ocfs2: Optimize inode group allocation by recording last used group.

In ocfs2, the block group search looks for the "emptiest" group
to allocate from. So if the allocator has many equally(or almost
equally) empty groups, new block group will tend to get spread
out amongst them.

So we add osb_inode_alloc_group in ocfs2_super to record the last
used inode allocation group.
For more details, please see
http://oss.oracle.com/osswiki/OCFS2/DesignDocs/InodeAllocationStrategy.

I have done some basic test and the results are a ten times improvement on
some cold-cache stat workloads.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
index e1844d5736c4..b65d19c9756d 100644
--- a/fs/ocfs2/ocfs2.h
+++ b/fs/ocfs2/ocfs2.h
@@ -343,6 +343,9 @@ struct ocfs2_super
 
         unsigned int                    osb_dx_mask;
         u32                             osb_dx_seed[4];
+
+        /* the group we used to allocate inodes. */
+        u64                             osb_inode_alloc_group;
 };
 
 #define OCFS2_SB(sb)        ((struct ocfs2_super *)(sb)->s_fs_info)