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 <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 82d0342763c5..c77da440146a 100644
--- a/fs/btrfs/file.c
+++ b/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;