Re: [RFC 0/4] Introduce unbalance proactive reclaim

[Yosry Ahmed]

+Wei Xu +David Rientjes

On Tue, Nov 7, 2023 at 10:59 PM Huan Yang <link@xxxxxxxx> wrote:
>
> In some cases, we need to selectively reclaim file pages or anonymous
> pages in an unbalanced manner.
>
> For example, when an application is pushed to the background and frozen,
> it may not be opened for a long time, and we can safely reclaim the
> application's anonymous pages, but we do not want to touch the file pages.
>
> This patchset extends the proactive reclaim interface to achieve
> unbalanced reclamation. Users can control the reclamation tendency by
> inputting swappiness under the original interface. Specifically, users
> can input special values to extremely reclaim specific pages.

I proposed this a while back:

https://lore.kernel.org/linux-mm/CAJD7tkbDpyoODveCsnaqBBMZEkDvshXJmNdbk51yKSNgD7aGdg@xxxxxxxxxxxxxx/

The takeaway from the discussion was that swappiness is not the right
way to do this. We can add separate arguments to specify types of
memory to reclaim, as Roman suggested in that thread. I had some
patches lying around to do that at some point, I can dig them up if
that's helpful, but they are probably based on a very old kernel now,
and before MGLRU landed. IIRC it wasn't very difficult, I think I
added anon/file/shrinkers bits to struct scan_control and then plumbed
them through to memory.reclaim.

>
> Example:
>         echo "1G" 200 > memory.reclaim (only reclaim anon)
>           echo "1G" 0  > memory.reclaim (only reclaim file)
>           echo "1G" 1  > memory.reclaim (only reclaim file)

The type of interface here is nested-keyed, so if we add arguments
they need to be in key=value format. Example:

echo 1G swappiness=200 > memory.reclaim

As I mentioned above though, I don't think swappiness is the right way
of doing this. Also, without swappiness, I don't think there's a v1 vs
v2 dilemma here. memory.reclaim can work as-is in cgroup v1, it just
needs to be exposed there.