mm: change initial readahead window size calculation

Change the logic which determines the initial readahead window size
such that for small requests (one page) the initial window size
will be x4 the size of the original request, regardless of the
VM_MAX_READAHEAD value. This prevents a rapid ramp-up
that could be caused due to increasing VM_MAX_READAHEAD.

Change-Id: I93d59c515d7e6c6d62348790980ff7bd4f434997
Signed-off-by: Lee Susman <lsusman@codeaurora.org>
block: recursive merge requests

In a workload, thread 1 accesses a, a+2, ..., thread 2 accesses a+1, a+3,....
When the requests are flushed to queue, a and a+1 are merged to (a, a+1), a+2
and a+3 too to (a+2, a+3), but (a, a+1) and (a+2, a+3) aren't merged.

If we do recursive merge for such interleave access, some workloads throughput
get improvement. A recent worload I'm checking on is swap, below change
boostes the throughput around 5% ~ 10%.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
sync: don't block the flusher thread waiting on IO

When sync does it's WB_SYNC_ALL writeback, it issues data Io and
then immediately waits for IO completion. This is done in the
context of the flusher thread, and hence completely ties up the
flusher thread for the backing device until all the dirty inodes
have been synced. On filesystems that are dirtying inodes constantly
and quickly, this means the flusher thread can be tied up for
minutes per sync call and hence badly affect system level write IO
performance as the page cache cannot be cleaned quickly.

We already have a wait loop for IO completion for sync(2), so cut
this out of the flusher thread and delegate it to wait_sb_inodes().
Hence we can do rapid IO submission, and then wait for it all to
complete.

Effect of sync on fsmark before the patch:

FSUse%        Count         Size    Files/sec     App Overhead
.....
     0       640000         4096      35154.6          1026984
     0       720000         4096      36740.3          1023844
     0       800000         4096      36184.6           916599
     0       880000         4096       1282.7          1054367
     0       960000         4096       3951.3           918773
     0      1040000         4096      40646.2           996448
     0      1120000         4096      43610.1           895647
     0      1200000         4096      40333.1           921048

And a single sync pass took:

  real    0m52.407s
  user    0m0.000s
  sys     0m0.090s

After the patch, there is no impact on fsmark results, and each
individual sync(2) operation run concurrently with the same fsmark
workload takes roughly 7s:

  real    0m6.930s
  user    0m0.000s
  sys     0m0.039s

IOWs, sync is 7-8x faster on a busy filesystem and does not have an
adverse impact on ongoing async data write operations.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers: scsi: Kconfig: Don't build as a module
Added BITS_PER_LONG_LONG definition avoiding lib/vsprintf.c errors.

Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>
sync: signal pt before sync_timeline object gets destroyed

There is a race condition

Assume we have *one* sync_fence object, with *one* sync_pt
which belongs to *one* sync_timeline, given this condition,
sync_timeline->kref will have two counts, one for sync_timeline
(implicit) and another for sync_pt.

Assume following is the situation on CPU

Theead-1 : (Thread which calls sync_timeline_destroy())
  -> (some function calls)
   -> sync_timeline_destory()
    -> sync_timeline_signal() (CPU is inside this
function after putting reference to sync_timeline)

At this time Thread-2 comes and does following

Thread-2 : (fclose on fence fd)
> sync_fence_release() -> because of fclose() on fence object
 -> sync_fence_free()
  -> sync_pt_free()
   -> kref_put(&pt->parent->kref, sync_timeline_free);
    -> sync_timeline_free() (CPU is inside this because
this time kref will be zero after _put)

Thread-2 will free sync_timeline object before Thread-1
has finished its work inside sync_timeline_signal.

With this change we signals all sync_pt before putting
reference to sync_timeline object.

Change-Id: Ic680e4d0bbef1c46bcb7cfba693395645241d203
Signed-off-by: Prakash Kamliya <pkamliya@codeaurora.org>
Signed-off-by: Rom Lemarchand <romlem@google.com>
defconfig: don't build scsi_wait_scan at all