On Tue, Aug 12, 2008 at 09:27:53AM -0700, Mingming Cao wrote:

....
....

 /*
- * ext4_ext_calc_credits_for_insert:
- * This routine returns max. credits that the extent tree can consume.
- * It should be OK for low-performance paths like ->writepage()
- * To allow many writing processes to fit into a single transaction,
- * the caller should calculate credits under i_data_sem and
- * pass the actual path.
+ * ext4_ext_calc_credits_for_single_extent:
+ * This routine returns max. credits that needed to insert an extent
+ * to the extent tree.
+ * When pass the actual path, the caller should calculate credits
+ * under i_data_sem.
  */
-int ext4_ext_calc_credits_for_insert(struct inode *inode,
+int ext4_ext_calc_credits_for_single_extent(struct inode *inode, int num,
 						struct ext4_ext_path *path)
 {
-	int depth, needed;
+	int depth = ext_depth(inode);

 	if (path) {
 		/* probably there is space in leaf? */
-		depth = ext_depth(inode);
 		if (le16_to_cpu(path[depth].p_hdr->eh_entries)
 				< le16_to_cpu(path[depth].p_hdr->eh_max))
-			return 1;
+			return 2 + EXT4_META_TRANS_BLOCKS(inode->i_sb);
 	}

-	/*
-	 * given 32-bit logical block (4294967296 blocks), max. tree
-	 * can be 4 levels in depth -- 4 * 340^4 == 53453440000.
-	 * Let's also add one more level for imbalance.
-	 */
-	depth = 5;
-
-	/* allocation of new data block(s) */
-	needed = 2;
+	return ext4_ext_writepage_trans_blocks(inode, num, 1);

single extent insert should not look at journaling mode or not
In the above with path specified we don't look at journaling mode
but ext4_ext_writepage_trans_blocks will do

+}

-	/*
-	 * tree can be full, so it would need to grow in depth:
-	 * we need one credit to modify old root, credits for
-	 * new root will be added in split accounting
-	 */
-	needed += 1;
+/*
+ * How many index/leaf blocks need to change/allocate to modify nrblocks?
+ *
+ * if nrblocks are fit in a single extent (chunk flag is 1), then
+ * in the worse case, each tree level index/leaf need to be changed
+ * if the tree split due to insert a new extent, then the old tree
+ * index/leaf need to be updated too
+ *
+ * If the nrblocks are discontigous, they could cause
+ * the whole tree split more than once, but this is really rare.
+ */
+static int ext4_ext_index_trans_blocks(struct inode *inode, int num, int chunk)
+{
+	int index;
+	int depth = ext_depth(inode);

-	/*
-	 * Index split can happen, we would need:
-	 *    allocate intermediate indexes (bitmap + group)
-	 *  + change two blocks at each level, but root (already included)
-	 */
-	needed += (depth * 2) + (depth * 2);

-	/* any allocation modifies superblock */
-	needed += 1;
+	if (chunk)
+		index = depth * 2;
+	else
+		index = depth * 3;

-	return needed;
+	return index;
 }

....

-aneesh