[PATCH 00/11] sysv ipc shared mem optimizations

[Davidlohr Bueso]

This is the third and final patchset that deals with reducing the
amount of contention we impose on the ipc lock (kern_ipc_perm.lock).
These changes mostly deal with shared memory, previous work has already
been done for semaphores and message queues:

http://lkml.org/lkml/2013/3/20/546 (sems)
http://lkml.org/lkml/2013/5/15/584 (mqueues)

With these patches applied, a custom shm microbenchmark stressing shmctl
doing IPC_STAT with 4 threads a million times, reduces the execution time by 50%.
A similar run, this time with IPC_SET, reduces the execution time from 3 mins and
35 secs to 27 seconds.

Patches 1-8: replaces blindly taking the ipc lock for a smarter combination
of rcu and ipc_obtain_object, only acquiring the spinlock when updating.

Patch 9: renames the ids rw_mutex to rwsem, which is what it already was.

Patch 10: is a trivial mqueue leftover cleanup

Patch 11: adds a brief lock scheme description, requested by Andrew.

This patchset applies on top of linux-next (3.10.0-rc6-next-20130618).

Davidlohr Bueso (11):
  ipc,shm: introduce lockless functions to obtain the ipc object
  ipc,shm: shorten critical region in shmctl_down
  ipc: drop ipcctl_pre_down
  ipc,shm: introduce shmctl_nolock
  ipc,shm: make shmctl_nolock lockless
  ipc,shm: shorten critical region for shmctl
  ipc,shm: cleanup do_shmat pasta
  ipc,shm: shorten critical region for shmat
  ipc: rename ids->rw_mutex
  ipc,msg: drop msg_unlock
  ipc: document general ipc locking scheme

 include/linux/ipc_namespace.h |   2 +-
 ipc/msg.c                     |  25 +++--
 ipc/namespace.c               |   4 +-
 ipc/sem.c                     |  24 ++---
 ipc/shm.c                     | 239 ++++++++++++++++++++++++++----------------
 ipc/util.c                    |  57 +++++-----
 ipc/util.h                    |   7 +-
 7 files changed, 199 insertions(+), 159 deletions(-)

-- 
1.7.11.7

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