zfsonlinux/zfs — pull request #2716 by dweeezil (2014-09-18 04:11:48+00:00)
Title: Illumos 4753 - increase number of outstanding async writes when sync tas...

...k is waiting

Reviewed by: Matthew Ahrens
Reviewed by: George Wilson
Reviewed by: Adam Leventhal
Reviewed by: Christopher Siden
Reviewed by: Dan McDonald
Approved by: Garrett D'Amore

References:
https://github.com/illumos/illumos-gate/commit/73527f441cbbd953fa42cc5a30a413bad75f24a9
https://www.illumos.org/issues/4753
https://reviews.csiden.org/r/9/

Comments by Matt Ahrens from the issue tracker:
When a sync task is waiting for a txg to complete, we should hurry
it along by increasing the number of outstanding async writes
(i.e. make vdev_queue_max_async_writes() return a larger number).
Initially we might just have a tunable for "minimum async writes
while a synctask is waiting" and set it to 3.

Ported-by: Tim Chase