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

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Date:	Fri, 26 Jun 2015 12:04:24 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Xishi Qiu <qiuxishi@...wei.com>
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 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.

> 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.

-- 
Mel Gorman
SUSE Labs
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