linux-kernel - Re: [patch 1/4] memcg: use native word to represent dirtyable pages

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Message-ID: <xr93aaljbghg.fsf@ninji.mtv.corp.google.com>
Date:	Mon, 08 Nov 2010 14:25:15 -0800
From:	Greg Thelen <gthelen@...gle.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <hidave.darkstar@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] memcg: use native word to represent dirtyable pages

Minchan Kim <minchan.kim@...il.com> writes:

> On Mon, Nov 8, 2010 at 7:14 AM, Johannes Weiner <hannes@...xchg.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@...xchg.org>
>> Reported-by: Dave Young <hidave.darkstar@...il.com>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
Reviewed-by: Greg Thelen <gthelen@...gle.com>
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