On Fri, Jul 09, 2021 at 07:24:48PM +0900, Shunsuke Mie wrote: > Hi all, > > I tried to use Continuous Memory Allocator (CMA) allocated memory for > RDMA transfer buffer in userspace, but it failed. Sorry for my question, but why do you need it? >From that I remember, CMA memory is used for the devices that doesn't support scatter-gather, while RDMA devices (umem) need SG. Thanks > > For more details, an ibv_reg_mr() API fails when I pass an mmaped > memory region of allocated memory by the CMA. The reason why, a CMA > mmap function, __dma_mmap_from_coherent(), sets VM_IO and VM_PFNMAP > to vma->vm_flags, and an ib_uverbs_reg_mr(), kernel function > corresponding to the ibv_reg_mr(), tries to pin the memory region but, > it becomes to fail. because VM_IO or VM_PFNMAP regions cannot be > pined. As a result, the ibv_reg_mr() returns an error. > > I think the ib_umem_get() that is called in the ib_uverbs_reg_mr() and > pins memories needs some modifications to support RDMA transfer > to/from the CMA memory. > > I’d like to know your comments, ideas, and other solution. > > Thanks a lot, > Shunsuke.
