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

[Zhang Yanfei]

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@xxxxxxxxxxxxxx>
>>
>> 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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