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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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

> On Fri, Jan 28, 2011 at 12:26:08PM +0900, KAMEZAWA Hiroyuki wrote:
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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