On 08/17/2012 11:02 AM, Michal Hocko wrote:

On Thu 09-08-12 17:01:16, Glauber Costa wrote:

quoted

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.

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