Btrfs: Fine tune the btree writeback exclusion some more

Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

@@ -214,6 +214,10 @@ static int btree_writepages(struct address_space *mapping,
 		u64 num_dirty;
 		u64 start = 0;
 		unsigned long thresh = 96 * 1024 * 1024;
+
+		if (wbc->for_kupdate)
+			return 0;
+
 		num_dirty = count_range_bits(tree, &start, thresh, EXTENT_DIRTY);
 		if (num_dirty < thresh) {
 			return 0;

fs/btrfs/file.c

@@ -767,6 +767,7 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
 		num_written += write_bytes;
 
 		balance_dirty_pages_ratelimited_nr(inode->i_mapping, num_pages);
+		if (num_pages < (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
 			btrfs_btree_balance_dirty(root, 1);
 		cond_resched();
 	}