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SubjectRe: [PATCH 6/7] memcg: add per cgroup writeback pages accounting
(2012/07/09 13:14), Fengguang Wu wrote:
> On Mon, Jul 09, 2012 at 11:36:11AM +0800, Sha Zhengju wrote:
>> On 07/08/2012 10:53 PM, Fengguang Wu wrote:
>>>> @@ -2245,7 +2252,10 @@ int test_set_page_writeback(struct page *page)
>>>> {
>>>> struct address_space *mapping = page_mapping(page);
>>>> int ret;
>>>> + bool locked;
>>>> + unsigned long flags;
>>>>
>>>> + mem_cgroup_begin_update_page_stat(page,&locked,&flags);
>>>> if (mapping) {
>>>> struct backing_dev_info *bdi = mapping->backing_dev_info;
>>>> unsigned long flags;
>>>> @@ -2272,6 +2282,8 @@ int test_set_page_writeback(struct page *page)
>>>> }
>>>> if (!ret)
>>>> account_page_writeback(page);
>>>> +
>>>> + mem_cgroup_end_update_page_stat(page,&locked,&flags);
>>>> return ret;
>>>>
>>>> }
>>> Where is the MEM_CGROUP_STAT_FILE_WRITEBACK increased?
>>>
>>
>> It's in account_page_writeback().
>>
>> void account_page_writeback(struct page *page)
>> {
>> + mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_FILE_WRITEBACK);
>> inc_zone_page_state(page, NR_WRITEBACK);
>> }
>
> I didn't find that chunk, perhaps it's lost due to rebase..
>
>> There isn't a unified interface to dec/inc writeback accounting, so
>> I just follow that.
>> Maybe we can rework account_page_writeback() to also account
>> dec in?
>
> The current seperate inc/dec paths are fine. It sounds like
> over-engineering if going any further.
>
> I'm a bit worried about some 3rd party kernel module to call
> account_page_writeback() without mem_cgroup_begin/end_update_page_stat().
> Will that lead to serious locking issues, or merely inaccurate
> accounting?
>

Ah, Hm. Maybe it's better to add some debug check in
mem_cgroup_update_page_stat(). rcu_read_lock_held() or some.

Thanks,
-Kame





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