linux-kernel - Re: [PATCH v2 2/4] mm/compaction: stop the isolation when we isolate enough freepage

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Date:	Sat, 31 Jan 2015 18:17:55 +0800
From:	Zhang Yanfei <zhangyanfei.ok@...mail.com>
To:	Vlastimil Babka <vbabka@...e.cz>, Joonsoo Kim <js1304@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Mel Gorman <mgorman@...e.de>, David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 2/4] mm/compaction: stop the isolation when we isolate
 enough freepage

At 2015/1/31 16:31, Vlastimil Babka wrote:
> On 01/31/2015 08:49 AM, Zhang Yanfei wrote:
>> Hello,
>>
>> At 2015/1/30 20:34, Joonsoo Kim wrote:
>>
>> Reviewed-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>
>>
>> IMHO, the patch making the free scanner move slower makes both scanners
>> meet further. Before this patch, if we isolate too many free pages and even 
>> after we release the unneeded free pages later the free scanner still already
>> be there and will be moved forward again next time -- the free scanner just
>> cannot be moved back to grab the free pages we released before no matter where
>> the free pages in, pcp or buddy. 
> 
> It can be actually moved back. If we are releasing free pages, it means the
> current compaction is terminating, and it will set zone->compact_cached_free_pfn
> back to the position of the released free page that was furthest back. The next
> compaction will start from the cached free pfn.

Yeah, you are right. I missed the release_freepages(). Thanks!

> 
> It is however possible that another compaction runs in parallel and has
> progressed further and overwrites the cached free pfn.
> 

Hmm, maybe.

Thanks.
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