[PATCH net-next 0/7] net: reduce tcp_memory_allocated inflation

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

Hosts with a lot of sockets tend to hit so called TCP memory pressure,
leading to very bad TCP performance and/or OOM.

The problem is that some TCP sockets can hold up to 2MB of 'forward
allocations' in their per-socket cache (sk->sk_forward_alloc),
and there is no mechanism to make them relinquish their share
under mem pressure.
Only under some potentially rare events their share is reclaimed,
one socket at a time.

In this series, I implemented a per-cpu cache instead of a per-socket one.

Each CPU has a +1/-1 MB (256 pages on x86) forward alloc cache, in order
to not dirty tcp_memory_allocated shared cache line too often.

We keep sk->sk_forward_alloc values as small as possible, to meet
memcg page granularity constraint.

Note that memcg already has a per-cpu cache, although MEMCG_CHARGE_BATCH
is defined to 32 pages, which seems a bit small.

Note that while this cover letter mentions TCP, this work is generic
and supports TCP, UDP, DECNET, SCTP.

Eric Dumazet (7):
  Revert "net: set SK_MEM_QUANTUM to 4096"
  net: remove SK_MEM_QUANTUM and SK_MEM_QUANTUM_SHIFT
  net: add per_cpu_fw_alloc field to struct proto
  net: implement per-cpu reserves for memory_allocated
  net: fix sk_wmem_schedule() and sk_rmem_schedule() errors
  net: keep sk->sk_forward_alloc as small as possible
  net: unexport __sk_mem_{raise|reduce}_allocated

 include/net/sock.h           | 100 +++++++++++++++--------------------
 include/net/tcp.h            |   2 +
 include/net/udp.h            |   1 +
 net/core/datagram.c          |   3 --
 net/core/sock.c              |  22 ++++----
 net/decnet/af_decnet.c       |   4 ++
 net/ipv4/tcp.c               |  13 ++---
 net/ipv4/tcp_input.c         |   6 +--
 net/ipv4/tcp_ipv4.c          |   3 ++
 net/ipv4/tcp_output.c        |   2 +-
 net/ipv4/tcp_timer.c         |  19 ++-----
 net/ipv4/udp.c               |  14 +++--
 net/ipv4/udplite.c           |   3 ++
 net/ipv6/tcp_ipv6.c          |   3 ++
 net/ipv6/udp.c               |   3 ++
 net/ipv6/udplite.c           |   3 ++
 net/iucv/af_iucv.c           |   2 -
 net/mptcp/protocol.c         |  13 +++--
 net/sctp/protocol.c          |   4 +-
 net/sctp/sm_statefuns.c      |   2 -
 net/sctp/socket.c            |  12 +++--
 net/sctp/stream_interleave.c |   2 -
 net/sctp/ulpqueue.c          |   4 --
 23 files changed, 114 insertions(+), 126 deletions(-)

-- 
2.36.1.255.ge46751e96f-goog