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From: Greg Thelen <gthelen@google.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Young <hidave.darkstar@gmail.com>,
        Andrea Righi <arighi@develer.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Wu Fengguang <fengguang.wu@intel.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [patch 1/4] memcg: use native word to represent dirtyable pages
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Date: Mon, 08 Nov 2010 14:25:15 -0800
In-Reply-To: <AANLkTi=qO84k-KWaG2R_nQr7vxRA2E7DbO4=XhVrFzjv@mail.gmail.com>
	(Minchan Kim's message of "Mon, 8 Nov 2010 07:56:43 +0900")
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Minchan Kim <minchan.kim@gmail.com> writes:

> On Mon, Nov 8, 2010 at 7:14 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
>> The memory cgroup dirty info calculation currently uses a signed
>> 64-bit type to represent the amount of dirtyable memory in pages.
>>
>> This can instead be changed to an unsigned word, which will allow the
>> formula to function correctly with up to 160G of LRU pages on a 32-bit
Is is really 160G of LRU pages?  On 32-bit machine we use a 32 bit
unsigned page number.  With a 4KiB page size, I think that maps 16TiB
(1<<(32+12)) bytes.  Or is there some other limit?
>> system, assuming 4k pages.  That should be plenty even when taking
>> racy folding of the per-cpu counters into account.
>>
>> This fixes a compilation error on 32-bit systems as this code tries to
>> do 64-bit division.
>>
>> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
>> Reported-by: Dave Young <hidave.darkstar@gmail.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Greg Thelen <gthelen@google.com>