7504 kmem_reap hangs spa_sync and administrative tasks

illumos/illumos-gate@405a5a0f5c3ab36cb76559467d1a62ba648bd809
https://github.com/illumos/illumos-gate/commit/405a5a0f5c3ab36cb76559467d1a62ba648bd80

https://www.illumos.org/issues/7504

We see long spa_sync(). We are waiting to hold dp_config_rwlock for writer. Some
other thread holds dp_config_rwlock for reader, then calls arc_get_data_buf(),
which finds that arc_is_overflowing()==B_TRUE. So it waits (while holding
dp_config_rwlock for reader) for arc_reclaim_thread to signal arc_reclaim_waiters_cv.
Before signaling, arc_reclaim_thread does arc_kmem_reap_now(), which takes ~seconds.

Author: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>

Details

Provenance
jpaetzelAuthored on
Parents
rS313875: mtx: microoptimize lockstat handling in __mtx_lock_sleep
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