* question: should_compact_retry limit
@ 2019-06-04 23:30 Mike Kravetz
2019-06-05 7:58 ` Vlastimil Babka
0 siblings, 1 reply; 4+ messages in thread
From: Mike Kravetz @ 2019-06-04 23:30 UTC (permalink / raw)
To: linux-mm, linux-kernel; +Cc: Vlastimil Babka, Michal Hocko
While looking at some really long hugetlb page allocation times, I noticed
instances where should_compact_retry() was returning true more often that
I expected. In one allocation attempt, it returned true 765668 times in a
row. To me, this was unexpected because of the following:
#define MAX_COMPACT_RETRIES 16
int max_retries = MAX_COMPACT_RETRIES;
However, if should_compact_retry() returns true via the following path we
do not increase the retry count.
/*
* make sure the compaction wasn't deferred or didn't bail out early
* due to locks contention before we declare that we should give up.
* But do not retry if the given zonelist is not suitable for
* compaction.
*/
if (compaction_withdrawn(compact_result)) {
ret = compaction_zonelist_suitable(ac, order, alloc_flags);
goto out;
}
Just curious, is this intentional?
--
Mike Kravetz
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: question: should_compact_retry limit
2019-06-04 23:30 question: should_compact_retry limit Mike Kravetz
@ 2019-06-05 7:58 ` Vlastimil Babka
2019-06-05 16:05 ` Mike Kravetz
0 siblings, 1 reply; 4+ messages in thread
From: Vlastimil Babka @ 2019-06-05 7:58 UTC (permalink / raw)
To: Mike Kravetz, linux-mm, linux-kernel; +Cc: Michal Hocko
On 6/5/19 1:30 AM, Mike Kravetz wrote:
> While looking at some really long hugetlb page allocation times, I noticed
> instances where should_compact_retry() was returning true more often that
> I expected. In one allocation attempt, it returned true 765668 times in a
> row. To me, this was unexpected because of the following:
>
> #define MAX_COMPACT_RETRIES 16
> int max_retries = MAX_COMPACT_RETRIES;
>
> However, if should_compact_retry() returns true via the following path we
> do not increase the retry count.
>
> /*
> * make sure the compaction wasn't deferred or didn't bail out early
> * due to locks contention before we declare that we should give up.
> * But do not retry if the given zonelist is not suitable for
> * compaction.
> */
> if (compaction_withdrawn(compact_result)) {
> ret = compaction_zonelist_suitable(ac, order, alloc_flags);
> goto out;
> }
>
> Just curious, is this intentional?
Hmm I guess we didn't expect compaction_withdrawn() to be so
consistently returned. Do you know what value of compact_result is there
in your test?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: question: should_compact_retry limit
2019-06-05 7:58 ` Vlastimil Babka
@ 2019-06-05 16:05 ` Mike Kravetz
2019-06-05 16:33 ` Vlastimil Babka
0 siblings, 1 reply; 4+ messages in thread
From: Mike Kravetz @ 2019-06-05 16:05 UTC (permalink / raw)
To: Vlastimil Babka, linux-mm, linux-kernel; +Cc: Michal Hocko
On 6/5/19 12:58 AM, Vlastimil Babka wrote:
> On 6/5/19 1:30 AM, Mike Kravetz wrote:
>> While looking at some really long hugetlb page allocation times, I noticed
>> instances where should_compact_retry() was returning true more often that
>> I expected. In one allocation attempt, it returned true 765668 times in a
>> row. To me, this was unexpected because of the following:
>>
>> #define MAX_COMPACT_RETRIES 16
>> int max_retries = MAX_COMPACT_RETRIES;
>>
>> However, if should_compact_retry() returns true via the following path we
>> do not increase the retry count.
>>
>> /*
>> * make sure the compaction wasn't deferred or didn't bail out early
>> * due to locks contention before we declare that we should give up.
>> * But do not retry if the given zonelist is not suitable for
>> * compaction.
>> */
>> if (compaction_withdrawn(compact_result)) {
>> ret = compaction_zonelist_suitable(ac, order, alloc_flags);
>> goto out;
>> }
>>
>> Just curious, is this intentional?
>
> Hmm I guess we didn't expect compaction_withdrawn() to be so
> consistently returned. Do you know what value of compact_result is there
> in your test?
Added some instrumentation to record values and ran test,
557904 Total
549186 COMPACT_DEFERRED
8718 COMPACT_PARTIAL_SKIPPED
Do note that this is not my biggest problem with these allocations. That is
should_continue_reclaim returning true more often that in should. Still
trying to get more info on that. This was just something curious I also
discovered.
--
Mike Kravetz
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: question: should_compact_retry limit
2019-06-05 16:05 ` Mike Kravetz
@ 2019-06-05 16:33 ` Vlastimil Babka
0 siblings, 0 replies; 4+ messages in thread
From: Vlastimil Babka @ 2019-06-05 16:33 UTC (permalink / raw)
To: Mike Kravetz, linux-mm, linux-kernel; +Cc: Michal Hocko
On 6/5/19 6:05 PM, Mike Kravetz wrote:
> On 6/5/19 12:58 AM, Vlastimil Babka wrote:
>> On 6/5/19 1:30 AM, Mike Kravetz wrote:
>> Hmm I guess we didn't expect compaction_withdrawn() to be so
>> consistently returned. Do you know what value of compact_result is there
>> in your test?
>
> Added some instrumentation to record values and ran test,
>
> 557904 Total
>
> 549186 COMPACT_DEFERRED
Retrying mindlessly with compaction deferred sounds definitely wrong,
I'll try to look at it. Thanks.
> 8718 COMPACT_PARTIAL_SKIPPED
>
> Do note that this is not my biggest problem with these allocations. That is
> should_continue_reclaim returning true more often that in should. Still
> trying to get more info on that. This was just something curious I also
> discovered.
>
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-06-05 16:37 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-04 23:30 question: should_compact_retry limit Mike Kravetz
2019-06-05 7:58 ` Vlastimil Babka
2019-06-05 16:05 ` Mike Kravetz
2019-06-05 16:33 ` Vlastimil Babka
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