The following commit has been merged in the linux branch: commit 444528b3e614f7f2391488d9bca8e0b872db909b Author: Chris Mason chris.mason@oracle.com Date: Wed Oct 14 09:38:28 2009 -0400
Btrfs: always pin metadata in discard mode
We have an optimization in btrfs to allow blocks to be immediately freed if they were allocated in this transaction and never written. Otherwise they are pinned and freed when the transaction commits.
This isn't optimal for discard mode because immediately freeing them means immediately discarding them. It is better to give the block to the pinning code and letting the (slow) discard happen later.
Signed-off-by: Chris Mason chris.mason@oracle.com
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index d4a3528..c56f916 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -3686,6 +3686,14 @@ static int pin_down_bytes(struct btrfs_trans_handle *trans, if (is_data) goto pinit;
+ /* + * discard is sloooow, and so triggering discards on + * individual btree blocks isn't a good plan. Just + * pin everything in discard mode. + */ + if (btrfs_test_opt(root, DISCARD)) + goto pinit; + buf = btrfs_find_tree_block(root, bytenr, num_bytes); if (!buf) goto pinit;