On Tue 26-06-12 20:37:16, Glauber Costa wrote: > On 06/26/2012 08:15 PM, Michal Hocko wrote: > >On Tue 26-06-12 19:47:14, Glauber Costa wrote: > >>Okay, so after recent discussions, I am proposing the following > >>patch. It won't remove hierarchy, or anything like that. Just default > >>to true in the root cgroup, and print a warning once if you try > >>to set it back to 0. > >> > >>I am not adding it to feature-removal-schedule.txt because I don't > >>view it as a consensus. Rather, changing the default would allow us > >>to give it a time around in the open, and see if people complain > >>and what we can learn about that. > >> > >>Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx> > >>Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > >>CC: Michal Hocko <mhocko@xxxxxxx> > >>CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > >>CC: Tejun Heo <tj@xxxxxxxxxx> > >>--- > >> mm/memcontrol.c | 5 +++++ > >> 1 file changed, 5 insertions(+) > >> > >>diff --git a/mm/memcontrol.c b/mm/memcontrol.c > >>index 85f7790..c37e4c1 100644 > >>--- a/mm/memcontrol.c > >>+++ b/mm/memcontrol.c > >>@@ -3993,6 +3993,10 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, > >> if (memcg->use_hierarchy == val) > >> goto out; > >> > >>+ WARN_ONCE(!parent_memcg && memcg->use_hierarchy, > > > >Do you have to test anything here at all? The test above will get you > >out without doing anything if you are not trying to change anything. > >The default is true so you have to be trying to disable it. > > > >If you omit !parent_memcg test as well you will get a bonus of the early > >warning even if somebody has cgconfig.conf like this: > > > > group a/b/c { > > memory { > > memory.use_hierarchy = 0; > > [...] > > } > > } > > > >which worked previously... > >True there is a risk of a "false warning" when somebody just tries to > >set disable hierarchy when it is (and never was) allowed but I do not > >think this is that bad. > > > Well, a false warning is not that bad. > It is better to be vocal. > > I will wait for Kame to put his comments, and I can resend with that change. OK, you can resend with Acked-by: Michal Hocko <mhocko@xxxxxxx> And thanks! I will try to push this into OpenSUSE kernels to have a wider audience for testing. I think that the approach is safe because there is a safe fallback I mentioned earlier (maybe you can put it into the changelog) and if there really exists a setting which cannot be converted to non-hierarchical layout then we should better know as soon as possible. -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html