On Fri, 30 Sep 2011 11:32:31 +0200
Johannes Weiner [off-list ref] wrote:

On Fri, Sep 30, 2011 at 05:05:10PM +0900, KAMEZAWA Hiroyuki wrote:

quoted

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!

quoted

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.


Thanks,
-Kame

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