From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id E31E86B004F for ; Wed, 5 Aug 2009 03:21:13 -0400 (EDT) Received: by pzk28 with SMTP id 28so3563483pzk.11 for ; Wed, 05 Aug 2009 00:21:19 -0700 (PDT) Date: Wed, 5 Aug 2009 16:20:33 +0900 From: Minchan Kim Subject: Re: [PATCH 1/4] oom: move oom_adj to signal_struct Message-Id: <20090805162033.b8c2c74d.minchan.kim@barrios-desktop> In-Reply-To: <20090805154759.5BC2.A69D9226@jp.fujitsu.com> References: <20090805150323.2624a68f.kamezawa.hiroyu@jp.fujitsu.com> <20090805153701.b4f4385e.minchan.kim@barrios-desktop> <20090805154759.5BC2.A69D9226@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Minchan Kim , KAMEZAWA Hiroyuki , LKML , Paul Menage , David Rientjes , Rik van Riel , Andrew Morton , Linus Torvalds , Oleg Nesterov , linux-mm List-ID: On Wed, 5 Aug 2009 15:53:31 +0900 (JST) KOSAKI Motohiro wrote: > > On Wed, 5 Aug 2009 15:03:23 +0900 > > KAMEZAWA Hiroyuki wrote: > > > > > On Wed, 5 Aug 2009 14:55:16 +0900 > > > Minchan Kim wrote: > > > > > > > On Wed, 5 Aug 2009 11:51:31 +0900 (JST) > > > > KOSAKI Motohiro wrote: > > > > > > > > > > On Wed, 5 Aug 2009 11:29:34 +0900 (JST) > > > > > > KOSAKI Motohiro wrote: > > > > > > > > > > > > > Hi > > > > > > > > > > > > > > > Hi, Kosaki. > > > > > > > > > > > > > > > > I am so late to invole this thread. > > > > > > > > But let me have a question. > > > > > > > > > > > > > > > > What's advantage of placing oom_adj in singal rather than task ? > > > > > > > > I mean task->oom_adj and task->signal->oom_adj ? > > > > > > > > > > > > > > > > I am sorry if you already discussed it at last threads. > > > > > > > > > > > > > > Not sorry. that's very good question. > > > > > > > > > > > > > > I'm trying to explain the detailed intention of commit 2ff05b2b4eac > > > > > > > (move oom_adj to mm_struct). > > > > > > > > > > > > > > In 2.6.30, OOM logic callflow is here. > > > > > > > > > > > > > > __out_of_memory > > > > > > > select_bad_process for each task > > > > > > > badness calculate badness of one task > > > > > > > oom_kill_process search child > > > > > > > oom_kill_task kill target task and mm shared tasks with it > > > > > > > > > > > > > > example, process-A have two thread, thread-A and thread-B and it > > > > > > > have very fat memory. > > > > > > > And, each thread have following likes oom property. > > > > > > > > > > > > > > thread-A: oom_adj = OOM_DISABLE, oom_score = 0 > > > > > > > thread-B: oom_adj = 0, oom_score = very-high > > > > > > > > > > > > > > Then, select_bad_process() select thread-B, but oom_kill_task refuse > > > > > > > kill the task because thread-A have OOM_DISABLE. > > > > > > > __out_of_memory() call select_bad_process() again. but select_bad_process() > > > > > > > select the same task. It mean kernel fall in the livelock. > > > > > > > > > > > > > > The fact is, select_bad_process() must select killable task. otherwise > > > > > > > OOM logic go into livelock. > > > > > > > > > > > > > > Is this enough explanation? thanks. > > > > > > > > > > > > > > > The problem resulted from David patch. > > > > It can solve live lock problem but make a new problem like vfork problem. > > > > I think both can be solved by different approach. > > > > > > > > It's just RFC. > > > > > > > > If some process is selected by OOM killer but it have a child of OOM immune, > > > > We just decrease point of process. It can affect selection of bad process. > > > > After some trial, at last bad score is drastically low and another process is > > > > selected by OOM killer. So I think Live lock don't happen. > > > > > > > > New variable adding in task struct is rather high cost. > > > > But i think we can union it with oomkilladj > > > > since oomkilladj is used to present just -17 ~ 15. > > > > > > > > What do you think about this approach ? > > > > > > > keeping this in "task" struct is troublesome. > > > It may not livelock but near-to-livelock state, in bad case. > > > > Hmm. I can't understand why it is troublesome. > > I think it's related to moving oom_adj to singal_struct. > > Unfortunately, I can't understand why we have to put oom_adj > > in singal_struct? > > > > That's why I have a question to Kosaki a while ago. > > I can't understand it still. :-( > > > > Could you elaborate it ? > > Maybe, It's because my explanation is still poor. sorry. > Please give me one more chance. > > In my previous mail, I explained select_bad_process() must not > unkillable task, is this ok? > IOW, if all thread have the same oom_adj, the issue gone. > > signal_struct is shared all thread in the process. then, the issue gone. > Your and Kame's good explanation opens my eyes. :) I realized your approach's benefit. Yes. Let's wait to listen others's opinios. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org