ext4: minor cleanup of ext4_da_reserve_space()

Remove outdated comments and dead code from ext4_da_reserve_space.
Clean up its trace point, and relocate it to make it more useful.

While we're at it, fix a nearby conditional used to determine if
we have a non-bigalloc file system.  It doesn't match usage elsewhere
in the code, and misleadingly suggests that an s_cluster_ratio value
of 0 would be legal.
Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -1261,13 +1261,12 @@ static int ext4_journalled_write_end(struct file *file,
 }
 
 /*
- * Reserve a single cluster located at lblock
+ * Reserve space for a single cluster
  */
-static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
+static int ext4_da_reserve_space(struct inode *inode)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	struct ext4_inode_info *ei = EXT4_I(inode);
-	unsigned int md_needed;
 	int ret;
 
 	/*
@@ -1279,25 +1278,14 @@ static int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
 	if (ret)
 		return ret;
 
-	/*
-	 * recalculate the amount of metadata blocks to reserve
-	 * in order to allocate nrblocks
-	 * worse case is one extent per block
-	 */
 	spin_lock(&ei->i_block_reservation_lock);
-	/*
-	 * ext4_calc_metadata_amount() has side effects, which we have
-	 * to be prepared undo if we fail to claim space.
-	 */
-	md_needed = 0;
-	trace_ext4_da_reserve_space(inode, 0);
-
 	if (ext4_claim_free_clusters(sbi, 1, 0)) {
 		spin_unlock(&ei->i_block_reservation_lock);
 		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
 		return -ENOSPC;
 	}
 	ei->i_reserved_data_blocks++;
+	trace_ext4_da_reserve_space(inode);
 	spin_unlock(&ei->i_block_reservation_lock);
 
 	return 0;       /* success */
@@ -1566,9 +1554,9 @@ static int ext4_da_map_blocks(struct inode *inode, sector_t iblock,
 		 * then we don't need to reserve it again. However we still need
 		 * to reserve metadata for every block we're going to write.
 		 */
-		if (EXT4_SB(inode->i_sb)->s_cluster_ratio <= 1 ||
+		if (EXT4_SB(inode->i_sb)->s_cluster_ratio == 1 ||
 		    !ext4_find_delalloc_cluster(inode, map->m_lblk)) {
-			ret = ext4_da_reserve_space(inode, iblock);
+			ret = ext4_da_reserve_space(inode);
 			if (ret) {
 				/* not enough space to reserve */
 				retval = ret;

include/trace/events/ext4.h

@@ -1185,15 +1185,14 @@ TRACE_EVENT(ext4_da_update_reserve_space,
 );
 
 TRACE_EVENT(ext4_da_reserve_space,
-	TP_PROTO(struct inode *inode, int md_needed),
+	TP_PROTO(struct inode *inode),
 
-	TP_ARGS(inode, md_needed),
+	TP_ARGS(inode),
 
 	TP_STRUCT__entry(
 		__field(	dev_t,	dev			)
 		__field(	ino_t,	ino			)
 		__field(	__u64,	i_blocks		)
-		__field(	int,	md_needed		)
 		__field(	int,	reserved_data_blocks	)
 		__field(	int,	reserved_meta_blocks	)
 		__field(	__u16,  mode			)
@@ -1203,18 +1202,17 @@ TRACE_EVENT(ext4_da_reserve_space,
 		__entry->dev	= inode->i_sb->s_dev;
 		__entry->ino	= inode->i_ino;
 		__entry->i_blocks = inode->i_blocks;
-		__entry->md_needed = md_needed;
 		__entry->reserved_data_blocks = EXT4_I(inode)->i_reserved_data_blocks;
 		__entry->reserved_meta_blocks = EXT4_I(inode)->i_reserved_meta_blocks;
 		__entry->mode	= inode->i_mode;
 	),
 
-	TP_printk("dev %d,%d ino %lu mode 0%o i_blocks %llu md_needed %d "
+	TP_printk("dev %d,%d ino %lu mode 0%o i_blocks %llu "
 		  "reserved_data_blocks %d reserved_meta_blocks %d",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
 		  (unsigned long) __entry->ino,
 		  __entry->mode, __entry->i_blocks,
-		  __entry->md_needed, __entry->reserved_data_blocks,
+		  __entry->reserved_data_blocks,
 		  __entry->reserved_meta_blocks)
 );