list_lru operation for new child memcg?

[Dave Airlie]

On Wed, 28 May 2025 at 17:20, Christian König <christian.koenig at amd.com> wrote:
>
> Hi guys,
>
> On 5/27/25 01:49, Dave Chinner wrote:
> > I disagree - specifically ordered memcg traversal is not something
> > that the list_lru implementation is currently doing, nor should it
> > be doing.
>
> I realized over night that I didn't fully explored a way of getting both advantages. And we actually don't need list_lru for that.
>
> So here is a side question:
>
> Is it possible to just have a per cgroup counter on how many pages a cgroup released back to a particular pool? E.g. something which is added up to the same counter on the parent when a cgroup is released.
>
> Background is that the pages are not distinguishable from each other, e.g. they are not cache hot or cold or anything like this. So it doesn't matter which pages a cgroup has released but only how many.
>
> If it would be possible to get such a counter then it would be like just a few lines of code to add the isolation and still get the advantage of sharing released pages between different cgroups.

I think numa is the only possible distinction I can see between pages
here, even uncached GPU access will be slower to further away numa
nodes,

But indeed this might be a workable idea, just make something that
does what list_lru does but just for the counters, and keep the pages
in a single pool.

Dave.