linux-kernel - Re: Deadlock possibly caused by too_many

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Message-Id: <20101019105257.A1C6.A69D9226@jp.fujitsu.com>
Date:	Tue, 19 Oct 2010 11:03:35 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Rik van Riel <riel@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: Deadlock possibly caused by too_many_isolated.

> On Tue, Oct 19, 2010 at 10:21 AM, KOSAKI Motohiro
> <kosaki.motohiro@...fujitsu.com> wrote:
> >> On Tue, Oct 19, 2010 at 9:57 AM, KOSAKI Motohiro
> >> <kosaki.motohiro@...fujitsu.com> wrote:
> >> >> > I think there are two bugs here.
> >> >> > The raid1 bug that Torsten mentions is certainly real (and has been around
> >> >> > for an embarrassingly long time).
> >> >> > The bug that I identified in too_many_isolated is also a real bug and can be
> >> >> > triggered without md/raid1 in the mix.
> >> >> > So this is not a 'full fix' for every bug in the kernel :-), but it could
> >> >> > well be a full fix for this particular bug.
> >> >> >
> >> >>
> >> >> Can we just delete the too_many_isolated() logic?  (Crappy comment
> >> >> describes what the code does but not why it does it).
> >> >
> >> > if my remember is correct, we got bug report that LTP may makes misterious
> >> > OOM killer invocation about 1-2 years ago. because, if too many parocess are in
> >> > reclaim path, all of reclaimable pages can be isolated and last reclaimer found
> >> > the system don't have any reclaimable pages and lead to invoke OOM killer.
> >> > We have strong motivation to avoid false positive oom. then, some discusstion
> >> > made this patch.
> >> >
> >> > if my remember is incorrect, I hope Wu or Rik fix me.
> >>
> >> AFAIR, it's right.
> >>
> >> How about this?
> >>
> >> It's rather aggressive throttling than old(ie, it considers not lru
> >> type granularity but zone )
> >> But I think it can prevent unnecessary OOM problem and solve deadlock problem.
> >
> > Can you please elaborate your intention? Do you think Wu's approach is wrong?
> 
> No. I think Wu's patch may work well. But I agree Andrew.
> Couldn't we remove the too_many_isolated logic? If it is, we can solve
> the problem simply.
> But If we remove the logic, we will meet long time ago problem, again.
> So my patch's intention is to prevent OOM and deadlock problem with
> simple patch without adding new heuristic in too_many_isolated.

But your patch is much false positive/negative chance because isolated pages timing 
and too_many_isolated_zone() call site are in far distance place.
So, if anyone don't say Wu's one is wrong, I like his one.




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