On 2022/11/3 16:50, Ming Lei wrote: > Hello Guys, > > This patch extends io_uring/splice by adding two flags(SPLICE_F_DIRECT & > SPLICE_F_READ_TO_READ) for supporting ublk zero copy, and fuse could benefit > from the change too. > > - SPLICE_F_DIRECT is for using do_splice_direct() to support zero copy > > - SPLICE_F_READ_TO_READ is for supporting ublk READ zero copy, the plain > splice can support WRITE zero copy by: > > splice(ublkc_fd, ublkc_pos, pipe_wr_fd, NULL, len, flags) > splice(pipe_rd_fd, NULL, backing_fd, backing_off, len, flags) > > but can't support READ zc. Extend splice to allow to splice from the 1st > ->splice_read()(producer) to the 2nd ->splice_read()(consumer), then READ > request pages reference can be transferred to backing IO code path. > > The initial idea is suggested by Miklos Szeredi & Stefan Hajnoczi. > > The patchset has been verified basically by ublk builtin tests(loop/008, > loop/009, generic/003), and basic mount, git clone, kernel building, umount > tests on ublk-loop[1] which is created by 'ublk add -t loop -f $backing -z'. > > The next step is to allow io_uring to run do_splice_direct*() > in async style like normal async RW instead of offloading to > iowq context, so that top performance can be reached, and that > depends on current work. > > Any comments are welcome. > > [1] https://github.com/ming1/ubdsrv/commits/splice-zc > > > Ming Lei (4): > io_uring/splice: support do_splice_direct > fs/splice: add helper of splice_dismiss_pipe() > io_uring/splice: support splice from ->splice_read to ->splice_read > ublk_drv: support splice based read/write zero copy > > drivers/block/ublk_drv.c | 151 +++++++++++++++++++++++++- > fs/read_write.c | 5 +- > fs/splice.c | 193 +++++++++++++++++++++++++++++----- > include/linux/fs.h | 2 + > include/linux/pipe_fs_i.h | 9 ++ > include/linux/splice.h | 14 +++ > include/uapi/linux/ublk_cmd.h | 34 +++++- > io_uring/splice.c | 16 ++- > 8 files changed, 392 insertions(+), 32 deletions(-) > Hi, Ming I have quickly scanned the code. It seems like biovec pages are successfully passed to the backend for READ/WRITE. I will learn your code and run some tests. I will give more feedback next week. Regards, Zhang
