[PATCHSET,v2,RFC,0/13] Rewrite rsrc node handling

Message

Jens Axboe Oct. 28, 2024, 2:52 p.m. UTC

Hi,

v2 of this RFC, now a bit more polished and split up.

For a full explanation of the goal of the series, see patch #6 and #10.
tldr is that our currently rsrc node handling can block freeing of
resources for an indeterminite amount of time, which is very unfortunate
for potentially long lived request. For example, networked workloads and
using fixed files, where a previously long lived socket has the full
resource tables of the entire ring pinned. That can lead to files being
held open for a very long time, where they should be freed+closed
instead.

This series handles the resource nodes separately, so a request pins
just the resources it needs, and only for the duration of that request.
In doing so, it also unifies how these resources are tracked. As it
stands, the current kernel duplicates state across user_bufs and
buf_data, and ditto for the file_table and file_data. Not only is some
of it duplicated (like the node arrays), it also needs to alloc and
copy the tags that are potentially associated with the resource. With
the unification, state is only in one spot for each type of resource,
and tags are handled at registration time rather than needing to be
retained for the duration of the resource. As with cleaning up of
structures, it also shrinks io_ring_ctx by 64b (should be more, it
adds holes too in spots), and the actual resource node goes from
needing 48b and 16b of put info, to 32b.

Tests out well here, both liburing test suite but also application
testing. Most notably, the infamous test case that held all 10k
sockets open during new opens and updates now only has the few open
you'd expect. And it removes a net of about 280 lines of core io_uring
code. In my opinion, it's also easier to follow.

Can also be found here:

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

Changes since v1:
- Rebase on -rc5 + pending io_uring work. Each step now works, as it
  should, and passes testing.
- Add and use node lookup helper consistently
- Add a few patches killing mostly useless helpers
- Split out patches from the main bigger patches
- Fix an assumption in test/rsrc_tags.c that prevented it from working
  with the per-node refs
- Add NOP patch that enables testing of both registered files and
  buffers
- Remove 'index' struct io_rsrc_node, it was unused now. That shrinks
  the node size fo 32b, fitting two in a cacheline.

 include/linux/io_uring_types.h |  25 +-
 include/uapi/linux/io_uring.h  |   3 +
 io_uring/cancel.c              |   8 +-
 io_uring/fdinfo.c              |  14 +-
 io_uring/filetable.c           |  79 ++---
 io_uring/filetable.h           |  37 +--
 io_uring/io_uring.c            |  51 +--
 io_uring/msg_ring.c            |  33 +-
 io_uring/net.c                 |  16 +-
 io_uring/nop.c                 |  47 ++-
 io_uring/notif.c               |   3 +-
 io_uring/opdef.c               |   2 +
 io_uring/register.c            |   3 +-
 io_uring/rsrc.c                | 587 +++++++++++----------------------
 io_uring/rsrc.h                |  96 +++---
 io_uring/rw.c                  |  15 +-
 io_uring/splice.c              |  42 ++-
 io_uring/splice.h              |   1 +
 io_uring/uring_cmd.c           |  20 +-
 19 files changed, 437 insertions(+), 645 deletions(-)