Re: [PATCH 0/7] kernel/cgroups: Add "dev" memory accounting cgroup.

[Maxime Ripard <mripard@kernel.org>]

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Hi Tejun,

Thanks a lot for your review.

On Wed, Oct 23, 2024 at 09:40:28AM -1000, Tejun Heo wrote:
> On Wed, Oct 23, 2024 at 09:52:53AM +0200, Maarten Lankhorst wrote:
> > New submission!
> > I've added documentation for each call, and integrated the renaming from
> > drm cgroup to dev cgroup, based on maxime ripard's work.
> > 
> > Maxime has been testing this with dma-buf heaps and v4l2 too, and it seems to work.
> > In the initial submission, I've decided to only add the smallest enablement possible,
> > to have less chance of breaking things.
> > 
> > The API has been changed slightly, from "$name region.$regionname=$limit" in a file called
> > dev.min/low/max to "$subsystem/$name $regionname=$limit" in a file called dev.region.min/low/max.
> > 
> > This hopefully allows us to perhaps extend the API later on with the possibility to
> > set scheduler weights on the device, like in
> > 
> > https://blogs.igalia.com/tursulin/drm-scheduling-cgroup-controller/
> > 
> > Maarten Lankhorst (5):
> >   kernel/cgroup: Add "dev" memory accounting cgroup
> 
> Yeah, let's not use "dev" name for this. As Waiman pointed out, it conflicts
> with the devices controller from cgroup1. While cgroup1 is mostly
> deprecated, the same features are provided through BPF in systemd using the
> same terminologies, so this is going to be really confusing.

Yeah, I agree. We switched to dev because we want to support more than
just DRM, but all DMA-able memory. We have patches to support for v4l2
and dma-buf heaps, so using the name DRM didn't feel great either.

Do you have a better name in mind? "device memory"? "dma memory"?

> What happened with Tvrtko's weighted implementation? I've seen many proposed
> patchsets in this area but as far as I could see none could establish
> consensus among GPU crowd and that's one of the reasons why nothing ever
> landed. Is the aim of this patchset establishing such consensus?

Yeah, we have a consensus by now I think. Valve, Intel, Google, and Red
Hat have been involved in that series and we all agree on the implementation.

Tvrtko aims at a different feature set though: this one is about memory
allocation limits, Tvrtko's about scheduling.

Scheduling doesn't make much sense for things outside of DRM (and even
for a fraction of all DRM devices), and it's pretty much orthogonal. So
i guess you can expect another series from Tvrtko, but I don't think
they should be considered equivalent or dependent on each other.

> If reaching consensus doesn't seem feasible in a predictable timeframe, my
> suggesstion is just extending the misc controller. If the only way forward
> here is fragmented vendor(s)-specific implementations, let's throw them into
> the misc controller.

I don't think we have a fragmented implementation here, at all. The last
patch especially implements it for all devices implementing the GEM
interface in DRM, which would be around 100 drivers from various vendors.

It's marked as a discussion because we don't quite know how to plumb it
in for all drivers in the current DRM framework, but it's very much what
we want to achieve.

Maxime

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