linux-kernel - Re: [PATCH] mm: check zone->all_unreclaimable in all

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Message-ID: <4D72580D.4000208@gmail.com>
Date:	Sat, 05 Mar 2011 18:34:37 +0300
From:	Andrew Vagin <avagin@...il.com>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	Andrey Vagin <avagin@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: check zone->all_unreclaimable in all_unreclaimable()

On 03/05/2011 06:20 PM, Minchan Kim wrote:
> On Sat, Mar 05, 2011 at 02:44:16PM +0300, Andrey Vagin wrote:
>> Check zone->all_unreclaimable in all_unreclaimable(), otherwise the
>> kernel may hang up, because shrink_zones() will do nothing, but
>> all_unreclaimable() will say, that zone has reclaimable pages.
>>
>> do_try_to_free_pages()
>> 	shrink_zones()
>> 		 for_each_zone
>> 			if (zone->all_unreclaimable)
>> 				continue
>> 	if !all_unreclaimable(zonelist, sc)
>> 		return 1
>>
>> __alloc_pages_slowpath()
>> retry:
>> 	did_some_progress = do_try_to_free_pages(page)
>> 	...
>> 	if (!page&&  did_some_progress)
>> 		retry;
>>
>> Signed-off-by: Andrey Vagin<avagin@...nvz.org>
>> ---
>>   mm/vmscan.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 6771ea7..1c056f7 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2002,6 +2002,8 @@ static bool all_unreclaimable(struct zonelist *zonelist,
>>
>>   	for_each_zone_zonelist_nodemask(zone, z, zonelist,
>>   			gfp_zone(sc->gfp_mask), sc->nodemask) {
>> +		if (zone->all_unreclaimable)
>> +			continue;
>>   		if (!populated_zone(zone))
>>   			continue;
>>   		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
>
> zone_reclaimable checks it. Isn't it enough?
I sent one more patch [PATCH] mm: skip zombie in OOM-killer.
This two patches are enough.
> Does the hang up really happen or see it by code review?
Yes. You can reproduce it for help the attached python program. It's not 
very clever:)
It make the following actions in loop:
1. fork
2. mmap
3. touch memory
4. read memory
5. munmmap

>> -- 
>> 1.7.1
>>
>> --
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