Btrfs: fix merge delalloc logic

My patch to properly count outstanding extents wrt MAX_EXTENT_SIZE introduced a
regression when re-dirtying already dirty areas.  We have logic in split to make
sure we are taking the largest space into account but didn't have it for merge,
so it was sometimes making us think we were turning a tiny extent into a huge
extent, when in reality we already had a huge extent and needed to use the other
side in our logic.  This fixes the regression that was reported by a user on
list.  Thanks,

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 91a87f53be3c1d1498430d2ace956cfe6dcc737b..97b601bec326bc09a885c0f55ad29647a88790c6 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1592,7 +1592,12 @@ static void btrfs_merge_extent_hook(struct inode *inode,
                return;
 
        old_size = other->end - other->start + 1;
-       new_size = old_size + (new->end - new->start + 1);
+       if (old_size < (new->end - new->start + 1))
+               old_size = (new->end - new->start + 1);
+       if (new->start > other->start)
+               new_size = new->end - other->start + 1;
+       else
+               new_size = other->end - new->start + 1;
 
        /* we're not bigger than the max, unreserve the space and go */
        if (new_size <= BTRFS_MAX_EXTENT_SIZE) {