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

[Maarten Lankhorst <dev@lankhorst.se>]

Hey,

Now that all patches look good, what is needed to merge the series? 
Without patch 6/7 as it is a hack for testing.

I've also posted a IGT for verifying read/write works (rule out 
copy/paste errors) and min, max semantics work as intended.

https://lists.freedesktop.org/archives/igt-dev/2024-December/083345.html

Cheers,
~Maarten


Den 2024-12-17 kl. 08:46, skrev Maxime Ripard:
> 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,l
>>>>>
>>>>> 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