lkml.org 
[lkml]   [2013]   [Mar]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 05/10] mm: vmscan: Do not allow kswapd to scan at maximum priority
On 03/21/2013 06:12 AM, Mel Gorman wrote:
> On Wed, Mar 20, 2013 at 09:20:14PM -0400, Rik van Riel wrote:
>> On 03/17/2013 09:04 AM, Mel Gorman wrote:
>>> Page reclaim at priority 0 will scan the entire LRU as priority 0 is
>>> considered to be a near OOM condition. Kswapd can reach priority 0 quite
>>> easily if it is encountering a large number of pages it cannot reclaim
>>> such as pages under writeback. When this happens, kswapd reclaims very
>>> aggressively even though there may be no real risk of allocation failure
>>> or OOM.
>>>
>>> This patch prevents kswapd reaching priority 0 and trying to reclaim
>>> the world. Direct reclaimers will still reach priority 0 in the event
>>> of an OOM situation.
>>>
>>> Signed-off-by: Mel Gorman <mgorman@suse.de>
>>> ---
>>> mm/vmscan.c | 2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index 7513bd1..af3bb6f 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -2891,7 +2891,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>>> */
>>> if (raise_priority || !this_reclaimed)
>>> sc.priority--;
>>> - } while (sc.priority >= 0 &&
>>> + } while (sc.priority >= 1 &&
>>> !pgdat_balanced(pgdat, order, *classzone_idx));
>>>
>>> out:
>>>
>>
>> If priority 0 is way way way way way too aggressive, what makes
>> priority 1 safe?
>>
>
> The fact that priority 1 selects a sensible number of pages to reclaim and
> obeys swappiness makes it a lot safer. Priority 0 does this in get_scan_count
^^^^^^^^^^^^^^^^

Ahhh, good point! We stay away from all the "emergency" code, which
kswapd should never run.

Acked-by: Rik van Riel <riel@redhat.com>

--
All rights reversed


\
 
 \ /
  Last update: 2013-03-21 14:01    [W:0.093 / U:1.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site