linux-kernel - Re: [PATCH 00/10] fix freepage count problems due to memory isolation

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Date:	Thu, 17 Jul 2014 11:14:24 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
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, Lisa Du <cldu@...vell.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/10] fix freepage count problems due to memory isolation

On 07/17/2014 08:12 AM, Joonsoo Kim wrote:
>>
>> Hm I see. So what if it wasn't a special pcplist, but a special "free list"
>> where the pages would be just linked together as on pcplist, regardless of
>> order, and would not merge until the CPU that drives the memory isolation
>> process decides it is safe to flush them away. That would remove the need for
>> IPI's and provide the same guarantees I think.
>
> Looks good. It would work. I think that your solution is better than mine.
> I will implement it and test.

Thanks. But maybe there's still a good use for marking pages specially 
as isolated, and not PageBuddy with freepage_migratetype set to 
MIGRATE_ISOLATE. Why do we buddy-merge them anyway? I don't think CMA or 
memory offlining benefits from that, and it only makes the code more 
complex?
So maybe we could split isolated buddy pages to order-0 marked as 
PageIsolated and have a single per-zone list instead of order-based 
freelists?

>> Do we really need to check PageBuddy()? Could a page get marked as PageIsolate()
>> but still go to normal list instead of isolate list?
>
> Checking PageBuddy() is used for identifying page linked in normal
> list.

Ah right, forgot it walks by pfn scanning, not by traversing the free list.

> Thanks.
>
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