linux-kernel - Re: [PATCH] memcg: use do_div to divide s64 in 32 bit machine.

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Date:	Sun, 7 Nov 2010 02:31:13 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	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 Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] memcg: use do_div to divide s64 in 32 bit machine.

On Sun, Nov 7, 2010 at 2:19 AM, Greg Thelen <gthelen@...gle.com> wrote:
> On Fri, Nov 5, 2010 at 6:03 PM,  <hannes@...xchg.org> wrote:
>> On Sat, Nov 06, 2010 at 01:08:53AM +0900, Minchan Kim wrote:
>>> Use do_div to divide s64 value. Otherwise, build would be failed
>>> like Dave Young reported.
>>
>> I thought about that too, but then I asked myself why you would want
>> to represent a number of pages as signed 64bit type, even on 32 bit?
>
> I think the reason that 64 byte type is used for page count in
> memcontrol.c is because the low level res_counter primitives operate
> on 64 bit counters, even on 32 bit machines.
>
>> Isn't the much better fix to get the types right instead?
>>
>
> I agree that consistent types between mem_cgroup_dirty_info() and
> global_dirty_info() is important.  There seems to be a lot of usage of
> s64 for page counts in memcontrol.c, which I think is due to the
> res_counter types.  I think these s64 be switched to unsigned long
> rather to be consistent with the rest of mm code.  It looks like this
> will be a clean patch, except for the lowest level where
> res_counter_read_u64() is used, where some casting may be needed.
>
> I'll post a patch for that change.
>

Agree. I don't mind it.
Thanks, Hannes and Greg.



-- 
Kind regards,
Minchan Kim
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