On Thu, Jan 18, 2024 at 11:02:22AM +0100, Christian König wrote: > Am 17.01.24 um 19:11 schrieb T.J. Mercier: > > DMA buffers allocated from the CMA dma-buf heap get counted under > > RssFile for processes that map them and trigger page faults. In > > addition to the incorrect accounting reported to userspace, reclaim > > behavior was influenced by the MM_FILEPAGES counter until linux 6.8, but > > this memory is not reclaimable. [1] Change the CMA dma-buf heap to set > > VM_PFNMAP on the VMA so MM does not poke at the memory managed by this > > dma-buf heap, and use vmf_insert_pfn to correct the RSS accounting. > > > > The system dma-buf heap does not suffer from this issue since > > remap_pfn_range is used during the mmap of the buffer, which also sets > > VM_PFNMAP on the VMA. > > Mhm, not an issue with this patch but Daniel wanted to add a check for > VM_PFNMAP to dma_buf_mmap() which would have noted this earlier. > > I don't fully remember the discussion but for some reason that was never > committed. We should probably try that again. Iirc the issue is that dma_mmap is not guaranteed to give you a VM_SPECIAL mapping, at least on absolutely all architectures. That's why I defacto dropped that idea, but it would indeed be really great if we could resurrect it. Maybe for x86 only? Or x86+armv8, I'm honestly not sure anymore which exact cases ended up with a VM_NORMAL mapping ... Would need a pile of digging. I think all the other patches I've landed. -Sima > > > [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/mm/vmscan.c?id=fb46e22a9e3863e08aef8815df9f17d0f4b9aede > > > > Fixes: b61614ec318a ("dma-buf: heaps: Add CMA heap to dmabuf heaps") > > Signed-off-by: T.J. Mercier<tjmercier@xxxxxxxxxx> > > Acked-by: Christian König <christian.koenig@xxxxxxx> > > > --- > > drivers/dma-buf/heaps/cma_heap.c | 7 +++---- > > 1 file changed, 3 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c > > index ee899f8e6721..4a63567e93ba 100644 > > --- a/drivers/dma-buf/heaps/cma_heap.c > > +++ b/drivers/dma-buf/heaps/cma_heap.c > > @@ -168,10 +168,7 @@ static vm_fault_t cma_heap_vm_fault(struct vm_fault *vmf) > > if (vmf->pgoff > buffer->pagecount) > > return VM_FAULT_SIGBUS; > > - vmf->page = buffer->pages[vmf->pgoff]; > > - get_page(vmf->page); > > - > > - return 0; > > + return vmf_insert_pfn(vma, vmf->address, page_to_pfn(buffer->pages[vmf->pgoff])); > > } > > static const struct vm_operations_struct dma_heap_vm_ops = { > > @@ -185,6 +182,8 @@ static int cma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma) > > if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0) > > return -EINVAL; > > + vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); > > + > > vma->vm_ops = &dma_heap_vm_ops; > > vma->vm_private_data = buffer; -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
