linux-kernel - Re: [PATCH -v2 2/5] OOM: thaw the OOM victim if it is frozen

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Message-ID: <20141207185533.GA29065@dhcp22.suse.cz>
Date:	Sun, 7 Dec 2014 19:55:33 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	"\\\"Rafael J. Wysocki\\\"" <rjw@...ysocki.net>,
	David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH -v2 2/5] OOM: thaw the OOM victim if it is frozen

On Sun 07-12-14 08:59:40, Tejun Heo wrote:
> On Sun, Dec 07, 2014 at 11:45:39AM +0100, Michal Hocko wrote:
> ....
> >  void mark_tsk_oom_victim(struct task_struct *tsk)
> >  {
> >  	set_tsk_thread_flag(tsk, TIF_MEMDIE);
> > +	__thaw_task(tsk);
> 
> Yeah, this is a lot better.  Maybe we can add a comment at least
> pointing readers to where to look at to understand what's going on?
> This stems from the fact that OOM killer which essentially is a memory
> reclaim operation overrides freezing.  It'd be nice if that is
> documented somehow.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 19a08f3f00ba..fca456fe855a 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -426,6 +426,13 @@ void note_oom_kill(void)
 void mark_tsk_oom_victim(struct task_struct *tsk)
 {
 	set_tsk_thread_flag(tsk, TIF_MEMDIE);
+
+	/*
+	 * Make sure that the task is woken up from uninterruptible sleep
+	 * if it is frozen because OOM killer wouldn't be able to free
+	 * any memory and livelock. freezing_slow_path will tell the freezer
+	 * that TIF_MEMDIE tasks should be ignored.
+	 */
 	__thaw_task(tsk);
 }

Better?
-- 
Michal Hocko
SUSE Labs
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