On Mon, Sep 21, 2020 at 7:05 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Mon 21-09-20 18:55:40, Yafang Shao wrote: > > On Mon, Sep 21, 2020 at 4:12 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > On Mon 21-09-20 16:02:55, zangchunxin@xxxxxxxxxxxxx wrote: > > > > From: Chunxin Zang <zangchunxin@xxxxxxxxxxxxx> > > > > > > > > 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. > I'm so sorry for that. My usecase is that there are two types of services in one server. They have difference priorities. Type_A has the highest priority, we need to ensure it's schedule latency、I/O latency、memory enough. Type_B has the lowest priority, we expect it will not affect Type_A when executed. So Type_A could use memory without any limit. Type_B could use memory only when the memory is absolutely sufficient. But we cannot estimate how much memory Type_B should use. Because everything is dynamic. So we can't set Type_B's memory.high. So we want to release the memory of Type_B when global memory is insufficient in order to ensure the quality of service of Type_A . In the past, we used the 'force_empty' interface of cgroup v1. > -- > Michal Hocko > SUSE Labs Best wishes Chunxin
