linux-kernel - Re: [PATCH] mm: fix set pageblock migratetype when boot

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Date:	Fri, 26 Jun 2015 19:25:03 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>, <sasha.levin@...cle.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix set pageblock migratetype when boot

On 2015/6/26 19:04, Mel Gorman wrote:

> On Fri, Jun 26, 2015 at 06:09:05PM +0800, Xishi Qiu wrote:
>> memmap_init_zone()
>> 	...
>> 	if ((z->zone_start_pfn <= pfn)
>> 	    && (pfn < zone_end_pfn(z))
>> 	    && !(pfn & (pageblock_nr_pages - 1)))
>> 		set_pageblock_migratetype(page, MIGRATE_MOVABLE);
>> 	...
>>
>> If the pfn does not align to pageblock, it will not init the migratetype.
> 
> What important impact does that have? It should leave a partial pageblock
> as MIGRATE_UNMOVABLE which is fine by me.
> 

Hi Mel,

The impact is less, it's OK to ignore it.

Thanks,
Xishi Qiu

>> So call it for every page, it will takes more time, but it doesn't matter, 
>> this function will be called only in boot or hotadd memory.
>>
> 
> It's a lot of additional overhead to add to memory initialisation. It
> would need to be for an excellent reason with no alternative solution.
> 



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