[Devel] Re: [PATCH v2 08/11] memcg: disable kmem code when not in use.

[Glauber Costa]

On 08/17/2012 11:02 AM, Michal Hocko wrote:
> On Thu 09-08-12 17:01:16, Glauber Costa wrote:
>> We can use jump labels to patch the code in or out when not used.
>>
>> Because the assignment: memcg->kmem_accounted = true is done after the
>> jump labels increment, we guarantee that the root memcg will always be
>> selected until all call sites are patched (see memcg_kmem_enabled).
> 
> Not that it would be really important because kmem_accounted goes away
> in a subsequent patch but I think the wording is a bit misleading here.
> First of all there is no guanratee that kmem_accounted=true is seen
> before atomic_inc(&key->enabled) because there is no memory barrier and
> the lock serves just a leave barrier. But I do not think this is
> important at all because key->enabled is what matters here. Even if
> memcg_kmem_enabled is true we do not consider it if the key is disabled,
> right?
> 

Right.