linux-kernel - Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority

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Message-ID: <d32f4619-e7a8-863a-bf94-4cbc0b452630@suse.cz>
Date:	Tue, 16 Aug 2016 08:31:13 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct
 compaction priority

On 08/16/2016 08:07 AM, Joonsoo Kim wrote:
>> Signed-off-by: Vlastimil Babka <vbabka@...e.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.
>