Re: [PATCH] mm: memcontrol: prevent starvation when writing memory.high

[Johannes Weiner]

On Tue, Jan 12, 2021 at 10:59:58AM -0800, Shakeel Butt wrote:
> On Tue, Jan 12, 2021 at 9:12 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> >
> > When a value is written to a cgroup's memory.high control file, the
> > write() context first tries to reclaim the cgroup to size before
> > putting the limit in place for the workload. Concurrent charges from
> > the workload can keep such a write() looping in reclaim indefinitely.
> >
> 
> Is this observed on real workload?

Yes.

On several production hosts running a particularly aggressive
workload, we've observed writers to memory.high getting stuck for
minutes while consuming significant amount of CPU.

> Any particular reason to remove !reclaimed?

It's purpose so far was to allow successful reclaim to continue
indefinitely, while restricting no-progress loops to 'nr_retries'.

Without the first part, it doesn't really matter whether reclaim is
making progress or not: we do a maximum of 'nr_retries' loops until
the cgroup size meets the new limit, then exit one way or another.