Hi David, I would love to participate in this discussion and the page migration/tmp-page discussions, but I don't think I can make to to LSF/MM. On 1/30/25 22:28, David Wei wrote: > Hi folks, I want to propose a discussion on adding zero copy to FUSE > io_uring in the kernel. The source is some userspace buffer or device > memory e.g. GPU VRAM. The destination is FUSE server in userspace, which > will then either forward it over the network or to an underlying > FS/block device. The FUSE server may want to read the data. > > My goal is to eliminate copies in this entire data path, including the > initial hop between the userspace client and the kernel. I know Ming and > Keith are working on adding ublk zero copy but it does not cover this > initial hop and it does not allow the ublk/FUSE server to read the data. > > My idea is to use shared memory or dma-buf, i.e. the source data is > encapsulated in an mmap()able fd. The client and FUSE server exchange > this fd through a back channel with no kernel involvement. The FUSE > server maps the fd into its address space and registers the fd with > io_uring via the io_uring_register() infra. When the client does e.g. a > DIO write, the pages are pinned and forwarded to FUSE kernel, which does > a lookup and understands that the pages belong to the fd that was > registered from the FUSE server. Then io_uring tells the FUSE server > that the data is in the fd it registered, so there is no need to copy > anything at all. For specific applications that know the protocol that should. > > I would like to discuss this and get feedback from the community. My top > question is why do this in the kernel at all? It is entirely possible to > bypass the kernel entirely by having the client and FUSE server exchange > the fd and then do the I/O purely through IPC. Because we leave posix and it is rather fuse specific then. Thanks, Bernd
