linux-kernel - Re: [PATCH 1/6] memcg: replace unsigned long by u64 to avoid overflow

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Date:	Mon, 25 Jun 2012 13:24:26 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Wanpeng Li <liwp.linux@...il.com>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Minchan Kim <minchan@...nel.org>,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/6] memcg: replace unsigned long by u64 to avoid overflow

(2012/06/23 18:26), Johannes Weiner wrote:
> On Sat, Jun 23, 2012 at 05:03:39PM +0800, Wanpeng Li wrote:
>> On Sat, Jun 23, 2012 at 10:15:14AM +0200, Johannes Weiner wrote:
>>> On Sat, Jun 23, 2012 at 02:15:34PM +0800, Wanpeng Li wrote:
>>>> From: Wanpeng Li <liwp@...ux.vnet.ibm.com>
>>>>
>>>> Since the return value variable in mem_cgroup_zone_nr_lru_pages and
>>>> mem_cgroup_node_nr_lru_pages functions are u64, so replace the return
>>>> value of funtions by u64 to avoid overflow.
>>>
>>> I wonder what 16 TB of memory must think running on a 32-bit kernel...
>>> "What is this, an address space for ants?"
>>
>> Hi Johannes,
>>
>> You mean change all u64 in memcg to unsigned long? or something I
>> miss....
>
> Not _all_ of them, we have some that count bytes.  But those counting
> pages should probably be ulong, yes.
>
> I think Kame added the ones that you wanted to adjust the surroundings
> for in particular, so let's ask him.  Kame?
>

I've been using 'unsigned long' for the number of pages and 'u64' for the number of
bytes. I think it's enough and it should be. I don't have any reason to use u64 for
the number of pages on 32bit archs.
If 'bytes' are handled by 'unsigned long', please fix it.

BTW, zone_page_state()::/include/linux/vmstat.h returns 'unsigned long'.
If you want to change this in memcg, please change zone's ones first.

Thanks,
-Kame

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