btrfs: allocate btrfs_inode::file_extent_tree only without NO_HOLES

The file_extent_tree was added in 41a2ee75aab0 ("btrfs: introduce
per-inode file extent tree") so we have an explicit mapping of the file
extents to know where it is safe to update i_size. When the feature
NO_HOLES is enabled, and it's been a mkfs default since 5.15, the tree
is not necessary.

To save some space in the inode, allocate the tree only when necessary.
This reduces size by 16 bytes from 1096 to 1080 on a x86_64 release
config.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 20 insertions, 5 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e79a047aa5d1..38adab92a015 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8479,10 +8479,20 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
 	struct btrfs_inode *ei;
 	struct inode *inode;
+	struct extent_io_tree *file_extent_tree = NULL;
+
+	/* Self tests may pass a NULL fs_info. */
+	if (fs_info && !btrfs_fs_incompat(fs_info, NO_HOLES)) {
+		file_extent_tree = kmalloc(sizeof(struct extent_io_tree), GFP_KERNEL);
+		if (!file_extent_tree)
+			return NULL;
+	}
 
 	ei = alloc_inode_sb(sb, btrfs_inode_cachep, GFP_KERNEL);
-	if (!ei)
+	if (!ei) {
+		kfree(file_extent_tree);
 		return NULL;
+	}
 
 	ei->root = NULL;
 	ei->generation = 0;
@@ -8523,10 +8533,13 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 	extent_io_tree_init(fs_info, &ei->io_tree, IO_TREE_INODE_IO);
 	ei->io_tree.inode = ei;
 
-	extent_io_tree_init(fs_info, &ei->file_extent_tree,
-			    IO_TREE_INODE_FILE_EXTENT);
-	/* Lockdep class is set only for the file extent tree. */
-	lockdep_set_class(&ei->file_extent_tree.lock, &file_extent_tree_class);
+	ei->file_extent_tree = file_extent_tree;
+	if (file_extent_tree) {
+		extent_io_tree_init(fs_info, ei->file_extent_tree,
+				    IO_TREE_INODE_FILE_EXTENT);
+		/* Lockdep class is set only for the file extent tree. */
+		lockdep_set_class(&ei->file_extent_tree->lock, &file_extent_tree_class);
+	}
 	mutex_init(&ei->log_mutex);
 	spin_lock_init(&ei->ordered_tree_lock);
 	ei->ordered_tree = RB_ROOT;
@@ -8543,12 +8556,14 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 void btrfs_test_destroy_inode(struct inode *inode)
 {
 	btrfs_drop_extent_map_range(BTRFS_I(inode), 0, (u64)-1, false);
+	kfree(BTRFS_I(inode)->file_extent_tree);
 	kmem_cache_free(btrfs_inode_cachep, BTRFS_I(inode));
 }
 #endif
 
 void btrfs_free_inode(struct inode *inode)
 {
+	kfree(BTRFS_I(inode)->file_extent_tree);
 	kmem_cache_free(btrfs_inode_cachep, BTRFS_I(inode));
 }