[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@xxxxxxxxxx> > --- > 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,
