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Date: Wed, 5 Aug 2009 15:03:23 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Minchan Kim <minchan.kim@...il.com> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, LKML <linux-kernel@...r.kernel.org>, Paul Menage <menage@...gle.com>, David Rientjes <rientjes@...gle.com>, Rik van Riel <riel@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org> Subject: Re: [PATCH 1/4] oom: move oom_adj to signal_struct On Wed, 5 Aug 2009 14:55:16 +0900 Minchan Kim <minchan.kim@...il.com> wrote: > On Wed, 5 Aug 2009 11:51:31 +0900 (JST) > KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote: > > > > On Wed, 5 Aug 2009 11:29:34 +0900 (JST) > > > KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> 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. After applying Kosaki's , oom_kill will use "for_each_process()" instead of "do_each_thread", I think it's a way to go. But, yes, your "scale_down" idea itself is interesitng. Then, hmm, merging two of yours ? 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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