Re: [PATCH v2 2/6] memcg: bypass swap accounting for the root memcg

[Lord Glauber Costa of Sealand <glommer@parallels.com>]

On 01/28/2013 02:54 PM, Jeff Liu wrote:
> Root memcg with swap cgroup is special since we only do tracking but can
> not set limits against it.  In order to facilitate the implementation of
> the coming swap cgroup structures delay allocation mechanism, we can bypass
> the default swap statistics upon the root memcg and figure it out through
> the global stats instead as below:
> 
I am sorry if this is was already discussed before, but:
> root_memcg_swap_stat: total_swap_pages - nr_swap_pages - used_swap_pages_of_all_memcgs
> memcg_total_swap_stats: root_memcg_swap_stat + other_memcg_swap_stats
> 

Shouldn't it *at least* be dependent on use_hierarchy?

I don't see why root_memcg won't be always total_swap_pages -
nr_swap_pages, since the root memcg is always viewed as a superset of
the others, AFAIR.

Even if it is not the general case (which again, I really believe it
is), it certainly is the case for hierarchy enabled setups.

Also, I truly don't understand what is the business of
root_memcg_swap_stat in non-root memcgs.

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