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

[wang Yu <yuwang668899@gmail.com>]

at first ,thanks for your reply.
but i also tested what you said, the problem is also.
force_empty only call try_to_free_pages, not all the pages remove
because mem_cgroup_reparent_charges moved
#cd /sys/fs/cgroup/memory
#mkdir a
#echo 0 > a/cgroup.procs
#sleep 1
#echo 0 > a/cgroup.procs
#echo 1 > a/memory.force_empty
#rmdir a
#cat /proc/cgroups
#subsys_name hierarchy num_cgroups enabled
memory 2 2 1
the num_cgroups also not released





2017-08-10 15:10 GMT+08:00 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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