On 08/17/2012 02:35 PM, Michal Hocko wrote:

On Fri 17-08-12 14:07:00, Glauber Costa wrote:

quoted

On 08/17/2012 01:35 PM, Michal Hocko wrote:

quoted

quoted

quoted

Above you said "Once enabled, can't be disabled." and now you can

quoted

quoted

disable it? Say you are a leaf group with non accounted parents. This
will clear the flag and so no further accounting is done. Shouldn't
unlimited mean that we will never reach the limit? Or am I missing
something?

You are missing something, and maybe I should be more clear about that.
The static branches can't be disabled (it is only safe to disable them
from disarm_static_branches(), when all references are gone). Note that
when unlimited, we flip bits, do a transversal, but there is no mention
to the static branch.

My little brain still doesn't get this. I wasn't concerned about static
branches. I was worried about memcg_can_account_kmem which will return
false now, doesn't it.

Yes, it will. If I got you right, you are concerned because I said that
can't happen. But it will.

But I never said that can't happen. I said (ok, I meant) the static
branches can't be disabled.

Ok, then I misunderstood that because the comment was there even before
static branches were introduced and it made sense to me. This is
inconsistent with what we do for user accounting because even if we set
limit to unlimitted we still account. Why should we differ here?

There is another thing as well. Mel was right in his comment: I am
actually abusing this bit (because it is flippable), and it seems the
static branch can be updated more than once...

I'll merge your comments, and fix this.