Re: [PATCH v2 2/5] memcg: provide root figures from system totals

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2013/03/13 18:59), Sha Zhengju wrote:
> On Wed, Mar 13, 2013 at 5:15 PM, Kamezawa Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>> (2013/03/13 15:58), Sha Zhengju wrote:
>>>
>>> On Wed, Mar 6, 2013 at 6:59 PM, Kamezawa Hiroyuki
>>> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>>>>
>>>> (2013/03/06 19:52), Glauber Costa wrote:
>>>>>
>>>>> On 03/06/2013 02:45 PM, Kamezawa Hiroyuki wrote:
>>>>>>
>>>>>> (2013/03/06 17:30), Glauber Costa wrote:
>>>>>>>
>>>>>>> On 03/06/2013 04:27 AM, Kamezawa Hiroyuki wrote:
>>>>>>>>
>>>>>>>> (2013/03/05 22:10), Glauber Costa wrote:
>>>>>>>>>
>>>>>>>>> + case _MEMSWAP: {
>>>>>>>>> +         struct sysinfo i;
>>>>>>>>> +         si_swapinfo(&i);
>>>>>>>>> +
>>>>>>>>> +         return ((memcg_read_root_rss() +
>>>>>>>>> +         atomic_long_read(&vm_stat[NR_FILE_PAGES])) << PAGE_SHIFT)
>>>>>>>>> +
>>>>>>>>> +         i.totalswap - i.freeswap;
>>>>>>>>
>>>>>>>>
>>>>>>>> How swapcache is handled ? ...and How kmem works with this calc ?
>>>>>>>>
>>>>>>> I am ignoring kmem, because we don't account kmem for the root cgroup
>>>>>>> anyway.
>>>>>>>
>>>>>>> Setting the limit is invalid, and we don't account until the limit is
>>>>>>> set. Then it will be 0, always.
>>>>>>>
>>>>>>> For swapcache, I am hoping that totalswap - freeswap will cover
>>>>>>> everything swap related. If you think I am wrong, please enlighten me.
>>>>>>>
>>>>>>
>>>>>> i.totalswap - i.freeswap = # of used swap entries.
>>>>>>
>>>>>> SwapCache can be rss and used swap entry at the same time.
>>>>>>
>>>>>
>>>>> Well, yes, but the rss entries would be accounted for in get_mm_rss(),
>>>>> won't they ?
>>>>>
>>>>> What am I missing ?
>>>>
>>>>
>>>>
>>>> I think the correct caluculation is
>>>>
>>>>     Sum of all RSS + All file caches + (i.total_swap - i.freeswap - # of
>>>> mapped SwapCache)
>>>>
>>>>
>>>> In the patch, mapped SwapCache is counted as both of rss and swap.
>>>>
>>>
>>> After a quick look, swapcache is counted as file pages and meanwhile
>>> use a swap entry at the same time(__add_to{delete_from}_swap_cache()).
>>> Even though, I think we still do not need to exclude swapcache out,
>>> because it indeed uses two copy of resource: one is swap entry, one is
>>> cache, so the usage should count both of them in.
>>>
>>> What I think it matters is that swapcache may be counted as both file
>>> pages and rss(if it's a process's anonymous page), which we need to
>>> subtract # of swapcache to avoid double-counting. But it isn't always
>>> so: a shmem/tmpfs page may use swapcache and be counted as file pages
>>> but not a rss, then we can not subtract swapcache... Is there anything
>>> I lost?
>>>
>>
>>
>> Please don't think difficult. All pages for user/caches are counted in
>> LRU. All swap-entry usage can be cauht by total_swap_pages - nr_swap_pages.
>> We just need to subtract number of swap-cache which is double counted
>> as swap-entry and a page in LRU.
>>
>> NR_ACTIVE_ANON + NR_INACTIVE_ANON + NR_ACTIVE_FILE + NR_INACTIVE_FILE
>> + NR_UNEVICTABLE + total_swap_pages - nr_swap_pages - NR_SWAP_CACHE
>>
>
> Using LRU numbers is more suitable. But forgive me, I still doubt
> whether we should subtract NR_SWAP_CACHE out because it uses both a
> swap entry and a page cache and it isn't a real double counting.
>

Used swap entry can be reclaimed if there are SwapCache on memory.

Thanks,
ーKame


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