Re: [RFC v4 5/8] dmabuf: Add gpu cgroup charge transfer function

[T.J. Mercier]

On Tue, Apr 5, 2022 at 5:12 AM Michal Koutný <mkoutny@xxxxxxxx> wrote:
>
> On Fri, Apr 01, 2022 at 11:41:36AM -0700, "T.J. Mercier" <tjmercier@xxxxxxxxxx> wrote:
> > This link doesn't work for me, but I think you're referring to the
> > discussion about your "RAM_backed_buffers" comment from March 23rd.
>
> (Oops, it's a non-public message. But yes, you guessed it right ;-))
>
> > Anyway the test I did goes like this: enable memcg and gpu cgoups
> > tracking and run a process that allocates 100MiB of dmabufs. Observe
> > memcg and gpu accounting values before and after the allocation.
>
> Thanks for this measurement/dem/demoo.
>
> > Before
> > # cat memory.current gpu.memory.current
> > 14909440
> > system 0
> >
> > <Test program does the allocation of 100MiB of dmabufs>
> >
> > After
> > # cat memory.current gpu.memory.current
> > 48025600
> > system 104857600
> >
> > So the memcg value increases by about 30 MiB while the gpu values
> > increases by 100 MiB.
>
> > This is with kmem enabled, and the /proc/maps
> > file for this process indicates that the majority of that 30 MiB is
> > kernel memory.
>
> > I think this result shows that neither the kernel nor process memory
> > overlap with the gpu cgroup tracking of these allocations.
>
> It depends how the semantics of the 'system' entry is defined, no?
> As I grasped from other thread, the 'total' is going to be removed, so
> 'system' represents exclusively device memory?
>
That's right. The system charges (soon to be renamed "system-heap")
result only from an allocator (in this case the system heap) deciding
to call gpucg_try_charge for the buffer which is entirely device
memory.
>
> > So despite the fact that these buffers are in main memory, they are
> > allocated in a way that does not result in memcg attribution. (It
> > looks to me like __GFP_ACCOUNT is not set for these.)
>
> (I thought you knew what dmabufs your program used :-p)
>
I'm coming up to speed on a lot of new-to-me code here. :)
Just for completeness, these buffers were allocated with
libdmabufheap's AllocSystem.

> So, the goal is to do the tracking and migrations only via the gpu cg
> layer, regardless how memcg charges it (or not).
>
> (I have no opinion on that, I'm just summing it so that we're on the
> same page.)
>
Yes, this reflects my intention and current state of the code in this series.

> Michal

Thanks,
T.J.