linux-kernel - Re: [PATCH v2 5/5] mm/compaction: add tracepoint to observe behaviour of compaction defer

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Date:	Tue, 13 Jan 2015 09:35:26 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] mm/compaction: add tracepoint to observe behaviour
 of compaction defer

On 01/13/2015 08:18 AM, Joonsoo Kim wrote:
> On Mon, Jan 12, 2015 at 05:35:47PM +0100, Vlastimil Babka wrote:
>> Hm what if we avoided dirtying the cache line in the non-deferred case? Would be
>> simpler, too?
>> 
>> if (zone->compact_considered + 1 >= defer_limit)
>>      return false;
>> 
>> zone->compact_considered++;
>> 
>> trace_mm_compaction_defer_compaction(zone, order);
>> 
>> return true;
> 
> Okay. I will include this minor optimization in next version of this
> patch.

Hm, on second thought, the "+ 1" part would break compaction_restarting() and
it's ugly anyway. Removing "+ 1" would increase the number of
compaction_deferred() attempts until success by one. Which should be negligible,
but maybe not good to hide it in a tracepoint patch. Sorry for the noise.

> Thanks.
> 

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