Re: [PATCH v2 0/3] dma-buf: heaps: cma: enable dmem cgroup accounting

[Maxime Ripard]

Hi Christian,

On Fri, Feb 20, 2026 at 10:45:08AM +0100, Christian König wrote:
> On 2/20/26 02:14, T.J. Mercier wrote:
> > On Wed, Feb 18, 2026 at 9:15 AM Eric Chanudet <echanude@xxxxxxxxxx> wrote:
> > 
> > Hi Eric,
> > 
> >> An earlier series[1] from Maxime introduced dmem to the cma allocator in
> >> an attempt to use it generally for dma-buf. Restart from there and apply
> >> the charge in the narrower context of the CMA dma-buf heap instead.
> >>
> >> In line with introducing cgroup to the system heap[2], this behavior is
> >> enabled based on dma_heap.mem_accounting, disabled by default.
> >>
> >> dmem is chosen for CMA heaps as it allows limits to be set for each
> >> region backing each heap. The charge is only put in the dma-buf heap for
> >> now as it guaranties it can be accounted against a userspace process
> >> that requested the allocation.
> > 
> > But CMA memory is system memory, and regular (non-CMA) movable
> > allocations can occur out of these CMA areas. So this splits system
> > memory accounting between memcg (from [2]) and dmem. If I want to put
> > a limit on system memory use I have to adjust multiple limits (memcg +
> > dmems) and know how to divide the total between them all.
> > 
> > How do you envision using this combination of different controllers?
> 
> Yeah we have this problem pretty much everywhere.
> 
> There are both use cases where you want to account device allocations
> to memcg and when you don't want that.
> 
> From what I know at the moment it would be best if the administrator
> could say for each dmem if it should account additionally to memcg or
> not.
> 
> Using module parameters to enable/disable it globally is just a
> workaround as far as I can see.

That's a pretty good idea! It would indeed be a solution that could
satisfy everyone (I assume?).

Maxime

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