On Fri 17-07-15 00:21:51, Nikolay Borisov wrote: > On Thu, Jul 16, 2015 at 6:22 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Thu 16-07-15 18:11:48, Nikolay Borisov wrote: > >> > >> > >> On 07/16/2015 05:59 PM, Michal Hocko wrote: > >> > On Thu 16-07-15 16:34:08, Nikolay Borisov wrote: > >> >> Hello, > >> >> > >> >> I'd like to ask what are the locking rules when using > >> >> mem_cgroup_from_task(current)? Currently I'm doing this under > >> >> rcu_read_lock which I believe is sufficient. However, I've seen patches > >> >> where reference is obtained via mem_cgroup_from_task and then > >> >> css_tryget_online is used on the resulting cgroup? > >> > > >> > RCU will guarantee that the memcg will not go away. The rest depends on > >> > what you want to do with it. If you want to use it outside of RCU you > >> > have to take a reference. And then it depends what the memcg is used > >> > for - some operations can be done also on the offline memcg. > >> > > >> > Btw. mem_cgroup_from_task is not the proper interface for you. You > >> > really want to do > >> > memcg = get_mem_cgroup_from_mm(current->mm) > >> > [...] > >> > css_put(&memcg) > >> > >> Unfortunately this function is static, do you think there might be any > >> value of a patch that exposes it upstream? > > > > Ohh, you are right! I thought I made it visible with my recent changes > > but nope. There are no external users currently. > > > > Could you tell us more why it would be useful for you? > > In my particular use case I have to query the memcg's various counters to expose > them to the user in a different way than via the cgroup files > (memory.limit_in_bytes etc). Why is the regular interface not sufficient? -- Michal Hocko SUSE Labs -- 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
