linux-kernel - Re: [PATCH 1/3] mm: fix set pageblock migratetype in deferred struct page init

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Date:	Tue, 16 Aug 2016 11:23:45 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm: fix set pageblock migratetype in deferred struct
 page init

On Tue 16-08-16 16:56:54, Xishi Qiu wrote:
> On 2016/8/16 16:41, Michal Hocko wrote:
> 
> > On Thu 04-08-16 19:25:03, Xishi Qiu wrote:
> >> MAX_ORDER_NR_PAGES is usually 4M, and a pageblock is usually 2M, so we only
> >> set one pageblock's migratetype in deferred_free_range() if pfn is aligned
> >> to MAX_ORDER_NR_PAGES.
> > 
> > Do I read the changelog correctly and the bug causes leaking unmovable
> > allocations into movable zones?
> 
> Hi Michal,
> 
> This bug will cause uninitialized migratetype, you can see from
> "cat /proc/pagetypeinfo", almost half blocks are Unmovable.

Please add that information to the changelog. Leaking unmovable
allocations to the movable zones defeats the whole purpose of the
movable zone so I guess we really want to mark this for stable.
AFAICS it should also note:
Fixes: ac5d2539b238 ("mm: meminit: reduce number of times pageblocks are set during struct page init")
and stable 4.2+

-- 
Michal Hocko
SUSE Labs