[PATCH v2 0/8] sunrpc: Reduce lock contention for NFSD TCP sockets

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

High-throughput NFSD workloads exhibit significant lock contention on
TCP connections. Worker threads compete for the socket lock during
receives and serialize on xpt_mutex during sends, limiting scalability.

This series addresses both paths:

 - Receive: A dedicated kernel thread per TCP connection owns all
   sock_recvmsg() calls and queues complete RPC messages for workers
   via lock-free llist. This eliminates socket lock contention among
   workers.

 - Transmit: Flat combining allows one thread to send on behalf of
   multiple waiters. Threads enqueue requests; the mutex holder
   ("combiner") processes the batch, amortizing lock acquisition and
   enabling TCP segment coalescing via MSG_MORE.

Supporting changes include a page recycling pool for receive buffers,
and explicit TCP buffer sizing for high bandwidth-delay product
networks.

Base commit: v6.19
URL: https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/log/?h=svctcp-next

---

Changes since RFC:
- Drop the affinity scope patch
- Skip user memory hardening for kernel-to-kernel copies
- Avoid invoking wake_up when the receive is already running
- Refactor svc_tcp_receiver_thread() for legibility
- Do not set MSG_MORE during batched sends

Chuck Lever (8):
  sunrpc: Add XPT flags missing from SVC_XPRT_FLAG_LIST
  net: datagram: bypass usercopy checks for kernel iterators
  sunrpc: split svc_data_ready into protocol-specific callbacks
  sunrpc: add per-transport page recycling pool
  sunrpc: add dedicated TCP receiver thread
  sunrpc: implement flat combining for TCP socket sends
  sunrpc: unify fore and backchannel server TCP send paths
  sunrpc: Set explicit TCP socket buffer sizes for NFSD

 include/linux/sunrpc/svc.h      |   1 +
 include/linux/sunrpc/svc_xprt.h |  32 ++
 include/linux/sunrpc/svcsock.h  |  40 ++
 include/trace/events/sunrpc.h   |   7 +-
 net/core/datagram.c             |  15 +-
 net/sunrpc/svc.c                |  13 +
 net/sunrpc/svc_xprt.c           | 151 ++++++
 net/sunrpc/svcsock.c            | 802 +++++++++++++++++++++++++++++---
 net/sunrpc/xprtsock.c           |  60 +--
 9 files changed, 999 insertions(+), 122 deletions(-)

-- 
2.52.0