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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