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.o... [2] https://lore.kernel.org/all/20260116-dmabuf-heap-system-memcg-v3-0-ecc6b62cc...
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.o...
- 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@re...
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