[PATCH v1 net-next 0/8] tcp: Prevent tcp_collapse() from bloating queue.

[Kuniyuki Iwashima <kuniyu@google.com>]

This is a follow-up for commit 031c403d13e5 ("tcp: do not let
tcp_collapse() drive sk_forward_alloc negative").

The core algorithm in tcp_collapse() is so simple and has not
been changed since commit 1da177e4c3f4 ("Linux-2.6.12-rc2");
finding a collapsible skb and repacking it into up-to-SKB_MAX_ORDER()
skb.

Now that we use 4K MSS and tp->scaling_ratio, the simple algorithm
does not work well, and it could even end up consuming more memory
contrary to the intention.

For example, the scaling ratio of SKB_MAX_ORDER() is 222, but
typically tp->scaling_ratio for 4K MSS flow is 252, and repacking
data rather bloats high-density skb.

Also, once a low-density skb starts collapsing, it drags all the
following skbs into collapsing regardless of the density.

This series changes the algorithm so that it skips high-density
skb and a single low-density skb between high-density skbs, batches
memory accounting at the end, and removes sk_forced_mem_schedule().


Kuniyuki Iwashima (8):
  tcp: Clean up the first loop in tcp_collapse().
  tcp: Don't collapse high density skb.
  tcp: Stop collapsing if not bloated.
  net: Move SKB_SMALL_HEAD_CACHE_SIZE to skbuff.h.
  tcp: Skip collapsing if collapsed skb is less-dense.
  tcp: Allocate all new skb before collapsing.
  tcp: Batch memory accounting in tcp_collapse().
  selftest: packetdrill: Add test for tcp_collapse().

 include/linux/skbuff.h                        |  25 +++
 include/net/gro.h                             |   3 -
 include/net/tcp.h                             |   1 -
 net/core/skbuff.c                             |  13 --
 net/ipv4/tcp_input.c                          | 171 +++++++++++++-----
 .../selftests/net/packetdrill/ksft_runner.sh  |   9 +
 .../net/packetdrill/tcp_collapse.pkt          | 135 ++++++++++++++
 7 files changed, 292 insertions(+), 65 deletions(-)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_collapse.pkt

-- 
2.56.0.611.g1030f0b940-goog