ocfs2: change default reservation window sizes

The default reservation size of 4 (32-bit windows) is a bit too ambitious.
Scale it back to 16 bits (resv_level=2). I have been testing various sizes
on a 4-node cluster which runs a mixed workload that is heavily threaded.
With a 256MB local alloc, I get *roughly* the following levels of average file
fragmentation:

resv_level=0	70%
resv_level=1	21%
resv_level=2	23%
resv_level=3	24%
resv_level=4	60%
resv_level=5	did not test
resv_level=6	60%

resv_level=2 seemed like a good compromise between not letting windows be
too small, but not so big that heavier workloads will immediately suffer
without tuning.

This patch also change the behavior of directory reservations - they now
track file reservations.  The previous compromise of giving directory
windows only 8 bits wound up fragmenting more at some window sizes because
file allocations had smaller unused windows to poach from.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/Documentation/filesystems/ocfs2.txt b/Documentation/filesystems/ocfs2.txt
index 412df9095937..32339e584a9a 100644
--- a/Documentation/filesystems/ocfs2.txt
+++ b/Documentation/filesystems/ocfs2.txt
@@ -80,6 +80,6 @@ user_xattr	(*)	Enables Extended User Attributes.
 nouser_xattr            Disables Extended User Attributes.
 acl                     Enables POSIX Access Control Lists support.
 noacl           (*)     Disables POSIX Access Control Lists support.
-resv_level=4    (*)     Set how agressive allocation reservations will be.
+resv_level=2    (*)     Set how agressive allocation reservations will be.
                         Valid values are between 0 (reservations off) to 8
                         (maximum space for reservations).