linux-kernel - Re: [PATCH] mm: get rid of unnecessary pageblock scanning in setup_zone_migrate

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Date:	Thu, 31 Oct 2013 13:14:43 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	kosaki.motohiro@...il.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, akpm@...ux-foundation.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH] mm: get rid of unnecessary pageblock scanning in setup_zone_migrate_reserve

>> Nit. I would like to add following hunk. This is just nit because moving
>> reserve pageblock is extreme rare.
>>
>> 		if (block_migratetype == MIGRATE_RESERVE) {
>> +                       found++;
>> 			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
>> 			move_freepages_block(zone, page, MIGRATE_MOVABLE);
>> 		}
>
> I don't really see the advantage but if you think it is necessary then I
> do not object either.

For example, a zone has five pageblock b1,b2,b3,b4,b5 and b1 has MIGRATE_RESERVE.
When hotremove b1 and hotadd again, your code need to scan all of blocks. But
mine only need to scan b1 and b2. I mean that's a hotplug specific optimization.


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