[GFS2] gfs2_alloc_required performance

This is a small I/O performance enhancement to gfs2.  (Actually, it is a rework of
an earlier version I got wrong).  The idea here is to check if the write extends
past the last block in the file.  If so, the function can save itself a lot of
time and trouble because it knows an allocate will be required.  Benchmarks like
iozone should see better performance.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 73dfad70de66..4356cc2fb3f5 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -1224,6 +1224,11 @@ int gfs2_write_alloc_required(struct gfs2_inode *ip, u64 offset,
                 unsigned int shift = sdp->sd_sb.sb_bsize_shift;
                 lblock = offset >> shift;
                 lblock_stop = (offset + len + sdp->sd_sb.sb_bsize - 1) >> shift;
+                if (lblock_stop > ip->i_di.di_blocks) { /* writing past the
+                                                           last block */
+                        *alloc_required = 1;
+                        return 0;
+                }
         }
 
         for (; lblock < lblock_stop; lblock += extlen) {