linux-kernel - Re: [PATCH] fix mem_cgroup_split_huge

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Date:	Mon, 21 Nov 2011 19:44:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>, cgroups@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	mhocko@...e.cz, Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH] fix mem_cgroup_split_huge_fixup to work efficiently.

On Mon, 21 Nov 2011 11:42:50 +0100
Johannes Weiner <hannes@...xchg.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@...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@...xchg.org>

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

Thanks,
-Kame


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