lkml.org 
[lkml]   [2016]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3 13/17] mm, compaction: use correct watermark when checking allocation success
From
Date
On 07/06/2016 07:47 AM, Joonsoo Kim wrote:
> On Fri, Jun 24, 2016 at 11:54:33AM +0200, Vlastimil Babka wrote:
>> The __compact_finished() function uses low watermark in a check that has to
>> pass if the direct compaction is to finish and allocation should succeed. This
>> is too pessimistic, as the allocation will typically use min watermark. It may
>> happen that during compaction, we drop below the low watermark (due to parallel
>> activity), but still form the target high-order page. By checking against low
>> watermark, we might needlessly continue compaction.
>>
>> Similarly, __compaction_suitable() uses low watermark in a check whether
>> allocation can succeed without compaction. Again, this is unnecessarily
>> pessimistic.
>>
>> After this patch, these check will use direct compactor's alloc_flags to
>> determine the watermark, which is effectively the min watermark.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> ---
>> mm/compaction.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 76897850c3c2..371760a85085 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1320,7 +1320,7 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_
>> return COMPACT_CONTINUE;
>>
>> /* Compaction run is not finished if the watermark is not met */
>> - watermark = low_wmark_pages(zone);
>> + watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK];
>
> finish condition is changed. We have two more watermark checks in
> try_to_compact_pages() and kcompactd_do_work() and they should be
> changed too.

Ugh, I've completely missed them. Thanks for catching this, hopefully
fixing that will improve the results.

\
 
 \ /
  Last update: 2016-07-18 12:01    [W:0.143 / U:1.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site