linux-kernel - Re: [patch 1/2] mm, memcg: avoid oom notification when current needs access to memory reserves

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Message-ID: <20131118125507.GD32623@dhcp22.suse.cz>
Date:	Mon, 18 Nov 2013 13:55:07 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [patch 1/2] mm, memcg: avoid oom notification when current needs
 access to memory reserves

On Mon 18-11-13 13:52:40, Michal Hocko wrote:
> [Adding Eric to CC]
> 
> On Thu 14-11-13 15:26:51, David Rientjes wrote:
> > When current has a pending SIGKILL or is already in the exit path, it
> > only needs access to memory reserves to fully exit.  In that sense, the
> > memcg is not actually oom for current, it simply needs to bypass memory
> > charges to exit and free its memory, which is guarantee itself that
> > memory will be freed.
> > 
> > We only want to notify userspace for actionable oom conditions where
> > something needs to be done (and all oom handling can already be deferred
> > to userspace through this method by disabling the memcg oom killer with
> > memory.oom_control), not simply when a memcg has reached its limit, which
> > would actually have to happen before memcg reclaim actually frees memory
> > for charges.
> 
> I believe this also fixes the issue reported by Eric
> (https://lkml.org/lkml/2013/7/28/74). I had a patch for this
> https://lkml.org/lkml/2013/7/31/94 but the code changed since then and
> this should be equivalent.
>  
> > Reported-by: Johannes Weiner <hannes@...xchg.org>
> > Signed-off-by: David Rientjes <rientjes@...gle.com>

Anyway, the patch looks good to me but please mention the above bug in
the changelog.

Acked-by: Michal Hocko <mhocko@...e.cz>

> > ---
> >  mm/memcontrol.c | 20 ++++++++++----------
> >  1 file changed, 10 insertions(+), 10 deletions(-)
> > 
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1783,16 +1783,6 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >  	unsigned int points = 0;
> >  	struct task_struct *chosen = NULL;
> >  
> > -	/*
> > -	 * If current has a pending SIGKILL or is exiting, then automatically
> > -	 * select it.  The goal is to allow it to allocate so that it may
> > -	 * quickly exit and free its memory.
> > -	 */
> > -	if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
> > -		set_thread_flag(TIF_MEMDIE);
> > -		return;
> > -	}
> > -
> >  	check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
> >  	totalpages = mem_cgroup_get_limit(memcg) >> PAGE_SHIFT ? : 1;
> >  	for_each_mem_cgroup_tree(iter, memcg) {
> > @@ -2243,6 +2233,16 @@ bool mem_cgroup_oom_synchronize(bool handle)
> >  	if (!handle)
> >  		goto cleanup;
> >  
> > +	/*
> > +	 * If current has a pending SIGKILL or is exiting, then automatically
> > +	 * select it.  The goal is to allow it to allocate so that it may
> > +	 * quickly exit and free its memory.
> > +	 */
> > +	if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
> > +		set_thread_flag(TIF_MEMDIE);
> > +		goto cleanup;
> > +	}
> > +
> >  	owait.memcg = memcg;
> >  	owait.wait.flags = 0;
> >  	owait.wait.func = memcg_oom_wake_function;
> 
> -- 
> Michal Hocko
> SUSE Labs
> --
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-- 
Michal Hocko
SUSE Labs
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