Re: [patch 00/10] memcg naturalization -rc4

From: KAMEZAWA Hiroyuki
Date: Mon Oct 03 2011 - 06:05:20 EST

On Fri, 30 Sep 2011 11:32:31 +0200
Johannes Weiner <jweiner@xxxxxxxxxx> wrote:

> On Fri, Sep 30, 2011 at 05:05:10PM +0900, KAMEZAWA Hiroyuki wrote:
> > On Thu, 29 Sep 2011 23:00:54 +0200
> > Thank you for your work. Now, I'm ok this series to be tested in -mm.
> > Ack. to all.
> Thanks!
> > Do you have any plan, concerns ?
> I would really like to get them into 3.2. While it's quite intrusive,
> I stress-tested various scenarios for quite some time - tests that
> revealed more bugs in the existing memcg code than in my changes - so
> I don't expect too big surprises. AFAICS, Google uses these patches
> internally already and their bug reports early on also helped iron out
> the most obvious problems.
> What I am concerned about is the scalability on setups with thousands
> of tiny memcgs that go into global reclaim, as this would try to scan
> pages from all existing memcgs. There is a mitigating factor in that
> concurrent reclaimers divide the memcgs to scan among themselves (the
> shared mem_cgroup_reclaim_iter), and with hundreds or thousands of
> memcgs, I expect several threads to go into reclaim upon global memory
> pressure at the same time in the common case. I don't have the means
> to test this and I also don't know if such setups exist or are within
> the realm of sanity that we would like to support, anyway.

As far as I hear, some users use hundreds of memcg in a host.

> If this
> shows up, I think the fix would be as easy as bailing out early from
> the hierarchy walk, but I would like to cross that bridge when we come
> to it.
> Other than that, I see no reason to hold it off. Traditional reclaim
> without memcgs except root_mem_cgroup - what most people care about -
> is mostly unaffected. There is a real interest in the series, and
> maintaining it out-of-tree is a major pain and quite error prone.
> What do you think?

I think this should be merged/tested as soon as possible because this patch
must be a base for memcg patches which are now being developped.


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