Date: Mon, 8 Nov 2010 23:38:38 +0100
From: Johannes Weiner <hannes@cmpxchg.org>
To: Greg Thelen <gthelen@google.com>
Cc: Minchan Kim <minchan.kim@gmail.com>,
        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
Message-ID: <20101108223838.GM23393@cmpxchg.org>
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 <20101107215030.007259800@cmpxchg.org>
 <20101107220353.115646194@cmpxchg.org>
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On Mon, Nov 08, 2010 at 02:25:15PM -0800, Greg Thelen wrote:
> 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?

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.
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