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Subject: Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct
 compaction priority
To: Joonsoo Kim <iamjoonsoo.kim@lge.com>
References: <20160810091226.6709-1-vbabka@suse.cz>
 <20160810091226.6709-6-vbabka@suse.cz>
 <20160816055857.GB17448@js1304-P5Q-DELUXE>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        David Rientjes <rientjes@google.com>, Rik van Riel <riel@redhat.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
From: Vlastimil Babka <vbabka@suse.cz>
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Date: Thu, 18 Aug 2016 14:23:46 +0200
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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.