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Subject: Re: [RFC 08/13] mm, compaction: simplify contended compaction
 handling
To: Michal Hocko <mhocko@kernel.org>
References: <1462865763-22084-1-git-send-email-vbabka@suse.cz>
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 <20160513130950.GN20141@dhcp22.suse.cz>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, Rik van Riel <riel@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>
From: Vlastimil Babka <vbabka@suse.cz>
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Date: Mon, 16 May 2016 09:10:41 +0200
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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.