aio: add aio_kernel_() interface

This adds an interface that lets kernel callers submit aio iocbs without
going through the user space syscalls.  This lets kernel callers avoid
the management limits and overhead of the context.  It will also let us
integrate aio operations with other kernel apis that the user space
interface doesn't have access to.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
aio: add aio support for iov_iter arguments

This adds iocb cmds which specify that memory is held in iov_iter
structures.  This lets kernel callers specify memory that can be
expressed in an iov_iter, which includes pages in bio_vec arrays.

Only kernel callers can provide an iov_iter so it doesn't make a lot of
sense to expose the IOCB_CMD values for this as part of the user space
ABI.

But kernel callers should also be able to perform the usual aio
operations which suggests using the the existing operation namespace and
support code.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: Zach Brown <zab@zabbo.net>
modified for Mako from LKML reference

Signed-off-by: faux123 <reioux@gmail.com>
aio: convert the ioctx list to radix tree

Date	Wed, 3 Apr 2013 16:20:48 +0300

When using a large number of threads performing AIO operations the
IOCTX list may get a significant number of entries which will cause
significant overhead. For example, when running this fio script:

rw=randrw; size=256k ;directory=/mnt/fio; ioengine=libaio; iodepth=1
blocksize=1024; numjobs=512; thread; loops=100

on an EXT2 filesystem mounted on top of a ramdisk we can observe up to
30% CPU time spent by lookup_ioctx:

 32.51%  [guest.kernel]  [g] lookup_ioctx
  9.19%  [guest.kernel]  [g] __lock_acquire.isra.28
  4.40%  [guest.kernel]  [g] lock_release
  4.19%  [guest.kernel]  [g] sched_clock_local
  3.86%  [guest.kernel]  [g] local_clock
  3.68%  [guest.kernel]  [g] native_sched_clock
  3.08%  [guest.kernel]  [g] sched_clock_cpu
  2.64%  [guest.kernel]  [g] lock_release_holdtime.part.11
  2.60%  [guest.kernel]  [g] memcpy
  2.33%  [guest.kernel]  [g] lock_acquired
  2.25%  [guest.kernel]  [g] lock_acquire
  1.84%  [guest.kernel]  [g] do_io_submit

This patchs converts the ioctx list to a radix tree. For a performance
comparison the above FIO script was run on a 2 sockets 8 core
machine. This are the results for the original list based
implementation and for the radix tree based implementation:

cores         1         2         4         8         16        32
list        111025 ms  62219 ms  34193 ms  22998 ms  19335 ms  15956 ms
radix        75400 ms  42668 ms  23923 ms  17206 ms  15820 ms  13295 ms
% of radix
relative      68%       69%       70%       75%       82%       83%
to list

To consider the impact of the patch on the typical case of having
only one ctx per process the following FIO script was run:

rw=randrw; size=100m ;directory=/mnt/fio; ioengine=libaio; iodepth=1
blocksize=1024; numjobs=1; thread; loops=100

on the same system and the results are the following:

list        65241 ms
radix       65402 ms
% of radix
relative    100.25%
to list

Cc: Andi Kleen <ak@linux.intel.com>

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
modified for Mako hybrid from LKML

Signed-off-by: Paul Reioux <reioux@gmail.com>