[PATCH v2 2/3] btrfs: inode: Cleanup the log tree exceptions in btrfs_truncate_inode_items()

[Qu Wenruo <wqu@suse.com>]

There are a lot of root owner check in btrfs_truncate_inode_items()
like:

	if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) ||
	    root == fs_info->tree_root)

But considering that, there are only those trees can have INODE_ITEMs:
- tree root (For v1 space cache)
- subvolume trees
- tree reloc trees
- data reloc tree
- log trees

And since subvolume/tree reloc/data reloc trees all have SHAREABLE bit,
and we're checking tree root manually, so above check is just excluding
log trees.

This patch will replace two of such checks to a much simpler one:

	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID)

This would merge btrfs_drop_extent_cache() and lock_extent_bits() call
into the same if branch.

Also since we're here, add one comment explaining why we don't want to
call lock_extent_bits()/drop_extent_cache() on log trees.

Finally replace ALIGN()/ALIGN_DOWN() to round_up()/round_down(), as I'm
always bad at determing the alignement direction.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a6c26c10ffc5..771af55038bf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4101,7 +4101,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 	u64 bytes_deleted = 0;
 	bool be_nice = false;
 	bool should_throttle = false;
-	const u64 lock_start = ALIGN_DOWN(new_size, fs_info->sectorsize);
+	const u64 lock_start = round_down(new_size, fs_info->sectorsize);
 	struct extent_state *cached_state = NULL;
 
 	BUG_ON(new_size > 0 && min_type != BTRFS_EXTENT_DATA_KEY);
@@ -4121,20 +4121,22 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 	path->reada = READA_BACK;
 
-	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID)
-		lock_extent_bits(&BTRFS_I(inode)->io_tree, lock_start, (u64)-1,
-				 &cached_state);
-
 	/*
-	 * We want to drop from the next block forward in case this new size is
-	 * not block aligned since we will be keeping the last block of the
-	 * extent just the way it is.
+	 * There will be a lot of exceptions for log trees, as log inodes are
+	 * not real inodes, but an anchor for logged inodes.
 	 */
-	if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) ||
-	    root == fs_info->tree_root)
-		btrfs_drop_extent_cache(BTRFS_I(inode), ALIGN(new_size,
+	if (root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
+		/*
+		 * We want to drop from the next block forward in case this
+		 * new size is not block aligned since we will be keeping the
+		 * last block of the extent just the way it is.
+		 */
+		lock_extent_bits(&BTRFS_I(inode)->io_tree, lock_start, (u64)-1,
+				 &cached_state);
+		btrfs_drop_extent_cache(BTRFS_I(inode), round_up(new_size,
 					fs_info->sectorsize),
 					(u64)-1, 0);
+	}
 
 	/*
 	 * This function is also used to drop the items in the log tree before
@@ -4335,8 +4337,7 @@ int btrfs_truncate_inode_items(struct btrfs_trans_handle *trans,
 		should_throttle = false;
 
 		if (found_extent &&
-		    (test_bit(BTRFS_ROOT_SHAREABLE, &root->state) ||
-		     root == fs_info->tree_root)) {
+		    root->root_key.objectid != BTRFS_TREE_LOG_OBJECTID) {
 			struct btrfs_ref ref = { 0 };
 
 			bytes_deleted += extent_num_bytes;
-- 
2.26.2