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

[Chris Down]

Chunxin Zang writes:
> 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.

memory.low allows ballparking, you don't have to know exactly how much it uses.  
Any amount of protection biases reclaim away from that cgroup.

> 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.

Ok, so set memory.low for Type_A close to your maximum expected value.