Re: [LSF/MM/BPF TOPIC] Overhauling hot page detection and promotion based on PTE A bit scanning

[Raghavendra K T]

On 1/27/2025 12:31 PM, David Rientjes wrote:
> On Fri, 24 Jan 2025, Raghavendra K T wrote:
[...]
> > > By the way, do you have any reason why you'd prefer opt-in prctl
> > > over per-memcg control?
> >
> > opt-in prctl came in the MM alignment discussion, and have added that.
>
> Are you planning on sending a refresh of that patch series? :)

Hello David,
Current plan is to send by next week.
(Because after measuring the per mm latency and overall latency to do
full scan, I was thinking to add parallel scanning in next version itself).

> > per-memcg also definitely makes sense. I am not aware which is the most
> > used usecase. But adding provision for both with one having more
> > priority over other may be the way to go.
>
> I would suggest leveraging prctl() for this as opposed to memcg.  I think
> making this part of memcg is beyond the scope for what memcg is intended
> to do, limitation of memory resources, similar to the recent discussions
> on per-cgroup control for THP.
>
> Additionally, the current memcg configuration of the system may also not
> be convenient for using for this purpose, especially if one process should
> be opted out in the memcg hierarchy.  Requiring users to change how their
> memcg is configured just to opt out would be rather unfortunate.
>
> > Overall point here is to save time in unnecessary scanning.
> > will be adding prctl in the upcoming version to start with.
>
> Fully agreed.
>
> Thanks very much for proposing this topic, Raghu, I think it will be very
> useful to discuss!  Looking forward to it!

Thank you.

- Raghu