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    SubjectRe: Help Resource Counters Scale better (v4)
    * Andrew Morton <akpm@linux-foundation.org> [2009-08-11 16:31:59]:

    > On Tue, 11 Aug 2009 20:14:05 +0530
    > Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    >
    > > Enhancement: Remove the overhead of root based resource counter accounting
    > >
    > > From: Balbir Singh <balbir@linux.vnet.ibm.com>
    > >
    > > This patch reduces the resource counter overhead (mostly spinlock)
    > > associated with the root cgroup. This is a part of the several
    > > patches to reduce mem cgroup overhead. I had posted other
    > > approaches earlier (including using percpu counters). Those
    > > patches will be a natural addition and will be added iteratively
    > > on top of these.
    > >
    > > The patch stops resource counter accounting for the root cgroup.
    > > The data for display is derived from the statisitcs we maintain
    > > via mem_cgroup_charge_statistics (which is more scalable).
    > >
    > > The tests results I see on a 24 way show that
    > >
    > > 1. The lock contention disappears from /proc/lock_stats
    > > 2. The results of the test are comparable to running with
    > > cgroup_disable=memory.
    > >
    > > Please test/review.
    >
    > I don't get it.
    >
    > The patch apepars to skip accounting altogether for the root memcgroup
    > and then adds some accounting back in for swap. Or something like
    > that. How come? Do we actually not need the root memcgroup
    > accounting?
    >

    The changelog mentions that the statistics are derived. For memsw as
    Daisuke-San mentioned, the SWAP accounting is for memsw. We can derive
    memory.usage_in_bytes from RSS+Cache fields in the memory.stat
    accounting. For memsw, we needed SWAP accounting.


    > IOW, the changelog sucks ;)
    >
    > Is this an alternative approach to using percpu_counters, or do we do
    > both or do we choose one or the other? res_counter_charge() really is
    > quite sucky.
    >
    > The patch didn't have a signoff.
    >
    > It would be nice to finalise those performance testing results and
    > include them in the new, improved patch description.
    >

    I'll submit a new patch with better changelog, checkpatch.pl fixes and
    test results.


    --
    Balbir


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