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

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Date:	Wed, 13 Aug 2014 17:19:21 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
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>,
	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 Mon, Aug 11, 2014 at 02:53:35PM +0530, Aneesh Kumar K.V wrote:
> Joonsoo Kim <iamjoonsoo.kim@....com> writes:
> 
> > The check '!PageBuddy(page) && page_count(page) == 0 &&
> > migratetype == MIGRATE_ISOLATE' would mean the page on free processing.
> > 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
> > since it requires that the page is on buddy. I think that removing
> > this unstability is good thing.
> 
> Is that true in case of check_pages_isolated_cb ? Does that require
> PageBuddy to be true ?

I think so.

> 
> >
> > 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.
> 
> Can you quote the patch summary in the above case ? ie, something like
> 
> And the followiing patch "mm/....." makes isolate freepage.
> 

Okay.

"mm/isolation: change pageblock isolation logic to fix freepage
counting bugs" introduce PageIsolated() and mark freepages
PageIsolated() during isolation. Those pages are !PageBuddy() and
page_count() == 0.

Thanks.
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