Re: [PATCH] mm/mglru: fix cgroup OOM during MGLRU state switching

[Kairui Song <ryncsn@gmail.com>]

On Mon, Mar 2, 2026 at 5:20 PM Barry Song <21cnbao@gmail.com> wrote:
>
> On Mon, Mar 2, 2026 at 4:25 PM Yafang Shao <laoar.shao@gmail.com> wrote:
> >
> > The challenge we're currently facing is that we don't yet know which
> > workloads would benefit from it ;)
> > We do want to enable mglru on our production servers, but first we
> > need to address the risk of OOM during the switch—that's exactly why
> > we're proposing this patch.
>
> Nobody objects to your intention to fix it. I’m curious: to what
> extent do we want to fix it? Do we aim to merely reduce the probability
> of OOM and other mistakes, or do we want a complete fix that makes
> the dynamic on/off fully safe?

Yeah, I'm glad that more people are trying MGLRU and improving it.

We also have an downstream fix for the OOM on switch issue, but that's
mostly as a fallback in case MGLRU doesn't work well, our goal is
still try to enable MGLRU as much as possible, many issues have been
identified and I'm willing to push and fix things upstream together.

I didn't consider the the OOM on switch an upstream issue though. But
to fix that we just used a schedule_timeout when seeing the lru status
is different from the global status, very close to what Barry
suggested, with some other tweaks.

Keep doing the reclaim during the switch did result in some unexpected
behaviors, including OOM still occurring, just much more unlikely than
before. Like a typical TOCTOU problem for checking the lru's status.

Let me Cc BIngfang, maybe he can provide more detail.