[dm-devel] [PATCH] dm-kcopyd: monitor io activity
Joe Thornber
ejt at redhat.com
Tue May 31 09:09:01 UTC 2011
On Mon, May 30, 2011 at 12:40:39PM -0400, Mikulas Patocka wrote:
> Here I'm sending three patches that limit kcopyd speed. There is global
> limit for all kcopyds running in a system. The user can set percentage of
> kcopyd speed in /sys/module/dm_mod/parameters/dm_kcopyd_throttle
Could you give some explanation of how to choose an appropriate value
for this please? Should it be 100% unless there is an issue? How
does the sys admin spot such issues?
Different kcopyd clients have different performance requirements, for
instance the initial sync of a new mirror leg may have less priority
than a copy-on-write exception for a snapshot. This isn't something
we've addressed so far, but if you're starting to slow kcopyd down
(i.e. so the mirror sync doesn't saturate the system), then I think
you'll get some complaints from the snapshot users.
- joe
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