[PATCHSET RFC 0/7] Add support for provided registered buffers

[Jens Axboe <axboe@kernel.dk>]

Hi,

Normally a request can take a provided buffer, which means "pick a
buffer from group X and do IO to/from it", or it can use a registered
buffer, which means "use the buffer at index Y and do IO to/from it".
For things like O_DIRECT and network zero copy, registered buffers can
be used to speedup the operation, as they avoid repeated
get_user_pages() and page referencing calls for each IO operation.

Normal (non zero copy) send supports bundles, which is a way to pick
multiple provided buffers at once and send them. send zero copy only
supports registered buffers, and hence can only send a single buffer
at the time.

This patchset adds support for using a mix of provided and registered
buffers, where the provided buffers merely provide an index into which
registered buffers to use. This enables using provided buffers for
send zc in general, but also bundles where multiple buffers are picked.
This is done by changing how the provided buffers are intepreted.
Normally a provided buffer has an address, length, and buffer ID
associated with it. The address tells the kernel where the IO should
occur. If both fixed and provided buffers are asked for, the provided
buffer address field is instead an encoding of the registered buffer
index and the offset within that buffer. With that in place, using a
combination of the two can work.

Patches 1-4 are just cleanup and prep, patch 5 adds the basic
definition of what a fixed provided buffer looks like, patch 6 adds
support for kbuf to map into a bvec directly, and finally patch 7
adds support for send zero copy to use this mechanism.

More details available in the actual patches. Tested with kperf using
zero copy RX and TX, easily reaching 100G speeds with a single thread
doing 4k sends and receives.

Kernel tree here:

https://git.kernel.dk/cgit/linux/log/?h=io_uring-sendzc-provided

 include/uapi/linux/io_uring.h |   8 ++
 io_uring/kbuf.c               | 180 +++++++++++++++++++++++++++----
 io_uring/kbuf.h               |   9 +-
 io_uring/net.c                | 192 ++++++++++++++++++++++------------
 io_uring/net.h                |  10 +-
 io_uring/opdef.c              |   1 +
 6 files changed, 309 insertions(+), 91 deletions(-)

-- 
Jens Axboe