linux-kernel - Re: [RFC 08/13] mm, compaction: simplify contended compaction handling

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Message-ID: <57397271.50504@suse.cz>
Date:	Mon, 16 May 2016 09:10:41 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC 08/13] mm, compaction: simplify contended compaction
 handling

On 05/13/2016 03:09 PM, Michal Hocko wrote:
>> >@@ -1564,14 +1564,11 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
>> >  	trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
>> >  				cc->free_pfn, end_pfn, sync, ret);
>> >
>> >-	if (ret == COMPACT_CONTENDED)
>> >-		ret = COMPACT_PARTIAL;
>> >-
>> >  	return ret;
>> >  }
> This took me a while to grasp but then I realized this is correct
> because we shouldn't pretend progress when there was none in fact,
> especially when __alloc_pages_direct_compact basically replaced this
> "fake" COMPACT_PARTIAL by COMPACT_CONTENDED anyway.

Yes. Actually COMPACT_CONTENDED compact_result used to be just for the 
tracepoint, and __alloc_pages_direct_compact used another function 
parameter to signal contention. You changed it with the oom rework so 
COMPACT_CONTENDED result value was used, so this hunk just makes sure 
it's still reported correctly.