[Adding Ben since we are currently in the middle of a discussion regarding exactly that problem]
Just for my understanding before I deep dive into the code: This uses a separate dmem cgroup and does not account against memcg, don't it?
Thanks, Christian.
Am 10.03.25 um 13:06 schrieb Maxime Ripard:
Hi,
Here's preliminary work to enable dmem tracking for heavy users of DMA allocations on behalf of userspace: v4l2, DRM, and dma-buf heaps.
It's not really meant for inclusion at the moment, because I really don't like it that much, and would like to discuss solutions on how to make it nicer.
In particular, the dma dmem region accessors don't feel that great to me. It duplicates the logic to select the proper accessor in dma_alloc_attrs(), and it looks fragile and potentially buggy to me.
One solution I tried is to do the accounting in dma_alloc_attrs() directly, depending on a flag being set, similar to what __GFP_ACCOUNT is doing.
It didn't work because dmem initialises a state pointer when charging an allocation to a region, and expects that state pointer to be passed back when uncharging. Since dma_alloc_attrs() returns a void pointer to the allocated buffer, we need to put that state into a higher-level structure, such as drm_gem_object, or dma_buf.
Since we can't share the region selection logic, we need to get the region through some other mean. Another thing I consider was to return the region as part of the allocated buffer (through struct page or folio), but those are lost across the calls and dma_alloc_attrs() will only get a void pointer. So that's not doable without some heavy rework, if it's a good idea at all.
So yeah, I went for the dumbest possible solution with the accessors, hoping you could suggest a much smarter idea :)
Thanks, Maxime
Signed-off-by: Maxime Ripard mripard@kernel.org
Maxime Ripard (12): cma: Register dmem region for each cma region cma: Provide accessor to cma dmem region dma: coherent: Register dmem region for each coherent region dma: coherent: Provide accessor to dmem region dma: contiguous: Provide accessor to dmem region dma: direct: Provide accessor to dmem region dma: Create default dmem region for DMA allocations dma: Provide accessor to dmem region dma-buf: Clear cgroup accounting on release dma-buf: cma: Account for allocations in dmem cgroup drm/gem: Add cgroup memory accounting media: videobuf2: Track buffer allocations through the dmem cgroup
drivers/dma-buf/dma-buf.c | 7 ++++ drivers/dma-buf/heaps/cma_heap.c | 18 ++++++++-- drivers/gpu/drm/drm_gem.c | 5 +++ drivers/gpu/drm/drm_gem_dma_helper.c | 6 ++++ .../media/common/videobuf2/videobuf2-dma-contig.c | 19 +++++++++++ include/drm/drm_device.h | 1 + include/drm/drm_gem.h | 2 ++ include/linux/cma.h | 9 +++++ include/linux/dma-buf.h | 5 +++ include/linux/dma-direct.h | 2 ++ include/linux/dma-map-ops.h | 32 ++++++++++++++++++ include/linux/dma-mapping.h | 11 ++++++ kernel/dma/coherent.c | 26 +++++++++++++++ kernel/dma/direct.c | 8 +++++ kernel/dma/mapping.c | 39 ++++++++++++++++++++++ mm/cma.c | 21 +++++++++++- mm/cma.h | 3 ++ 17 files changed, 211 insertions(+), 3 deletions(-)
base-commit: 55a2aa61ba59c138bd956afe0376ec412a7004cf change-id: 20250307-dmem-cgroups-73febced0989
Best regards,