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

[Greg Thelen]

On Fri, Nov 5, 2010 at 6:03 PM,  <hannes@xxxxxxxxxxx> 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.
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