On Fri, Jul 10, 2015 at 02:45:20PM +0200, Michal Hocko wrote: > On Fri 10-07-15 10:54:00, Vladimir Davydov wrote: > > On Thu, Jul 09, 2015 at 04:09:41PM +0200, Michal Hocko wrote: > > > On Wed 08-07-15 20:32:51, Vladimir Davydov wrote: > > > > On Wed, Jul 08, 2015 at 02:27:51PM +0200, Michal Hocko wrote: > > [...] > > > > > @@ -474,7 +519,7 @@ static inline void mem_cgroup_count_vm_event(struct mm_struct *mm, > > > > > return; > > > > > > > > > > rcu_read_lock(); > > > > > - memcg = mem_cgroup_from_task(rcu_dereference(mm->owner)); > > > > > + memcg = rcu_dereference(mm->memcg); > > > > > if (unlikely(!memcg)) > > > > > goto out; > > > > > > > > > > > > > If I'm not mistaken, mm->memcg equals NULL for any task in the root > > > > memory cgroup > > > > > > right > > > > > > > (BTW, it it's true, it's worth mentioning in the comment > > > > to mm->memcg definition IMO). As a result, we won't account the stats > > > > for such tasks, will we? > > > > > > well spotted! This is certainly a bug. There are more places which are > > > checking for mm->memcg being NULL and falling back to root_mem_cgroup. I > > > think it would be better to simply use root_mem_cgroup right away. We > > > can setup init_mm.memcg = root_mem_cgroup during initialization and be > > > done with it. What do you think? The diff is in the very end of the > > > email (completely untested yet). > > > > I'd prefer initializing init_mm.memcg to root_mem_cgroup. This way we > > wouldn't have to check whether mm->memcg is NULL or not here and there, > > which would make the code cleaner IMO. > > So the patch I've posted will not work as a simple boot test told me. We > are initializing root_mem_cgroup too late. This will be more complicated. > I will leave this idea outside of this patch series and will come up > with a separate patch which will clean this up later. I will update the > doc discouraging any use of mm->memcg outside of memcg and use accessor > functions instead. There is only one currently (mm/debug.c) and this is > used only to print the pointer which is safe. Why can't we make root_mem_cgroup statically allocated? AFAICS it's a common practice - e.g. see blkcg_root, root_task_group. Thanks, Vladimir -- 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>