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

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

On Thu, 29 Sep 2011 23:00:54 +0200
Johannes Weiner [off-list ref] wrote:

quoted

Hi,

this is the fourth revision of the memory cgroup naturalization
series.

The changes from v3 have mostly been documentation, changelog, and
naming fixes based on review feedback:

    o drop conversion of no longer existing zone-wide unevictable
      page rescue scanner
    o fix return value of mem_cgroup_hierarchical_reclaim() in
      limit-shrinking mode (Michal)
    o rename @remember to @reclaim in mem_cgroup_iter()
    o convert vm_swappiness to global_reclaim() in the
      correct patch (Michal)
    o rename
      struct mem_cgroup_iter_state -> struct mem_cgroup_reclaim_iter
      and
      struct mem_cgroup_iter -> struct mem_cgroup_reclaim_cookie
      (Michal)
    o added/amended comments and changelogs based on feedback (Michal, Kame)

Thanks for the review and feedback, guys, it's much appreciated!

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.  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?

Thanks,

	Hannes

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