linux-kernel - Re: [RFC][PATCH] prevent incorrect oom under split

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Message-ID: <28c262360806242259k3ac308c4n7cee29b72456e95b@mail.gmail.com>
Date:	Wed, 25 Jun 2008 14:59:26 +0900
From:	"MinChan Kim" <minchan.kim@...il.com>
To:	"Rik van Riel" <riel@...hat.com>,
	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	"Lee Schermerhorn" <Lee.Schermerhorn@...com>,
	akpm@...ux-foundation.org,
	"Takenori Nagano" <t-nagano@...jp.nec.com>
Subject: Re: [RFC][PATCH] prevent incorrect oom under split_lru

On Tue, Jun 24, 2008 at 10:28 PM, Rik van Riel <riel@...hat.com> wrote:
> On Tue, 24 Jun 2008 17:31:54 +0900
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
>
>> if zone->recent_scanned parameter become inbalanceing anon and file,
>> OOM killer can happened although swappable page exist.
>>
>> So, if priority==0, We should try to reclaim all page for prevent OOM.
>
> You are absolutely right.  Good catch.

I have a concern about application latency.
If lru list have many pages, it take a very long time to scan pages.
More system have many ram, More many time to scan pages.

Of course I know this is trade-off between memory efficiency VS latency.
But In embedded, some application think latency is more important
thing than memory efficiency.
We need some mechanism to cut off scanning time.


I think Takenori Nagano's "memory reclaim more efficiently patch" is
proper to reduce application latency in this case If we modify some
code.

What do you think about it ?

>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>
> Acked-by: Rik van Riel <riel@...hat.com>
>
>> ---
>>  mm/vmscan.c |    6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> Index: b/mm/vmscan.c
>> ===================================================================
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1464,8 +1464,10 @@ static unsigned long shrink_zone(int pri
>>                        * kernel will slowly sift through each list.
>>                        */
>>                       scan = zone_page_state(zone, NR_LRU_BASE + l);
>> -                     scan >>= priority;
>> -                     scan = (scan * percent[file]) / 100;
>> +                     if (priority) {
>> +                             scan >>= priority;
>> +                             scan = (scan * percent[file]) / 100;
>> +                     }
>>                       zone->lru[l].nr_scan += scan + 1;
>>                       nr[l] = zone->lru[l].nr_scan;
>>                       if (nr[l] >= sc->swap_cluster_max)
>>
>
>
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-- 
Kinds regards,
MinChan Kim
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