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

["T.J. Mercier" <tjmercier@google.com>]

On Wed, Feb 18, 2026 at 9:15 AM Eric Chanudet <echanude@redhat.com> 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?

Thanks,
T.J.

> [1] https://lore.kernel.org/all/20250310-dmem-cgroups-v1-0-2984c1bc9312@kernel.org/
> [2] https://lore.kernel.org/all/20260116-dmabuf-heap-system-memcg-v3-0-ecc6b62cc446@redhat.com/
>
> Signed-off-by: Eric Chanudet <echanude@redhat.com>
> ---
> Changes in v2:
> - Rebase on Maxime's introduction of dmem to the cma allocator:
>   https://lore.kernel.org/all/20250310-dmem-cgroups-v1-0-2984c1bc9312@kernel.org/
> - Remove the dmem region registration from the cma dma-buf heap
> - Remove the misplaced logic for the default region.
> - Link to v1: https://lore.kernel.org/r/20260130-dmabuf-heap-cma-dmem-v1-1-3647ea993e99@redhat.com
>
> ---
> Eric Chanudet (1):
>       dma-buf: heaps: cma: charge each cma heap's dmem
>
> Maxime Ripard (2):
>       cma: Register dmem region for each cma region
>       cma: Provide accessor to cma dmem region
>
>  drivers/dma-buf/heaps/cma_heap.c | 15 ++++++++++++++-
>  include/linux/cma.h              |  9 +++++++++
>  mm/cma.c                         | 20 +++++++++++++++++++-
>  mm/cma.h                         |  3 +++
>  4 files changed, 45 insertions(+), 2 deletions(-)
> ---
> base-commit: 948e195dfaa56e48eabda591f97630502ff7e27e
> change-id: 20260128-dmabuf-heap-cma-dmem-f4120a2df4a8
>
> Best regards,
> --
> Eric Chanudet <echanude@redhat.com>
>