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SubjectRe: cgroup memory, blkio and the lovely swapping
On Fri, 4 Mar 2011 09:11:32 +0100
Daniel Poelzleithner <poelzi@poelzi.org> wrote:

> On Fri, 4 Mar 2011 16:54:55 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > Now, blkio cgroup does work only with synchronous I/O(direct I/O)
> > and never work with swap I/O. And I don't think swap-i/o limit
> > is a blkio matter.
>
> I'm totally unsure about what subsystem it really belongs to. It is
> memory for sure, but disk access, which it actually affects, belongs to
> the blkio subsystem. Is there a technical reason why swap I/O is not run
> through the blkio system ?
>

Now, blkio cgroup has no tags on each page. Then, it works only when
it can detect a thread which starts I/O in block layer.
But there is an activity to fix that.

http://marc.info/?l=linux-mm&m=129888823027871&w=2

I think you can discuss swap io handling in this thread.

>
> > Memory cgroup is now developping dirty_ratio for memory cgroup.
> > By that, you can control the number of pages in writeback, in memory
> > cgroup. I think it will work for you.
>
> I'm not sure that fixes the fairness problem on swapio. Just having a
> larger buffer before a writeback happens will reduce seeks, but not
> give fair share of io in swap in. It's good to control over it on
> cgroup level, but i doubt it will fix the problem.
>

swap-in is out-of-control from memcg's view and have no plans.
IHMO, the number of swap-in will be blkio cgroup matter.

Thanks,
-Kame



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