[PATCH v6 mptcp-next 0/7] mptcp: address stall under memory pressure

[Paolo Abeni <pabeni@redhat.com>]

This an attempt to fix the data transfer stall reported by Geliang and
Gang more carefully enforcing memory constraints at the MPTCP level.

This iteration presents a significant change WRT the previous one,
avoiding entirely the collapse attempt on memory pressure. Note that
this choice represent a trade off: collapsing allow much faster transfer
(to be more accurate: order of magnitude less slow) under some extreme
conditions, but makes transfer slower and much more CPU intensive for
less unlikely conditions.

As a consequence of the above the `mptcp_data.multi_chunk_sendfile`
test-case needs a 240 seconds timeout to complete successfully:

TEST_F_TIMEOUT(mptcp, multi_chunk_sendfile, 240)

The solution performing data collapsing would need similar long timeout
for the multiproc tests cases: mutliproc_even, mutliproc_readers,
mutliproc_writers, mutliproc_sendpage_even, mutliproc_sendpage_readers,
mutliproc_sendpage_writers.

Patch 1 is new in v6, and is actually a fix for an old issue (targeting
net), included here just for my convenience.

Patch 2 and 3 makes the admission check much more strict for incoming
packets exceeding the memory limits, with some exception for fallback
sockets.
Patch 4 makes implement OoO queue pruning for MPTCP and patch 5
addresses an edge scenario that could still lead to transfer stall
under memory pressure.
Finally patch 6 and 7 improve the MPTCP-level retransmission schema to
make recovery from memory pressure/after MPTCP-level drop significanly
faster.
---
Paolo Abeni (7):
  mptcp: fix missing wakeups in edge scenarios
  mptcp: explicitly drop over memory limits
  mptcp: enforce hard limit on backlog flushing
  mptcp: implemented OoO queue pruning
  mptcp: track prune recovery status
  mptcp: move the retrans loop to a separate helper
  mptcp: let the retrans scheduler do its job.

 net/mptcp/mib.c      |   2 +
 net/mptcp/mib.h      |   2 +
 net/mptcp/options.c  |  67 +++++++++++-
 net/mptcp/protocol.c | 249 ++++++++++++++++++++++++++++++++-----------
 net/mptcp/protocol.h |   4 +
 net/mptcp/subflow.c  |   1 +
 6 files changed, 259 insertions(+), 66 deletions(-)

-- 
2.54.0