linux-kernel - Re: [patch 06/12] mm: oom_kill: simplify OOM killer locking

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Date:	Thu, 26 Mar 2015 17:07:42 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Huang Ying <ying.huang@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [patch 06/12] mm: oom_kill: simplify OOM killer locking

On Thu 26-03-15 11:17:46, Johannes Weiner wrote:
> On Thu, Mar 26, 2015 at 02:31:11PM +0100, Michal Hocko wrote:
[...]
> > > @@ -795,27 +728,21 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> > >   */
> > >  void pagefault_out_of_memory(void)
> > >  {
> > > -	struct zonelist *zonelist;
> > > -
> > > -	down_read(&oom_sem);
> > >  	if (mem_cgroup_oom_synchronize(true))
> > > -		goto unlock;
> > > +		return;
> > 
> > OK, so we are back to what David has asked previously. We do not need
> > the lock for memcg and oom_killer_disabled because we know that no tasks
> > (except for potential oom victim) are lurking around at the time
> > oom_killer_disable() is called. So I guess we want to stick a comment
> > into mem_cgroup_oom_synchronize before we check for oom_killer_disabled.
> 
> I would prefer everybody that sets TIF_MEMDIE and kills a task to hold
> the lock, including memcg.  Simplicity is one thing, but also a global
> OOM kill might not even be necessary when it's racing with the memcg.

sure I am find with that.
 
> > After those are fixed, feel free to add
> > Acked-by: Michal Hocko <mhocko@...e.cz>
> 
> Thanks.

-- 
Michal Hocko
SUSE Labs
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