Re: [PATCH 1/5 v2] memcg: replace unsigned long by u64 to avoid overflow

[Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>]

On 07/04/2012 04:24 PM, Wanpeng Li wrote:
> On Mon, Jun 25, 2012 at 05:30:11PM +0900, Kamezawa Hiroyuki wrote:
>> (2012/06/25 16:52), Johannes Weiner wrote:
>>> On Mon, Jun 25, 2012 at 02:04:20PM +0800, Wanpeng Li wrote:
>>>> Changlog:
>>>>
>>>> V2 -> V1:
>>>> * fix zone_page_state()::/include/linux/vmstat.h returns 'unsigned long'
>>>>
>>>> From: Wanpeng Li <liwp-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
>>>>
>>>> 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.
>>>>
>>>> Signed-off-by: Wanpeng Li <liwp.linux-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>>> ---
>>>>  include/linux/vmstat.h |    2 +-
>>>>  mm/memcontrol.c        |    5 ++---
>>>>  2 files changed, 3 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
>>>> index 65efb92..6a14291 100644
>>>> --- a/include/linux/vmstat.h
>>>> +++ b/include/linux/vmstat.h
>>>> @@ -106,7 +106,7 @@ static inline unsigned long global_page_state(enum zone_stat_item item)
>>>>  	return x;
>>>>  }
>>>>
>>>> -static inline unsigned long zone_page_state(struct zone *zone,
>>>> +static inline u64 zone_page_state(struct zone *zone,
>>>>  					enum zone_stat_item item)
>>>>  {
>>>>  	long x = atomic_long_read(&zone->vm_stat[item]);
>>>
>>> We established that there is no known reason to use ulong for page
>>> counters and that IF YOU HAD ONE, you should obviously say so and then
>>> do a wholesale conversion.  But I don't think you have one.
>>>
>>> This patch makes absolutely no sense.
>>>
>> I agree. Then, Nack from me.
>>
>> Thanks,
>> -Kame
> 
> static unsigned long
> mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
> 			int nid, unsigned int lru_mask)
> {
> 	u64 total = 0;
> 	int zid;
> 
> 	for (zid = 0; zid < MAX_NR_ZONES; zid++)
> 		total += mem_cgroup_zone_nr_lru_pages(memcg,
> 					    nid, zid, lru_mask);
> 
> 	return total;
> }
> 
> Since you use unsigned long to caculate nr_pages and unsigned long long
> to caculate bytes, so u64 in function mem_cgroup_node_nr_lru_pages should 
> replace by unsigned long to save kernel stack, right?

How many bytes do you intend to save by replacing "u64" with "unsigned
long" ? Have you asked yourself this question ?