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

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Message-ID: <20110128075724.GB2213@cmpxchg.org>
Date:	Fri, 28 Jan 2011 08:57:24 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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, 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?

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.
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