On Fri 12-10-12 11:47:17, Glauber Costa wrote: > On 10/11/2012 05:11 PM, Michal Hocko wrote: > > On Mon 08-10-12 14:06:15, Glauber Costa wrote: > >> 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 <glommer@xxxxxxxxxxxxx> > >> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > >> CC: Christoph Lameter <cl@xxxxxxxxx> > >> CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > >> CC: Michal Hocko <mhocko@xxxxxxx> > >> CC: Johannes Weiner <hannes@xxxxxxxxxxx> > >> CC: Suleiman Souhlal <suleiman@xxxxxxxxxx> > > > > OK, I like the optimization. I have just one comment to the > > memcg_kmem_dead naming but other than that > > > > Acked-by: Michal Hocko <mhocko@xxxxxxx> > > > > [...] > >> +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() ? memcg_kmem_test_and_clear_dead? I know long but at least clear that the flag is cleared. Or just open code it. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>