On 10/11/2012 05:11 PM, Michal Hocko wrote:

On Mon 08-10-12 14:06:15, Glauber Costa wrote:

quoted

Because kmem charges can outlive the cgroup, we need to make sure that
we won't free the memcg structure while charges are still in flight.
For reviewing simplicity, the charge functions will issue
mem_cgroup_get() at every charge, and mem_cgroup_put() at every
uncharge.

This can get expensive, however, and we can do better. mem_cgroup_get()
only really needs to be issued once: when the first limit is set. In the
same spirit, we only need to issue mem_cgroup_put() when the last charge
is gone.

We'll need an extra bit in kmem_accounted for that: KMEM_ACCOUNTED_DEAD.
it will be set when the cgroup dies, if there are charges in the group.
If there aren't, we can proceed right away.

Our uncharge function will have to test that bit every time the charges
drop to 0. Because that is not the likely output of
res_counter_uncharge, this should not impose a big hit on us: it is
certainly much better than a reference count decrease at every
operation.

[ v3: merged all lifecycle related patches in one ]

Signed-off-by: Glauber Costa <redacted>
CC: Kamezawa Hiroyuki <redacted>
CC: Christoph Lameter <redacted>
CC: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
CC: Michal Hocko <redacted>
CC: Johannes Weiner <redacted>
CC: Suleiman Souhlal <redacted>

OK, I like the optimization. I have just one comment to the
memcg_kmem_dead naming but other than that

Acked-by: Michal Hocko <redacted>

[...]

quoted

+static bool memcg_kmem_dead(struct mem_cgroup *memcg)

The name is tricky because it doesn't tell you that it clears the flag
which made me scratch my head when reading comment in kmem_cgroup_destroy

memcg_kmem_finally_kill_that_bastard() ?