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    SubjectRe: [PATCH] fix mem_cgroup_split_huge_fixup to work efficiently.
    On Mon, 21 Nov 2011 11:42:50 +0100
    Johannes Weiner <hannes@cmpxchg.org> wrote:

    > On Thu, Nov 17, 2011 at 10:33:08AM +0900, KAMEZAWA Hiroyuki wrote:
    > >
    > > I'll send this again when mm is shipped.
    > > I sometimes see mem_cgroup_split_huge_fixup() in perf report and noticed
    > > it's very slow. This fixes it. Any comments are welcome.
    > >
    > > ==
    > > Subject: [PATCH] fix mem_cgroup_split_huge_fixup to work efficiently.
    > >
    > > at split_huge_page(), mem_cgroup_split_huge_fixup() is called to
    > > handle page_cgroup modifcations. It takes move_lock_page_cgroup()
    > > and modify page_cgroup and LRU accounting jobs and called
    > > HPAGE_PMD_SIZE - 1 times.
    > >
    > > But thinking again,
    > > - compound_lock() is held at move_accout...then, it's not necessary
    > > to take move_lock_page_cgroup().
    > > - LRU is locked and all tail pages will go into the same LRU as
    > > head is now on.
    > > - page_cgroup is contiguous in huge page range.
    > >
    > > This patch fixes mem_cgroup_split_huge_fixup() as to be called once per
    > > hugepage and reduce costs for spliting.
    > >
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > I agree with the changes, but since you are resending it anyway: I
    > think removing the move_lock and switching the hook to take care of
    > all tail pages in one go are two logical steps. Would you mind
    > breaking it up into separate patches?
    >
    > In any case,
    >
    > Acked-by: Johannes Weiner <hannes@cmpxchg.org>

    Ok, I'll break this into 2 patches at resending.

    Thanks,
    -Kame




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