On 07/17/2015 10:13 AM, Michal Hocko wrote: > 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? In my particular case I'm interested in playing with the contents of /proc/meminfo, so that processes running inside a cgroup only see the the system as defined by the memcg restrictions -- 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
