linux-kernel - Re: [patch] oom: give current access to memory reserves if it has been killed

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Message-ID: <alpine.DEB.2.00.1003311641470.2150@chino.kir.corp.google.com>
Date:	Wed, 31 Mar 2010 16:48:31 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	anfei <anfei.zhou@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	nishimura@....nes.nec.co.jp,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] oom: give current access to memory reserves if it has
 been killed

On Thu, 1 Apr 2010, Oleg Nesterov wrote:

> > Why? You ignored this part:
> >
> > 	Say, right after exit_mm() we are doing acct_process(), and f_op->write()
> > 	needs a page. So, you are saying that in this case __page_cache_alloc()
> > 	can never trigger out_of_memory() ?
> >
> > why this is not possible?
> >
> > David, I am not arguing, I am asking.
> 
> In case I wasn't clear...
> 
> Yes, currently __oom_kill_task(p) is not possible if p->mm == NULL.
> 
> But your patch adds
> 
> 	if (fatal_signal_pending(current))
> 		__oom_kill_task(current);
> 
> into out_of_memory().
> 

Ok, and it's possible during the tasklist scan if current is PF_EXITING 
and that gets passed to oom_kill_process(), so we need the following 
patch.  Can I have your acked-by and then I'll propose it to Andrew with a 
follow-up that merges __oom_kill_task() into oom_kill_task() since it only 
has one caller now anyway?

 [ Both of these situations will be current since the oom killer is a 
   no-op whenever another task is found to be PF_EXITING and
   oom_kill_process() wouldn't get called with any other thread unless
   oom_kill_quick is enabled or its VM_FAULT_OOM in which cases we kill 
   current as well. ]

Thanks Oleg.
---
 mm/oom_kill.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -459,7 +459,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 	 * its children or threads, just set TIF_MEMDIE so it can die quickly
 	 */
 	if (p->flags & PF_EXITING) {
-		__oom_kill_task(p);
+		set_tsk_thread_flag(p, TIF_MEMDIE);
 		return 0;
 	}
 
@@ -686,7 +686,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	 * its memory.
 	 */
 	if (fatal_signal_pending(current)) {
-		__oom_kill_task(current);
+		set_tsk_thread_flag(current, TIF_MEMDIE);
 		return;
 	}
 
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