Btrfs: fix data allocation hint start
Sometimes our start allocation hint when we cow a file can be either
EXTENT_HOLE or some other such place holder, which is not optimal. So if we
find that our em->block_start is one of these special values, check to see
where the first block of the inode is stored, and use that as a hint. If that
block is also a special value, just fallback on a hint of 0 and let the
allocator figure out a good place to put the data.
Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 78139ef..d8393dd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -743,8 +743,22 @@
em = search_extent_mapping(&BTRFS_I(inode)->extent_tree,
start, num_bytes);
if (em) {
- alloc_hint = em->block_start;
- free_extent_map(em);
+ /*
+ * if block start isn't an actual block number then find the
+ * first block in this inode and use that as a hint. If that
+ * block is also bogus then just don't worry about it.
+ */
+ if (em->block_start >= EXTENT_MAP_LAST_BYTE) {
+ free_extent_map(em);
+ em = search_extent_mapping(em_tree, 0, 0);
+ if (em && em->block_start < EXTENT_MAP_LAST_BYTE)
+ alloc_hint = em->block_start;
+ if (em)
+ free_extent_map(em);
+ } else {
+ alloc_hint = em->block_start;
+ free_extent_map(em);
+ }
}
read_unlock(&BTRFS_I(inode)->extent_tree.lock);
btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);