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

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Date:	Mon, 8 Nov 2010 14:43:11 -0800
From:	Greg Thelen <gthelen@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	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

On Mon, Nov 8, 2010 at 2:38 PM, Johannes Weiner <hannes@...xchg.org> wrote:
> On Mon, Nov 08, 2010 at 02:25:15PM -0800, Greg Thelen wrote:
>> 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?
>
> Yes, the dirty limit we calculate from it :)
>
> We have to be able to multiply this number by up to 100 (maximum dirty
> ratio value) without overflowing.

Duh :)   thanks.
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