Btrfs: don't use global block reservation for inode cache truncation

It is very likely that there are lots of subvolumes/snapshots in the filesystem,
so if we use global block reservation to do inode cache truncation, we may hog
all the free space that is reserved in global rsv. So it is better that we do
the free space reservation for inode cache truncation by ourselves.

Cc: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/extent-tree.c

@@ -3106,6 +3106,11 @@ static int cache_save_setup(struct btrfs_block_group_cache *block_group,
 	WARN_ON(ret);
 
 	if (i_size_read(inode) > 0) {
+		ret = btrfs_check_trunc_cache_free_space(root,
+					&root->fs_info->global_block_rsv);
+		if (ret)
+			goto out_put;
+
 		ret = btrfs_truncate_free_space_cache(root, trans, path,
 						      inode);
 		if (ret)

fs/btrfs/free-space-cache.c

@@ -197,30 +197,32 @@ int create_free_space_inode(struct btrfs_root *root,
 					 block_group->key.objectid);
 }
 
-int btrfs_truncate_free_space_cache(struct btrfs_root *root,
-				    struct btrfs_trans_handle *trans,
-				    struct btrfs_path *path,
-				    struct inode *inode)
+int btrfs_check_trunc_cache_free_space(struct btrfs_root *root,
+				       struct btrfs_block_rsv *rsv)
 {
-	struct btrfs_block_rsv *rsv;
 	u64 needed_bytes;
-	loff_t oldsize;
-	int ret = 0;
-
-	rsv = trans->block_rsv;
-	trans->block_rsv = &root->fs_info->global_block_rsv;
+	int ret;
 
 	/* 1 for slack space, 1 for updating the inode */
 	needed_bytes = btrfs_calc_trunc_metadata_size(root, 1) +
 		btrfs_calc_trans_metadata_size(root, 1);
 
-	spin_lock(&trans->block_rsv->lock);
-	if (trans->block_rsv->reserved < needed_bytes) {
-		spin_unlock(&trans->block_rsv->lock);
-		trans->block_rsv = rsv;
-		return -ENOSPC;
-	}
-	spin_unlock(&trans->block_rsv->lock);
+	spin_lock(&rsv->lock);
+	if (rsv->reserved < needed_bytes)
+		ret = -ENOSPC;
+	else
+		ret = 0;
+	spin_unlock(&rsv->lock);
+	return 0;
+}
+
+int btrfs_truncate_free_space_cache(struct btrfs_root *root,
+				    struct btrfs_trans_handle *trans,
+				    struct btrfs_path *path,
+				    struct inode *inode)
+{
+	loff_t oldsize;
+	int ret = 0;
 
 	oldsize = i_size_read(inode);
 	btrfs_i_size_write(inode, 0);
@@ -232,17 +234,14 @@ int btrfs_truncate_free_space_cache(struct btrfs_root *root,
 	 */
 	ret = btrfs_truncate_inode_items(trans, root, inode,
 					 0, BTRFS_EXTENT_DATA_KEY);
-
 	if (ret) {
-		trans->block_rsv = rsv;
 		btrfs_abort_transaction(trans, root, ret);
 		return ret;
 	}
 
 	ret = btrfs_update_inode(trans, root, inode);
 	if (ret)
 		btrfs_abort_transaction(trans, root, ret);
-	trans->block_rsv = rsv;
 
 	return ret;
 }

fs/btrfs/free-space-cache.h

@@ -54,6 +54,8 @@ int create_free_space_inode(struct btrfs_root *root,
 			    struct btrfs_block_group_cache *block_group,
 			    struct btrfs_path *path);
 
+int btrfs_check_trunc_cache_free_space(struct btrfs_root *root,
+				       struct btrfs_block_rsv *rsv);
 int btrfs_truncate_free_space_cache(struct btrfs_root *root,
 				    struct btrfs_trans_handle *trans,
 				    struct btrfs_path *path,

fs/btrfs/inode-map.c

@@ -429,11 +429,12 @@ int btrfs_save_ino_cache(struct btrfs_root *root,
 	num_bytes = trans->bytes_reserved;
 	/*
 	 * 1 item for inode item insertion if need
-	 * 3 items for inode item update (in the worst case)
+	 * 4 items for inode item update (in the worst case)
+	 * 1 items for slack space if we need do truncation
 	 * 1 item for free space object
 	 * 3 items for pre-allocation
 	 */
-	trans->bytes_reserved = btrfs_calc_trans_metadata_size(root, 8);
+	trans->bytes_reserved = btrfs_calc_trans_metadata_size(root, 10);
 	ret = btrfs_block_rsv_add(root, trans->block_rsv,
 				  trans->bytes_reserved,
 				  BTRFS_RESERVE_NO_FLUSH);

fs/btrfs/relocation.c

@@ -3350,6 +3350,11 @@ static int delete_block_group_cache(struct btrfs_fs_info *fs_info,
 	}
 
 truncate:
+	ret = btrfs_check_trunc_cache_free_space(root,
+						 &fs_info->global_block_rsv);
+	if (ret)
+		goto out;
+
 	path = btrfs_alloc_path();
 	if (!path) {
 		ret = -ENOMEM;