[PATCH RFC 00/12] dma: Enable dmem cgroup tracking

Maxime Ripard
2025-03-10T12:06:19Z

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,
--
Maxime Ripard <mripard@kernel.org>