Btrfs: incompatible format change to remove hole extents

Btrfs has always had these filler extent data items for holes in inodes.  This
has made somethings very easy, like logging hole punches and sending hole
punches.  However for large holey files these extent data items are pure
overhead.  So add an incompatible feature to no longer add hole extents to
reduce the amount of metadata used by these sort of files.  This has a few
changes for logging and send obviously since they will need to detect holes and
log/send the holes if there are any.  I've tested this thoroughly with xfstests
and it doesn't cause any issues with and without the incompat format set.
Thanks,

Signed-off-by: Josef Bacik <[email protected]>
Signed-off-by: Chris Mason <[email protected]>

Author: Josef Bacik

fs/btrfs/ctree.c

@@ -41,7 +41,6 @@ static void del_ptr(struct btrfs_root *root, struct btrfs_path *path,
 		    int level, int slot);
 static void tree_mod_log_free_eb(struct btrfs_fs_info *fs_info,
 				 struct extent_buffer *eb);
-static int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path);
 
 struct btrfs_path *btrfs_alloc_path(void)
 {
@@ -4817,7 +4816,7 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
  * This may release the path, and so you may lose any locks held at the
  * time you call it.
  */
-static int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path)
+int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path)
 {
 	struct btrfs_key key;
 	struct btrfs_disk_key found_key;

fs/btrfs/ctree.h

@@ -521,6 +521,7 @@ struct btrfs_super_block {
 #define BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF	(1ULL << 6)
 #define BTRFS_FEATURE_INCOMPAT_RAID56		(1ULL << 7)
 #define BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA	(1ULL << 8)
+#define BTRFS_FEATURE_INCOMPAT_NO_HOLES		(1ULL << 9)
 
 #define BTRFS_FEATURE_COMPAT_SUPP		0ULL
 #define BTRFS_FEATURE_COMPAT_RO_SUPP		0ULL
@@ -532,7 +533,8 @@ struct btrfs_super_block {
 	 BTRFS_FEATURE_INCOMPAT_COMPRESS_LZO |		\
 	 BTRFS_FEATURE_INCOMPAT_RAID56 |		\
 	 BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF |		\
-	 BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA)
+	 BTRFS_FEATURE_INCOMPAT_SKINNY_METADATA |	\
+	 BTRFS_FEATURE_INCOMPAT_NO_HOLES)
 
 /*
  * A leaf is full of items. offset and size tell us where to find
@@ -3399,6 +3401,7 @@ static inline int btrfs_insert_empty_item(struct btrfs_trans_handle *trans,
 }
 
 int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path);
+int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path);
 int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
 			u64 time_seq);
 static inline int btrfs_next_old_item(struct btrfs_root *root,

fs/btrfs/file.c

@@ -1963,11 +1963,13 @@ static int fill_holes(struct btrfs_trans_handle *trans, struct inode *inode,
 	struct btrfs_key key;
 	int ret;
 
+	if (btrfs_fs_incompat(root->fs_info, NO_HOLES))
+		goto out;
+
 	key.objectid = btrfs_ino(inode);
 	key.type = BTRFS_EXTENT_DATA_KEY;
 	key.offset = offset;
 
-
 	ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
 	if (ret < 0)
 		return ret;
@@ -2064,8 +2066,10 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 	u64 drop_end;
 	int ret = 0;
 	int err = 0;
+	int rsv_count;
 	bool same_page = ((offset >> PAGE_CACHE_SHIFT) ==
 			  ((offset + len - 1) >> PAGE_CACHE_SHIFT));
+	bool no_holes = btrfs_fs_incompat(root->fs_info, NO_HOLES);
 
 	ret = btrfs_wait_ordered_range(inode, offset, len);
 	if (ret)
@@ -2163,9 +2167,10 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 	/*
 	 * 1 - update the inode
 	 * 1 - removing the extents in the range
-	 * 1 - adding the hole extent
+	 * 1 - adding the hole extent if no_holes isn't set
 	 */
-	trans = btrfs_start_transaction(root, 3);
+	rsv_count = no_holes ? 2 : 3;
+	trans = btrfs_start_transaction(root, rsv_count);
 	if (IS_ERR(trans)) {
 		err = PTR_ERR(trans);
 		goto out_free;
@@ -2202,7 +2207,7 @@ static int btrfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
 		btrfs_end_transaction(trans, root);
 		btrfs_btree_balance_dirty(root);
 
-		trans = btrfs_start_transaction(root, 3);
+		trans = btrfs_start_transaction(root, rsv_count);
 		if (IS_ERR(trans)) {
 			ret = PTR_ERR(trans);
 			trans = NULL;

fs/btrfs/inode.c

@@ -4203,6 +4203,49 @@ int btrfs_truncate_page(struct inode *inode, loff_t from, loff_t len,
 	return ret;
 }
 
+static int maybe_insert_hole(struct btrfs_root *root, struct inode *inode,
+			     u64 offset, u64 len)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	/*
+	 * Still need to make sure the inode looks like it's been updated so
+	 * that any holes get logged if we fsync.
+	 */
+	if (btrfs_fs_incompat(root->fs_info, NO_HOLES)) {
+		BTRFS_I(inode)->last_trans = root->fs_info->generation;
+		BTRFS_I(inode)->last_sub_trans = root->log_transid;
+		BTRFS_I(inode)->last_log_commit = root->last_log_commit;
+		return 0;
+	}
+
+	/*
+	 * 1 - for the one we're dropping
+	 * 1 - for the one we're adding
+	 * 1 - for updating the inode.
+	 */
+	trans = btrfs_start_transaction(root, 3);
+	if (IS_ERR(trans))
+		return PTR_ERR(trans);
+
+	ret = btrfs_drop_extents(trans, root, inode, offset, offset + len, 1);
+	if (ret) {
+		btrfs_abort_transaction(trans, root, ret);
+		btrfs_end_transaction(trans, root);
+		return ret;
+	}
+
+	ret = btrfs_insert_file_extent(trans, root, btrfs_ino(inode), offset,
+				       0, 0, len, 0, len, 0, 0, 0);
+	if (ret)
+		btrfs_abort_transaction(trans, root, ret);
+	else
+		btrfs_update_inode(trans, root, inode);
+	btrfs_end_transaction(trans, root);
+	return ret;
+}
+
 /*
  * This function puts in dummy file extents for the area we're creating a hole
  * for.  So if we are truncating this file to a larger size we need to insert
@@ -4211,7 +4254,6 @@ int btrfs_truncate_page(struct inode *inode, loff_t from, loff_t len,
  */
 int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size)
 {
-	struct btrfs_trans_handle *trans;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
 	struct extent_map *em = NULL;
@@ -4266,31 +4308,10 @@ int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size)
 			struct extent_map *hole_em;
 			hole_size = last_byte - cur_offset;
 
-			trans = btrfs_start_transaction(root, 3);
-			if (IS_ERR(trans)) {
-				err = PTR_ERR(trans);
-				break;
-			}
-
-			err = btrfs_drop_extents(trans, root, inode,
-						 cur_offset,
-						 cur_offset + hole_size, 1);
-			if (err) {
-				btrfs_abort_transaction(trans, root, err);
-				btrfs_end_transaction(trans, root);
-				break;
-			}
-
-			err = btrfs_insert_file_extent(trans, root,
-					btrfs_ino(inode), cur_offset, 0,
-					0, hole_size, 0, hole_size,
-					0, 0, 0);
-			if (err) {
-				btrfs_abort_transaction(trans, root, err);
-				btrfs_end_transaction(trans, root);
+			err = maybe_insert_hole(root, inode, cur_offset,
+						hole_size);
+			if (err)
 				break;
-			}
-
 			btrfs_drop_extent_cache(inode, cur_offset,
 						cur_offset + hole_size - 1, 0);
 			hole_em = alloc_extent_map();
@@ -4309,7 +4330,7 @@ int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size)
 			hole_em->ram_bytes = hole_size;
 			hole_em->bdev = root->fs_info->fs_devices->latest_bdev;
 			hole_em->compress_type = BTRFS_COMPRESS_NONE;
-			hole_em->generation = trans->transid;
+			hole_em->generation = root->fs_info->generation;
 
 			while (1) {
 				write_lock(&em_tree->lock);
@@ -4322,17 +4343,14 @@ int btrfs_cont_expand(struct inode *inode, loff_t oldsize, loff_t size)
 							hole_size - 1, 0);
 			}
 			free_extent_map(hole_em);
-next:
-			btrfs_update_inode(trans, root, inode);
-			btrfs_end_transaction(trans, root);
 		}
+next:
 		free_extent_map(em);
 		em = NULL;
 		cur_offset = last_byte;
 		if (cur_offset >= block_end)
 			break;
 	}
-
 	free_extent_map(em);
 	unlock_extent_cached(io_tree, hole_start, block_end - 1, &cached_state,
 			     GFP_NOFS);