From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 9F7A86B004F for ; Wed, 5 Aug 2009 02:37:46 -0400 (EDT) Received: by pzk28 with SMTP id 28so3543413pzk.11 for ; Tue, 04 Aug 2009 23:37:47 -0700 (PDT) Date: Wed, 5 Aug 2009 15:37:01 +0900 From: Minchan Kim Subject: Re: [PATCH 1/4] oom: move oom_adj to signal_struct Message-Id: <20090805153701.b4f4385e.minchan.kim@barrios-desktop> In-Reply-To: <20090805150323.2624a68f.kamezawa.hiroyu@jp.fujitsu.com> References: <20090805110107.5B97.A69D9226@jp.fujitsu.com> <20090805114004.459a7deb.minchan.kim@barrios-desktop> <20090805114650.5BA1.A69D9226@jp.fujitsu.com> <20090805145516.b2129f81.minchan.kim@barrios-desktop> <20090805150323.2624a68f.kamezawa.hiroyu@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: KAMEZAWA Hiroyuki Cc: Minchan Kim , KOSAKI Motohiro , LKML , Paul Menage , David Rientjes , Rik van Riel , Andrew Morton , Linus Torvalds , Oleg Nesterov , linux-mm List-ID: 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 ? > After applying Kosaki's , oom_kill will use > "for_each_process()" instead of "do_each_thread", I think it's a way to go. I didn't review kosaki's approach entirely. After reviewing, let's discuss it, again. > But, yes, your "scale_down" idea itself is interesitng. > Then, hmm, merging two of yours ? If it is possible, I will do so. Thnaks for good comment, kame. > Thanks, > -Kame > > > > > ---- > > > > This is based on 2.6.30 which is kernel before applying David Patch. > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index b4c38bc..6e195f7 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1150,6 +1150,11 @@ struct task_struct { > > */ > > unsigned char fpu_counter; > > s8 oomkilladj; /* OOM kill score adjustment (bit shift). */ > > + /* > > + * If OOM kill happens at one process repeately, > > + * oom_sacle_down will be increased to prevent OOM live lock > > + */ > > + unsigned int oom_scale_down; > > #ifdef CONFIG_BLK_DEV_IO_TRACE > > unsigned int btrace_seq; > > #endif > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index a7b2460..3592786 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -159,6 +159,11 @@ unsigned long badness(struct task_struct *p, unsigned long uptime) > > points >>= -(p->oomkilladj); > > } > > > > + /* > > + * adjust the score by number of OOM kill retrial > > + */ > > + points >>= p->oom_scale_down; > > + > > #ifdef DEBUG > > printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n", > > p->pid, p->comm, points); > > @@ -367,8 +372,10 @@ static int oom_kill_task(struct task_struct *p) > > * Don't kill the process if any threads are set to OOM_DISABLE > > */ > > do_each_thread(g, q) { > > - if (q->mm == mm && q->oomkilladj == OOM_DISABLE) > > + if (q->mm == mm && q->oomkilladj == OOM_DISABLE) { > > + p->oom_scale_down++; > > return 1; > > + } > > } while_each_thread(g, q); > > > > __oom_kill_task(p, 1); > > > > > > > > -- > > Kind regards, > > Minchan Kim > > > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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