Re: [RFC] writeback and cgroup

From: Vivek Goyal
Date: Wed Apr 18 2012 - 14:19:44 EST

On Tue, Apr 17, 2012 at 02:48:31PM -0700, Tejun Heo wrote:

> As for priority inversion through shared request pool, it is a problem
> which needs to be solved regardless of how async IOs are throttled.
> I'm not determined to which extent yet tho. Different cgroups
> definitely need to be on separate pools but do we also want
> distinguish sync and async and what about ioprio? Maybe we need a
> bybrid approach with larger common pool and reserved ones for each
> class?

currently we have global pool with separate limits for sync and async
and there is no consideration of ioprio. I think to keep it simple we
can just extend the same notion to keep per cgroup pool with internal
limits on sync/async requests to make sure sync IO does not get
serialized behind async IO. Personally I am not too worried about
async IO prio. It has never worked.

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