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Date:	Mon, 14 Jul 2014 15:24:23 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Ritesh Harjani <ritesh.list@...il.com>,
	t.stanislaws@...sung.com, Gioh Kim <gioh.kim@....com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/10] mm/page_alloc: handle page on pcp correctly if
 it's pageblock is isolated

On Mon, Jul 07, 2014 at 05:19:48PM +0200, Vlastimil Babka wrote:
> On 07/04/2014 09:57 AM, Joonsoo Kim wrote:
> >If pageblock of page on pcp are isolated now, we should free it to isolate
> >buddy list to prevent future allocation on it. But current code doesn't
> >do this.
> >
> >Moreover, there is a freepage counting problem on current code. Although
> >pageblock of page on pcp are isolated now, it could go normal buddy list,
> >because get_onpcp_migratetype() will return non-isolate migratetype.
> 
> get_onpcp_migratetype() is only introduced in later patch.

Yes, I will fix it.

> 
> >In this case, we should do either adding freepage count or changing
> >migratetype to MIGRATE_ISOLATE, but, current code do neither.
> 
> I wouldn't say it "do neither". It already limits the freepage
> counting to !MIGRATE_ISOLATE case (and it's not converted to
> __mod_zone_freepage_state for some reason). So there's accounting
> mismatch in addition to buddy list misplacement.

Okay.

> 
> >This patch fixes these two problems by handling pageblock migratetype
> >before calling __free_one_page(). And, if we find the page on isolated
> >pageblock, change migratetype to MIGRATE_ISOLATE to prevent future
> >allocation of this page and freepage counting problem.
> 
> So although this is not an addition of a new pageblock migratetype
> check to the fast path (the check is already there), I would prefer
> removing the check :) 

Yes, I want to do it if possible. :)

> With the approach of pcplists draining
> outlined in my reply to 00/10, we would allow a misplacement to
> happen (and the page accounted as freepage) immediately followed by
> move_frepages_block which would place the page onto isolate freelist
> with the rest. Anything newly freed will get isolate_migratetype
> determined in free_hot_cold_page or __free_pages_ok (where it would
> need moving the migratepage check under the disabled irq part) and
> be placed and buddy-merged properly.

I explained the problem of this approach in 00/10.

Thanks.

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