linux-kernel - Re: [BUGFIX][PATCH 2/4] memcg: fix charge path for THP and allow early retirement

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Message-Id: <20110128171447.1b5b19f3.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 28 Jan 2011 17:14:47 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [BUGFIX][PATCH 2/4] memcg: fix charge path for THP and allow
 early retirement

On Fri, 28 Jan 2011 08:57:24 +0100
Johannes Weiner <hannes@...xchg.org> wrote:

> On Fri, Jan 28, 2011 at 12:26:08PM +0900, KAMEZAWA Hiroyuki wrote:
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > 
> > When THP is used, Hugepage size charge can happen. It's not handled
> > correctly in mem_cgroup_do_charge(). For example, THP can fallback
> > to small page allocation when HUGEPAGE allocation seems difficult
> > or busy, but memory cgroup doesn't understand it and continue to
> > try HUGEPAGE charging. And the worst thing is memory cgroup
> > believes 'memory reclaim succeeded' if limit - usage > PAGE_SIZE.
> > 
> > By this, khugepaged etc...can goes into inifinite reclaim loop
> > if tasks in memcg are busy.
> > 
> > After this patch 
> >  - Hugepage allocation will fail if 1st trial of page reclaim fails.
> > 
> > Changelog:
> >  - make changes small. removed renaming codes.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> >  mm/memcontrol.c |   28 ++++++++++++++++++++++++----
> >  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> Was there something wrong with my oneline fix?
> 
I thought your patch was against RHEL6.

> Really, there is no way to make this a beautiful fix.  The way this
> function is split up makes no sense, and the constant addition of more
> and more flags just to correctly communicate with _one callsite_
> should be an obvious hint.
> 

Your version has to depend on oom_check flag to work fine.
I think it's complicated.

Thanks,
-Kame



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