[Devel] [PATCH v5 0/8] per-cgroup tcp buffer pressure settings

[Glauber Costa]

[[ v3: merge Kirill's suggestions, + a destroy-related bugfix ]]
[[ v4: Fix a bug with non-mounted cgroups + disallow task movement ]]
[[ v5: Compile bug with modular ipv6 + tcp files in bytes ]]

Kame, Kirill,

I am submitting this again merging most of your comments. I've decided to
leave some of them out:
 * I am not using res_counters for allocated_memory. Besides being more
   expensive than what we need, to make it work in a nice way, we'd have
   to change the !cgroup code, including other protocols than tcp. Also,
   
 * I am not using failcnt and max_usage_in_bytes for it. I believe the value
   of those lies more in the allocation than in the pressure control. Besides,
   fail conditions lie mostly outside of the memory cgroup's control. (Actually,
   a soft_limit makes a lot of sense, and I do plan to introduce it in a follow
   up series)

If you agree with the above, and there are any other pressing issues, let me
know and I will address them ASAP. Otherwise, let's discuss it. I'm always open.

All:

This patch introduces per-cgroup tcp buffers limitation. This allows
sysadmins to specify a maximum amount of kernel memory that
tcp connections can use at any point in time. TCP is the main interest
in this work, but extending it to other protocols would be easy.

For this to work, I am hooking it into memcg, after the introdution of
an extension for tracking and controlling objects in kernel memory.
Since they are usually not found in page granularity, and are fundamentally
different from userspace memory (not swappable, can't overcommit), they
need their special place inside the Memory Controller.

Right now, the kmem extension is quite basic, and just lays down the
basic infrastucture for the ongoing work.

Although it does not account kernel memory allocated - I preferred to
keep this series simple and leave accounting to the slab allocations when
they arrive.

What it does is to piggyback in the memory control mechanism already present in
/proc/sys/net/ipv4/tcp_mem. There is a soft limit, and a hard limit,
that will suppress allocation when reached. For each non-root cgroup, however,
the file kmem.tcp_maxmem will be used to cap those values.

The usage I have in mind here is containers. Each container will
define its own values for soft and hard limits, but none of them will
be possibly bigger than the value the box' sysadmin specified from
the outside.

To test for any performance impacts of this patch, I used netperf's
TCP_RR benchmark on localhost, so we can have both recv and snd in action.
For this iteration, I am using the 1% confidence interval as suggested by Rick.

Command line used was ./src/netperf -t TCP_RR -H localhost -i 30,3 -I 99,1 and the
results: (I haven't re-run this since nothing major changed from last version, nothing
in core)

Without the patch
=================

Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384  87380  1        1       10.00    35356.22
16384  87380


With the patch
==============

Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384  87380  1        1       10.00    35399.12 
16384  87380

The difference is less than 0.5 %

A simple test with a 1000 level nesting yields more or less the same
difference:

1000 level nesting
==================

Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384  87380  1        1       10.00    35304.35   
16384  87380 



Glauber Costa (8):
  Basic kernel memory functionality for the Memory Controller
  socket: initial cgroup code.
  foundations of per-cgroup memory pressure controlling.
  per-cgroup tcp buffers control
  per-netns ipv4 sysctl_tcp_mem
  tcp buffer limitation: per-cgroup limit
  Display current tcp memory allocation in kmem cgroup
  Disable task moving when using kernel memory accounting

 Documentation/cgroups/memory.txt |   38 ++++-
 crypto/af_alg.c                  |    7 +-
 include/linux/memcontrol.h       |   56 ++++++
 include/net/netns/ipv4.h         |    1 +
 include/net/sock.h               |  127 +++++++++++++-
 include/net/tcp.h                |   29 +++-
 include/net/udp.h                |    3 +-
 include/trace/events/sock.h      |   10 +-
 init/Kconfig                     |   14 ++
 mm/memcontrol.c                  |  371 ++++++++++++++++++++++++++++++++++++--
 net/core/sock.c                  |  104 ++++++++---
 net/decnet/af_decnet.c           |   21 ++-
 net/ipv4/proc.c                  |    7 +-
 net/ipv4/sysctl_net_ipv4.c       |   71 +++++++-
 net/ipv4/tcp.c                   |   58 ++++---
 net/ipv4/tcp_input.c             |   12 +-
 net/ipv4/tcp_ipv4.c              |   24 ++-
 net/ipv4/tcp_output.c            |    2 +-
 net/ipv4/tcp_timer.c             |    2 +-
 net/ipv4/udp.c                   |   20 ++-
 net/ipv6/tcp_ipv6.c              |   20 ++-
 net/ipv6/udp.c                   |    4 +-
 net/sctp/socket.c                |   35 +++-
 23 files changed, 905 insertions(+), 131 deletions(-)

-- 
1.7.6