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    SubjectRe: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock (Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure)
    On Thu, Mar 11, 2010 at 11:54:13AM -0500, Vivek Goyal wrote:
    > On Thu, Mar 11, 2010 at 01:49:08PM +0900, KAMEZAWA Hiroyuki wrote:
    > > On Thu, 11 Mar 2010 13:31:23 +0900
    > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
    > >
    > > > On Wed, 10 Mar 2010 09:26:24 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > > > > * nishimura@mxp.nes.nec.co.jp <nishimura@mxp.nes.nec.co.jp> [2010-03-10 10:43:09]:
    > >
    > > > I made a patch(attached) using both local_irq_disable/enable and local_irq_save/restore.
    > > > local_irq_save/restore is used only in mem_cgroup_update_file_mapped.
    > > >
    > > > And I attached a histogram graph of 30 times kernel build in root cgroup for each.
    > > >
    > > > before_root: no irq operation(original)
    > > > after_root: local_irq_disable/enable for all
    > > > after2_root: local_irq_save/restore for all
    > > > after3_root: mixed version(attached)
    > > >
    > > > hmm, there seems to be a tendency that before < after < after3 < after2 ?
    > > > Should I replace save/restore version to mixed version ?
    > > >
    > >
    > > IMHO, starting from after2_root version is the easist.
    > > If there is a chance to call lock/unlock page_cgroup can be called in
    > > interrupt context, we _have to_ disable IRQ, anyway.
    > > And if we have to do this, I prefer migration_lock rather than this mixture.
    > >
    > > BTW, how big your system is ? Balbir-san's concern is for bigger machines.
    > > But I'm not sure this change is affecte by the size of machines.
    > > I'm sorry I have no big machine, now.
    >
    > FWIW, I took andrea's patches (local_irq_save/restore solution) and
    > compiled the kernel on 32 cores hyperthreaded (64 cpus) with make -j32
    > in /dev/shm/. On this system, I can't see much difference.
    >
    > I compiled the kernel 10 times and took average.
    >
    > Without andrea's patches: 28.698 (seconds)
    > With andrea's patches: 28.711 (seconds).
    > Diff is .04%
    >
    > This is all should be in root cgroup. Note, I have not mounted memory cgroup
    > controller but it is compiled in. So I am assuming that root group
    > accounting will still be taking place. Also assuming that it is not
    > required to do actual IO to disk and /dev/shm is enough to see the results
    > of local_irq_save()/restore.

    cgroup disable is at boot time "cgroup_disable=...", so root cgroup
    accounting should be enabled.

    The same for the local_irq_save/restore() overhead, lock/unlock_page_cgroup()
    is called during each charge.

    Many thanks for testing!
    -Andrea


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