Btrfs: do not needlessly restart the transaction for enospc

We will stop and restart a transaction every time we move to a different leaf
when truncating a file.  This is for enospc reasons, but really we could
probably get away with doing this a little better by actually working until we
hit an ENOSPC.  So add a ->failfast flag to the block_rsv and set it when we do
truncates which will fail as soon as the block rsv runs out of space, and then
at that point we can stop and restart the transaction and refill the block rsv
and carry on.  This will make rm'ing of a file with lots of extents a bit
faster.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ctree.h

@@ -1034,6 +1034,7 @@ struct btrfs_block_rsv {
 	struct btrfs_space_info *space_info;
 	spinlock_t lock;
 	unsigned int full;
+	unsigned int failfast;
 };
 
 /*

fs/btrfs/extent-tree.c

@@ -6308,7 +6308,7 @@ use_block_rsv(struct btrfs_trans_handle *trans,
 	ret = block_rsv_use_bytes(block_rsv, blocksize);
 	if (!ret)
 		return block_rsv;
-	if (ret) {
+	if (ret && !block_rsv->failfast) {
 		static DEFINE_RATELIMIT_STATE(_rs,
 				DEFAULT_RATELIMIT_INTERVAL,
 				/*DEFAULT_RATELIMIT_BURST*/ 2);

fs/btrfs/inode.c

@@ -3448,12 +3448,6 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 
 		if (path->slots[0] == 0 ||
 		    path->slots[0] != pending_del_slot) {
-			if (root->ref_cows &&
-			    BTRFS_I(inode)->location.objectid !=
-						BTRFS_FREE_INO_OBJECTID) {
-				err = -EAGAIN;
-				goto out;
-			}
 			if (pending_del_nr) {
 				ret = btrfs_del_items(trans, root, path,
 						pending_del_slot,
@@ -3826,6 +3820,7 @@ void btrfs_evict_inode(struct inode *inode)
 		goto no_delete;
 	}
 	rsv->size = min_size;
+	rsv->failfast = 1;
 	global_rsv = &root->fs_info->global_block_rsv;
 
 	btrfs_i_size_write(inode, 0);
@@ -3870,7 +3865,7 @@ void btrfs_evict_inode(struct inode *inode)
 		trans->block_rsv = rsv;
 
 		ret = btrfs_truncate_inode_items(trans, root, inode, 0, 0);
-		if (ret != -EAGAIN)
+		if (ret != -ENOSPC)
 			break;
 
 		nr = trans->blocks_used;
@@ -6852,6 +6847,7 @@ static int btrfs_truncate(struct inode *inode)
 	if (!rsv)
 		return -ENOMEM;
 	rsv->size = min_size;
+	rsv->failfast = 1;
 
 	/*
 	 * 1 for the truncate slack space
@@ -6905,37 +6901,13 @@ static int btrfs_truncate(struct inode *inode)
 	 * safe.
 	 */
 	set_bit(BTRFS_INODE_NEEDS_FULL_SYNC, &BTRFS_I(inode)->runtime_flags);
+	trans->block_rsv = rsv;
 
 	while (1) {
-		ret = btrfs_block_rsv_refill(root, rsv, min_size);
-		if (ret) {
-			/*
-			 * This can only happen with the original transaction we
-			 * started above, every other time we shouldn't have a
-			 * transaction started yet.
-			 */
-			if (ret == -EAGAIN)
-				goto end_trans;
-			err = ret;
-			break;
-		}
-
-		if (!trans) {
-			/* Just need the 1 for updating the inode */
-			trans = btrfs_start_transaction(root, 1);
-			if (IS_ERR(trans)) {
-				ret = err = PTR_ERR(trans);
-				trans = NULL;
-				break;
-			}
-		}
-
-		trans->block_rsv = rsv;
-
 		ret = btrfs_truncate_inode_items(trans, root, inode,
 						 inode->i_size,
 						 BTRFS_EXTENT_DATA_KEY);
-		if (ret != -EAGAIN) {
+		if (ret != -ENOSPC) {
 			err = ret;
 			break;
 		}
@@ -6946,11 +6918,22 @@ static int btrfs_truncate(struct inode *inode)
 			err = ret;
 			break;
 		}
-end_trans:
+
 		nr = trans->blocks_used;
 		btrfs_end_transaction(trans, root);
-		trans = NULL;
 		btrfs_btree_balance_dirty(root, nr);
+
+		trans = btrfs_start_transaction(root, 2);
+		if (IS_ERR(trans)) {
+			ret = err = PTR_ERR(trans);
+			trans = NULL;
+			break;
+		}
+
+		ret = btrfs_block_rsv_migrate(&root->fs_info->trans_block_rsv,
+					      rsv, min_size);
+		BUG_ON(ret);	/* shouldn't happen */
+		trans->block_rsv = rsv;
 	}
 
 	if (ret == 0 && inode->i_nlink > 0) {