Messages in this thread |  | | Date | Tue, 11 Dec 2012 14:36:10 -0800 | Subject | Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup iterators | From | Ying Han <> |
| |
On Tue, Dec 11, 2012 at 7:54 AM, Michal Hocko <mhocko@suse.cz> wrote: > On Sun 09-12-12 11:39:50, Ying Han wrote: >> On Mon, Nov 26, 2012 at 10:47 AM, Michal Hocko <mhocko@suse.cz> wrote: > [...] >> > if (reclaim) { >> > - iter->position = id; >> > + struct mem_cgroup *curr = memcg; >> > + >> > + if (last_visited) >> > + css_put(&last_visited->css); > ^^^^^^^^^^^ > here >> > + >> > + if (css && !memcg) >> > + curr = mem_cgroup_from_css(css); >> > + >> > + /* make sure that the cached memcg is not removed */ >> > + if (curr) >> > + css_get(&curr->css); >> > + iter->last_visited = curr; >> >> Here we take extra refcnt for last_visited, and assume it is under >> target reclaim which then calls mem_cgroup_iter_break() and we leaked >> a refcnt of the target memcg css. > > I think you are not right here. The extra reference is kept for > iter->last_visited and it will be dropped the next time somebody sees > the same zone-priority iter. See above. > > Or have I missed your question?
Hmm, question remains.
My understanding of the mem_cgroup_iter() is that each call path should close the loop itself, in the sense that no *leaked* css refcnt after that loop finished. It is the case for all the caller today where the loop terminates at memcg == NULL, where all the refcnt have been dropped by then.
One exception is mem_cgroup_iter_break(), where the loop terminates with *leaked* refcnt and that is what the iter_break() needs to clean up. We can not rely on the next caller of the loop since it might never happen.
It makes sense to drop the refcnt of last_visited, the same reason as drop refcnt of prev. I don't see why it makes different.
--Ying
> > [...] > -- > Michal Hocko > SUSE Labs
|  |