Re: [External] Re: [PATCH] mm/memcontrol: Add the drop_cache interface for cgroup v2

From: Chunxin Zang
Date: Tue Sep 22 2020 - 06:24:50 EST

On Tue, Sep 22, 2020 at 5:51 PM Chris Down <chris@xxxxxxxxxxxxxx> wrote:
> Chunxin Zang writes:
> >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.
> This sounds like a perfect use case for memory.low on Type_A, and it's pretty
> much exactly what we invented it for. What's the problem with that?

But we cannot estimate how much memory Type_A uses at least.
For example:
total memory: 100G
At the beginning, Type_A was in an idle state, and it only used 10G of memory.
The load is very low. We want to run Type_B to avoid wasting machine resources.
When Type_B runs for a while, it used 80G of memory.
At this time Type_A is busy, it needs more memory.

Usually we will reclaim the memory of B first for Type_A . If not
enough, we will
kill Type_B.