linux-kernel - Re: [PATCH v2 2/8] mm/isolation: remove unstable check for isolated page

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Date:	Fri, 8 Aug 2014 15:22:07 +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>, 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 v2 2/8] mm/isolation: remove unstable check for isolated
 page

On Thu, Aug 07, 2014 at 03:49:17PM +0200, Vlastimil Babka wrote:
> On 08/06/2014 09:18 AM, Joonsoo Kim wrote:
> >The check '!PageBuddy(page) && page_count(page) == 0 &&
> >migratetype == MIGRATE_ISOLATE' would mean the page on free processing.
> 
> What is "the page on free processing"? I thought this test means the
> page is on some CPU's pcplist?

Yes, you are right.

> 
> >Although it could go into buddy allocator within a short time,
> >futher operation such as isolate_freepages_range() in CMA, called after
> >test_page_isolated_in_pageblock(), could be failed due to this unstability
> 
> By "unstability" you mean the page can be allocated again from the
> pcplist instead of being freed to buddy list?

Yes.

> >since it requires that the page is on buddy. I think that removing
> >this unstability is good thing.
> >
> >And, following patch makes isolated freepage has new status matched with
> >this condition and this check is the obstacle to that change. So remove
> >it.
> 
> You could also say that pages from isolated pageblocks can no longer
> appear on pcplists after the later patches.

Okay. I will do it.

Thanks.
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