From: Oleg Nesterov <oleg@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Andrew Morton <akpm@linux-foundation.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Hugh Dickins <hughd@google.com>,
linux-mm@kvack.org, Andrey Vagin <avagin@openvz.org>
Subject: Re: [patch] oom: prevent unnecessary oom kills or kernel panics
Date: Wed, 9 Mar 2011 12:06:06 +0100 [thread overview]
Message-ID: <20110309110606.GA16719@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1103081549530.27910@chino.kir.corp.google.com>
On 03/08, David Rientjes wrote:
>
> On Tue, 8 Mar 2011, Oleg Nesterov wrote:
>
> > > > By iterating over threads instead, it is possible to detect threads that
> > > > are exiting and nominate them for oom kill so they get access to memory
> > > > reserves.
> > >
> > > In fact, PF_EXITING is a sing of *THREAD* exiting, not process. Therefore
> > > PF_EXITING is not a sign of memory freeing in nearly future. If other
> > > CPUs don't try to free memory, prevent oom and waiting makes deadlock.
> >
> > I agree. I don't understand this patch.
> >
>
> Using for_each_process() does not consider threads that have failed to
> exit after the oom killed parent and, thus, we select another innocent
> task to kill when we're really just waiting for those threads to exit
How so? select_bad_process() checks TIF_MEMDIE and returns ERR_PTR()
if it is set.
And, exactly because we use for_each_process() we do not need to check
other threads. The main thread can't disappear until they all exit.
Imho TIF_MEMDIE is not perfect and should be replaced by MMF_, but this
is another story. Hmm... and in any case, currently TIF_MEMDIE is not
always used correctly, afaics.
> The end result is that without this patch, we sometimes unnecessarily
> panic (and "sometimes" is defined as "many machines" for us) when nothing
> else is eligible for kill within an oom cpuset yet doing a
> do_each_thread() over that cpuset shows threads of previously oom killed
> parent that have yet to exit.
>
> > > > @@ -324,7 +324,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
> > > > * the process of exiting and releasing its resources.
> > > > * Otherwise we could get an easy OOM deadlock.
> > > > */
> > > > - if (thread_group_empty(p) && (p->flags & PF_EXITING) && p->mm) {
> > > > + if ((p->flags & PF_EXITING) && p->mm) {
> >
> > The previous check was not perfect, we know this.
> >
> > But with this patch applied, the simple program below disables oom-killer
> > completely. select_bad_process() can never succeed.
> >
>
> The program illustrates a problem that shouldn't be fixed in
> select_bad_process() but rather in oom_kill_process() when choosing an
> eligible child of the selected task to kill in place of its parent.
Can't understand. oom_kill_process() is never called exactly because
select_bad_process() is fooled.
Oleg.
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next prev parent reply other threads:[~2011-03-09 11:14 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-01 19:09 [patch] oom: prevent unnecessary oom kills or kernel panics David Rientjes
2011-03-03 1:20 ` KOSAKI Motohiro
2011-03-03 19:53 ` David Rientjes
2011-03-06 11:14 ` KOSAKI Motohiro
2011-03-06 22:06 ` David Rientjes
2011-03-08 0:24 ` KOSAKI Motohiro
2011-03-08 2:01 ` KOSAKI Motohiro
2011-03-08 13:42 ` Oleg Nesterov
2011-03-08 23:57 ` David Rientjes
2011-03-09 10:36 ` KOSAKI Motohiro
2011-03-09 11:06 ` Oleg Nesterov [this message]
2011-03-09 20:32 ` David Rientjes
2011-03-10 12:05 ` Oleg Nesterov
2011-03-10 15:40 ` [PATCH 0/1] Was: " Oleg Nesterov
2011-03-10 15:41 ` [PATCH 1/1] oom_kill_task: mark every thread as TIF_MEMDIE Oleg Nesterov
2011-03-13 1:08 ` David Rientjes
2011-03-10 16:36 ` [PATCH 0/1] select_bad_process: improve the PF_EXITING check Oleg Nesterov
2011-03-10 16:37 ` [PATCH 1/1] " Oleg Nesterov
2011-03-10 16:40 ` [PATCH 0/1] " Oleg Nesterov
2011-03-10 17:18 ` [PATCH v2 " Oleg Nesterov
2011-03-10 17:19 ` [PATCH v2 1/1] " Oleg Nesterov
2011-03-13 1:06 ` [patch] oom: prevent unnecessary oom kills or kernel panics David Rientjes
2011-03-09 23:19 ` Andrew Morton
2011-03-11 19:45 ` David Rientjes
2011-03-12 12:34 ` Oleg Nesterov
2011-03-12 13:43 ` [PATCH 0/3] oom: TIF_MEMDIE/PF_EXITING fixes Oleg Nesterov
2011-03-12 13:44 ` [PATCH 1/3] oom: oom_kill_task: mark every thread as TIF_MEMDIE Oleg Nesterov
2011-03-13 1:14 ` David Rientjes
2011-03-12 13:44 ` [PATCH 2/3] oom: select_bad_process: improve the PF_EXITING check Oleg Nesterov
2011-03-12 13:44 ` [PATCH 3/3] oom: select_bad_process: use same_thread_group() Oleg Nesterov
2011-03-12 19:40 ` [PATCH 0/3] oom: TIF_MEMDIE/PF_EXITING fixes Hugh Dickins
2011-03-13 8:53 ` KOSAKI Motohiro
2011-03-13 21:27 ` Oleg Nesterov
2011-03-14 19:04 ` [PATCH 0/3 for 2.6.38] oom: fixes Oleg Nesterov
2011-03-14 19:04 ` [PATCH 1/3 for 2.6.38] oom: oom_kill_process: don't set TIF_MEMDIE if !p->mm Oleg Nesterov
2011-03-14 19:35 ` Linus Torvalds
2011-03-14 20:31 ` Oleg Nesterov
2011-03-14 20:32 ` David Rientjes
2011-03-15 19:12 ` Oleg Nesterov
2011-03-15 19:51 ` David Rientjes
2011-03-14 20:22 ` David Rientjes
2011-03-15 18:53 ` Oleg Nesterov
2011-03-15 19:54 ` David Rientjes
2011-03-15 21:16 ` Oleg Nesterov
2011-03-14 19:05 ` [PATCH 2/3 for 2.6.38] oom: select_bad_process: ignore TIF_MEMDIE zombies Oleg Nesterov
2011-03-14 20:50 ` David Rientjes
2011-03-14 19:05 ` [PATCH 3/3 for 2.6.38] oom: oom_kill_process: fix the child_points logic Oleg Nesterov
2011-03-14 20:41 ` David Rientjes
2011-03-15 19:21 ` Oleg Nesterov
2011-03-13 11:36 ` [PATCH 0/3] oom: TIF_MEMDIE/PF_EXITING fixes KOSAKI Motohiro
2011-03-13 1:11 ` [patch] oom: prevent unnecessary oom kills or kernel panics David Rientjes
2011-03-13 1:15 ` [patch -mm] oom: avoid deferring oom killer if exiting task is being traced David Rientjes
2011-03-14 17:40 ` Oleg Nesterov
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