Re: [PATCH 12/12] cfq-iosched: add hierarchical cfq_group statistics

From: Vivek Goyal
Date: Tue Dec 18 2012 - 14:26:32 EST

On Tue, Dec 18, 2012 at 11:21:55AM -0800, Tejun Heo wrote:
> On Tue, Dec 18, 2012 at 02:18:54PM -0500, Vivek Goyal wrote:
> > > Yeah, hmmm, maybe we should add another set of counters to carry stats
> > > from dead ones? Avoiding hierarchical accounting overhead in hot path
> > > while remembering by-gones shouldn't be that hard. Will work on that.
> >
> > So are you planning to migrate the stats to parent when a cgroup is being
> > deleted? That should make sure we don't do hierarhical update.
> Yeah, something like that. The current statistics being !hierarchical
> means that we need to keep them separate from the actual stats, so
> it'll end up with another set of stats. Kinda nasty but I don't see
> any better way out.

Separate stats for hierarchical migration make sense to me.

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