linux-kernel - Re: [PATCH v2 3/8] mm/page_alloc: fix pcp high, batch management

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Date:	Thu, 7 Aug 2014 17:23:53 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Zhang Yanfei <zhangyanfei@...fujitsu.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>,
	"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 3/8] mm/page_alloc: fix pcp high, batch management

On Thu, Aug 07, 2014 at 10:11:14AM +0800, Zhang Yanfei wrote:
> Hi Joonsoo,
> 
> On 08/06/2014 03:18 PM, Joonsoo Kim wrote:
> > per cpu pages structure, aka pcp, has high and batch values to control
> > how many pages we perform caching. This values could be updated
> > asynchronously and updater should ensure that this doesn't make any
> > problem. For this purpose, pageset_update() is implemented and do some
> > memory synchronization. But, it turns out to be wrong when I implemented
> > new feature using this. There is no corresponding smp_rmb() in read-side
> 
> Out of curiosity, what new feature are you implementing?

I mean just zone_pcp_disable() and zone_pcp_enable(). :)

> IIRC, pageset_update() is used to update high and batch which can be changed
> during:
> 
> system boot
> sysfs
> memory hot-plug
> 
> So it seems to me that the latter two would have the problems you described here.

Yes, I think so. But I'm not sure, because I didn't look at it
in detail. :)

Thanks.

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