Re: memcg Can't context between v1 and v2 because css->refcnt not released

[Michal Hocko <mhocko@kernel.org>]

On Wed 09-08-17 15:06:34, wang Yu wrote:
> Hello Johannes ,Michal,and Tejun:
> 
>   i using memcg v1,  but some reason  i want to context to  memcg v2,
> but i can't, here is my step:
> #cat /proc/cgroups
> #subsys_name hierarchy num_cgroups enabled
>  memory 5 1 1
> #cd /sys/fs/cgroup/memory
> #mkdir a
> #echo 0 > a/cgroup.procs
> #sleep 1
> #echo 0 > cgroup.procs

This doesn't do what you think. It will try to add a non-existant pid 0
to the root cgroup. You need to remove cgroup a. Moreover it is possible
that the `sleep' command will fault some page cache and that will stay
in memcg `a' until there is a memory pressure. cgroup v1 had
force_empty knob which you can use to drain the cgroup before removal.
Then you should be able to umount the v1 cgroup and mount v2.
-- 
Michal Hocko
SUSE Labs

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