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

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Date:	Thu, 19 May 2011 23:38:06 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	minchan.kim@...il.com, kamezawa.hiroyu@...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 Thu, May 19, 2011 at 11:12 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> Right after that happened, I hit ctrl-c to kill test_mempressure.sh.
>> The system was OK until I typed sync, and then everything hung.
>>
>> I'm really confused.  shrink_inactive_list in
>> RECLAIM_MODE_LUMPYRECLAIM will call one of the isolate_pages functions
>> with ISOLATE_BOTH.  The resulting list goes into shrink_page_list,
>> which does VM_BUG_ON(PageActive(page)).
>>
>> How is that supposed to work?
>
> Usually clear_active_flags() clear PG_active before calling
> shrink_page_list().
>
> shrink_inactive_list()
>    isolate_pages_global()
>    update_isolated_counts()
>        clear_active_flags()
>    shrink_page_list()
>
>

That makes sense.  And I have CONFIG_COMPACTION=y, so the lumpy mode
doesn't get set anyway.

But the pages I'm seeing have flags=100000000008005D.  If I'm reading
it right, that means locked,referenced,uptodate,dirty,active.  How
does a page like that end up in shrink_page_list?  I don't see how a
page that's !PageLRU can get marked Active.  Nonetheless, I'm hitting
that VM_BUG_ON.

Is there a race somewhere?

--Andy
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