linux-kernel - Re: [PATCH v2 0/7] kernel/cgroups: Add "dmem" memory accounting cgroup.

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Message-ID: <20241217-meek-bullfinch-of-luck-2c3468@houat>
Date: Tue, 17 Dec 2024 08:46:10 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Maarten Lankhorst <dev@...khorst.se>
Cc: linux-kernel@...r.kernel.org, intel-xe@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>, 
	Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Friedrich Vock <friedrich.vock@....de>, cgroups@...r.kernel.org, linux-mm@...ck.org, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Subject: Re: [PATCH v2 0/7] kernel/cgroups: Add "dmem" memory accounting
 cgroup.

On Fri, Dec 13, 2024 at 05:06:05PM +0100, Maarten Lankhorst wrote:
> Hey,
> 
> Den 2024-12-13 kl. 16:21, skrev Maxime Ripard:
> > On Fri, Dec 13, 2024 at 03:53:13PM +0100, Maarten Lankhorst wrote:
> > > 
> > > 
> > > Den 2024-12-13 kl. 14:03, skrev Maxime Ripard:
> > > > Hi,
> > > > 
> > > > Thanks for the new update!
> > > > 
> > > > On Wed, Dec 04, 2024 at 02:44:00PM +0100, Maarten Lankhorst wrote:
> > > > > New update. Instead of calling it the 'dev' cgroup, it's now the
> > > > > 'dmem' cgroup.
> > > > > 
> > > > > Because it only deals with memory regions, the UAPI has been updated
> > > > > to use dmem.min/low/max/current, and to make the API cleaner, the
> > > > > names are changed too.
> > > > 
> > > > The API is much nicer, and fits much better into other frameworks too.
> > > > 
> > > > > dmem.current could contain a line like:
> > > > > "drm/0000:03:00.0/vram0 1073741824"
> > > > > 
> > > > > But I think using "drm/card0/vram0" instead of PCIID would perhaps be
> > > > > good too. I'm open to changing it to that based on feedback.
> > > > 
> > > > Do we have any sort of guarantee over the name card0 being stable across
> > > > reboots?
> > > > 
> > > > I also wonder if we should have a "total" device that limits the amount
> > > > of memory we can allocate from any region?
> > > 
> > > I don't think it is useful. Say your app can use 1 GB of main memory or 2 GB
> > > of VRAM, it wouldn't make sense to limit the total of those. In a lot of
> > > cases there is only 1 region, so the total of that would still be the same.
> > > 
> > > On top, we just separated the management of each region, adding a 'total'
> > > would require unseparating it again. :-)
> > 
> > I didn't mean the total for a device, but for the system. It would
> > definitely not make sense for a VRAM, but for CMA for example, you have
> > a single, limited, allocator that will be accessible from heaps, v4l2
> > and DRM devices.
> > 
> > If an application has to allocate both from v4l2 and DRM buffers, we
> > should be able to limit its total usage of CMA, not just on a single
> > device.
>
> In this case, I think it makes more sense if CMA creates a region, then use
> that region in both v4l2 and DRM instead of a separate region for both, with
> CMA being responsible for lifetime.

Ack, thanks for your feedback :)

Maxime

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