linux-kernel - Re: [PATCH] Make is_mem_section_removable more conformable with offlining code

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Date:	Tue, 31 Aug 2010 22:59:22 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Mel Gorman <mel@...ux.vnet.ibm.com>, Michal Hocko <mhocko@...e.cz>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	Haicheng Li <haicheng.li@...ux.intel.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Make is_mem_section_removable more conformable with
 offlining code

On Tue, Aug 31, 2010 at 10:36:49PM +0800, Wu Fengguang wrote:
> On Tue, Aug 31, 2010 at 10:19:42PM +0800, Wu Fengguang wrote:
> > On Mon, Aug 23, 2010 at 05:22:46PM +0800, Michal Hocko wrote:
> > > On Sun 22-08-10 08:42:32, Wu Fengguang wrote:
> > > > Hi Michal,
> > > 
> > > Hi,
> > > 
> > > > 
> > > > It helps to explain in changelog/code
> > > > 
> > > > - in what situation a ZONE_MOVABLE will contain !MIGRATE_MOVABLE
> > > >   pages? 
> > > 
> > > page can be MIGRATE_RESERVE IIUC.
> > 
> > Yup, it may also be set to MIGRATE_ISOLATE by soft_offline_page().
> 
> Ah a non-movable page allocation could fall back into the movable
> zone. See __rmqueue_fallback() and the fallbacks[][] array. So the
> 
>         if (type != MIGRATE_MOVABLE && !pageblock_free(page))
> 
> check in is_mem_section_removable() is correct. It is
> set_migratetype_isolate() that should be fixed to use the same check.

Mel, I'm not familiar with the code, but it seems that in
__rmqueue_fallback(), set_pageblock_migratetype() is not always called
after move_freepages_block() successfully moved some pages. Then it's
possible a MIGRATE_MOVABLE page block will end up containing
non-movable pages?

Thanks,
Fengguang
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