Btrfs: Improve FL_KEEP_SIZE handling in fallocate

- We call inode_size_ok() only if FL_KEEP_SIZE isn't specified.
- As an optimisation we can skip the call if (off + len)
  isn't greater than the current size of the file. This operation
  is called under the lock so the less work we do, the better.
- If we call inode_size_ok() pass to it the correct value rather
  than a more conservative estimation.

Signed-off-by: Davide Italiano <dccitaliano@gmail.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 15a09cb156ce..7af1abda68d0 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2682,9 +2682,12 @@ static long btrfs_fallocate(struct file *file, int mode,
                 return ret;
 
         inode_lock(inode);
-        ret = inode_newsize_ok(inode, alloc_end);
-        if (ret)
-                goto out;
+
+        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size) {
+                ret = inode_newsize_ok(inode, offset + len);
+                if (ret)
+                        goto out;
+        }
 
         /*
          * TODO: Move these two operations after we have checked