linux-kernel - Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority

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Date:	Thu, 18 Aug 2016 14:23:46 +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 05/11] mm, compaction: add the ultimate direct
 compaction priority

On 08/16/2016 07:58 AM, Joonsoo Kim wrote:
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -1644,6 +1644,8 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
>>  		.alloc_flags = alloc_flags,
>>  		.classzone_idx = classzone_idx,
>>  		.direct_compaction = true,
>> +		.whole_zone = (prio == COMPACT_PRIO_SYNC_FULL),
>> +		.ignore_skip_hint = (prio == COMPACT_PRIO_SYNC_FULL)
>>  	};
>>  	INIT_LIST_HEAD(&cc.freepages);
>>  	INIT_LIST_HEAD(&cc.migratepages);
>> @@ -1689,7 +1691,8 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
>>  								ac->nodemask) {
>>  		enum compact_result status;
>>
>> -		if (compaction_deferred(zone, order)) {
>> +		if (prio > COMPACT_PRIO_SYNC_FULL
>> +					&& compaction_deferred(zone, order)) {
>>  			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
>>  			continue;
>
> Could we provide prio to compaction_deferred() and do the decision in
> that that function?
>
> BTW, in kcompactd, compaction_deferred() is checked but
> .ignore_skip_hint=true. Is there any reason? If we can remove
> compaction_deferred() for kcompactd, we can check .ignore_skip_hint
> to determine if defer is needed or not.

I don't want to change kcompactd right now, as the current series seems 
to help against premature OOMs. But I'll revisit it later.

Thanks.