On Mon 21-09-20 18:55:40, Yafang Shao wrote:

On Mon, Sep 21, 2020 at 4:12 PM Michal Hocko [off-list ref] wrote:

quoted

On Mon 21-09-20 16:02:55, zangchunxin@bytedance.com wrote:

quoted

From: Chunxin Zang <redacted>

In the cgroup v1, we have 'force_mepty' interface. This is very
useful for userspace to actively release memory. But the cgroup
v2 does not.

This patch reuse cgroup v1's function, but have a new name for
the interface. Because I think 'drop_cache' may be is easier to
understand :)

This should really explain a usecase. Global drop_caches is a terrible
interface and it has caused many problems in the past. People have
learned to use it as a remedy to any problem they might see and cause
other problems without realizing that. This is the reason why we even
log each attempt to drop caches.

I would rather not repeat the same mistake on the memcg level unless
there is a very strong reason for it.

I think we'd better add these comments above the function
mem_cgroup_force_empty() to explain why we don't want to expose this
interface in cgroup2, otherwise people will continue to send this
proposal without any strong reason.

I do not mind people sending this proposal.  "V1 used to have an
interface, we need it in v2 as well" is not really viable without
providing more reasoning on the specific usecase.

_Any_ patch should have a proper justification. This is nothing really
new to the process and I am wondering why this is coming as a surprise.

-- 
Michal Hocko
SUSE Labs