linux-kernel - Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

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Date:	Fri, 20 May 2011 16:43:54 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Lutomirski <luto@....edu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	fengguang.wu@...el.com, andi@...stfloor.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, hannes@...xchg.org,
	riel@...hat.com
Subject: Re: Kernel falls apart under light memory pressure (i.e. linking
 vmlinux)

On Fri, 20 May 2011 14:36:13 +0900
Minchan Kim <minchan.kim@...il.com> wrote:

> On Fri, May 20, 2011 at 2:08 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > On Fri, 20 May 2011 13:20:15 +0900
> > Minchan Kim <minchan.kim@...il.com> wrote:
> >
> >> So I want to resolve your problem asap.
> >> We don't have see report about that. Could you do git-bisect?
> >> FYI, Recently, big change of mm is compaction,transparent huge pages.
> >> Kame, could you point out thing related to memcg if you have a mind?
> >>
> >
> > I don't doubt memcg at this stage because it never modify page->flags.
> > Consdering the case, PageActive() is set against off-LRU pages after
> > clear_active_flags() clears it.
> >
> > Hmm, I think I don't understand the lock system fully but...how do you
> > think this ?
> >
> > ==
> >
> > At splitting a hugepage, the routine marks all pmd as "splitting".
> >
> > But assume a racy case where 2 threads run into spit at the
> > same time, one thread wins compound_lock() and do split, another
> > thread should not touch splitted pages.
> 
> Sorry. Now I don't have a time to review in detail.
> When I look it roughly,  page_lock_anon_vma have to prevent it.
> But Andrea needs current this problem and he will catch something we lost. :)
> 
Hmm, maybe I miss something...need to build a test environ on my side.
But I'm not sure I can reproduce it..

Thanks,
-Kame

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