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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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