Re: [patch 1/4] memcg: use native word to represent dirtyable pages

[Greg Thelen]

On Mon, Nov 8, 2010 at 2:38 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> On Mon, Nov 08, 2010 at 02:25:15PM -0800, Greg Thelen wrote:
>> Minchan Kim <minchan.kim@xxxxxxxxx> writes:
>>
>> > On Mon, Nov 8, 2010 at 7:14 AM, Johannes Weiner <hannes@xxxxxxxxxxx> 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.

Duh :)   thanks.
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