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

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Message-ID: <5a50a992-9286-4179-8031-ffb514bca34f@lankhorst.se>
Date: Fri, 13 Dec 2024 17:06:05 +0100
From: Maarten Lankhorst <dev@...khorst.se>
To: Maxime Ripard <mripard@...nel.org>
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.

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.

Cheers,
~Maarten