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SubjectRe: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority
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On 08/16/2016 08:07 AM, Joonsoo Kim wrote:
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> ---
>> mm/page_alloc.c | 18 +++++++++++-------
>> 1 file changed, 11 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index fb975cec3518..b28517b918b0 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3155,13 +3155,8 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
>> * so it doesn't really make much sense to retry except when the
>> * failure could be caused by insufficient priority
>> */
>> - if (compaction_failed(compact_result)) {
>> - if (*compact_priority > MIN_COMPACT_PRIORITY) {
>> - (*compact_priority)--;
>> - return true;
>> - }
>> - return false;
>> - }
>> + if (compaction_failed(compact_result))
>> + goto check_priority;
>>
>> /*
>> * make sure the compaction wasn't deferred or didn't bail out early
>> @@ -3185,6 +3180,15 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
>> if (compaction_retries <= max_retries)
>> return true;
>>
>> + /*
>> + * Make sure there is at least one attempt at the highest priority
>> + * if we exhausted all retries at the lower priorities
>> + */
>> +check_priority:
>> + if (*compact_priority > MIN_COMPACT_PRIORITY) {
>> + (*compact_priority)--;
>> + return true;
>> + }
>> return false;
>
> The only difference that this patch makes is increasing priority when
> COMPACT_PARTIAL(COMPACTION_SUCCESS) returns. In that case, we can

Hm it's true that I adjusted this patch from the previous version,
before realizing that PARTIAL is now SUCCESS.

> usually allocate high-order freepage so we would not enter here. Am I
> missing something? Is it really needed behaviour change?

It will likely be rare when this triggers, when compaction success
doesn't lead to allocation success due to parallel allocation activity.

> Thanks.
>

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