Btrfs: enforce min_bytes parameter during extent allocation

Commit 24542bf7ea5e4fdfdb5157ff544c093fa4dcb536 changed preallocation of
extents to cap the max size we try to allocate.  It's a valid change,
but the extent reservation code is also used by balance, and that
can't tolerate a smaller extent being allocated.

__btrfs_prealloc_file_range already has a min_size parameter, which is
used by relocation to request a specific extent size.  This commit
adds an extra check to enforce that minimum extent size.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Reported-by: Stefan Behrens <sbehrens@giantdisaster.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index ecd9c4cdb0db..13ab4de0a400 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8502,6 +8502,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
         struct btrfs_key ins;
         u64 cur_offset = start;
         u64 i_size;
+        u64 cur_bytes;
         int ret = 0;
         bool own_trans = true;
 
@@ -8516,8 +8517,9 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
                         }
                 }
 
-                ret = btrfs_reserve_extent(trans, root,
-                                           min(num_bytes, 256ULL * 1024 * 1024),
+                cur_bytes = min(num_bytes, 256ULL * 1024 * 1024);
+                cur_bytes = max(cur_bytes, min_size);
+                ret = btrfs_reserve_extent(trans, root, cur_bytes,
                                            min_size, 0, *alloc_hint, &ins, 1);
                 if (ret) {
                         if (own_trans)