[PATCH net-next 0/5] tcp: better visibility when receive queues are full

[Eric Dumazet <edumazet@kernel.org>]

When a TCP socket can not queue an incoming packet, it is currently
hard to tell why, and how often the stack had to work to make room.

Patch 1 adds TcpExtTCPRcvCollapseSkipped, counting the collapses
skipped by the rate limit added in commit c2213d9b61c1 ("tcp: rate
limit receive queue collapsing"). Patch 2 is the packetdrill test
for this rate limit.

Patch 3 reports SKB_DROP_REASON_SOCKET_RCVBUFF instead of
SKB_DROP_REASON_PROTO_MEM when the socket is over sk_rcvbuf.

Patch 4 adds SKB_DROP_REASON_MEMCG, to tell memory cgroup charge
failures from protocol memory limits.

Patch 5 adds a packetdrill test exercising tcp_collapse() on both
the out-of-order queue and the receive queue: no existing test
was reaching its copy loop.

Eric Dumazet (5):
  tcp: add TCPRcvCollapseSkipped counter
  selftests/net: packetdrill: add tcp_rcv_collapse_ratelimit.pkt
  tcp: use SKB_DROP_REASON_SOCKET_RCVBUFF when over sk_rcvbuf
  net: add SKB_DROP_REASON_MEMCG
  selftests/net: packetdrill: add tcp_rcv_collapse.pkt

 Documentation/networking/snmp_counter.rst     |   7 +
 include/net/dropreason-core.h                 |   6 +
 include/net/sock.h                            |  33 ++-
 include/uapi/linux/snmp.h                     |   1 +
 net/core/sock.c                               |  62 +++--
 net/ipv4/proc.c                               |   1 +
 net/ipv4/tcp_input.c                          |  42 ++--
 .../net/packetdrill/tcp_rcv_collapse.pkt      | 230 ++++++++++++++++++
 .../tcp_rcv_collapse_ratelimit.pkt            |  96 ++++++++
 9 files changed, 439 insertions(+), 39 deletions(-)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_collapse.pkt
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcv_collapse_ratelimit.pkt

-- 
2.53.0