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Date: Thu, 7 Aug 2014 17:23:53 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>,
        Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan@kernel.org>,
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        "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
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        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/8] mm/page_alloc: fix pcp high, batch management
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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.