[PATCH 2/2] maple tree: Add and fix some comments

[Dev Jain <dev.jain@arm.com>]

Add comments explaining the fields for maple_metadata, since "end" is
ambiguous and "gap" can be confused as the largest gap, whereas it
is actually the offset of the largest gap.

MAPLE_ROOT_NODE is used for mt_mk_root() and mt_safe_root(), indicating
that it is used to mark the node as root. So fix the comment.

Add comment for mas_ascend() to explain, whose min and max we are
trying to find. Explain that, for example, if we are already on offset
zero, then the parent min is mas->min, otherwise we need to walk up
to find the implied pivot min.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
 include/linux/maple_tree.h | 4 ++--
 lib/maple_tree.c           | 9 +++++++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 9ef129038224..bafe143b1f78 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -75,8 +75,8 @@
  * searching for gaps or any other code that needs to find the end of the data.
  */
 struct maple_metadata {
-	unsigned char end;
-	unsigned char gap;
+	unsigned char end;	/* end of data */
+	unsigned char gap;	/* offset of largest gap */
 };
 
 /*
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 6c89e6790fb5..e4735ccd06f2 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -338,7 +338,7 @@ static inline void mte_set_node_dead(struct maple_enode *mn)
 	smp_wmb(); /* Needed for RCU */
 }
 
-/* Bit 1 indicates the root is a node */
+/* Bit 1 indicates the node is the root */
 #define MAPLE_ROOT_NODE			0x02
 /* maple_type stored bit 3-6 */
 #define MAPLE_ENODE_TYPE_SHIFT		0x03
@@ -1053,7 +1053,7 @@ static inline void mte_set_gap(const struct maple_enode *mn,
  * mas_ascend() - Walk up a level of the tree.
  * @mas: The maple state
  *
- * Sets the @mas->max and @mas->min to the correct values when walking up.  This
+ * Sets the @mas->max and @mas->min for the parent node of mas->node.  This
  * may cause several levels of walking up to find the correct min and max.
  * May find a dead node which will cause a premature return.
  * Return: 1 on dead node, 0 otherwise
@@ -1098,6 +1098,11 @@ static int mas_ascend(struct ma_state *mas)
 
 	min = 0;
 	max = ULONG_MAX;
+
+	/*
+	 * !mas->offset => parent node min == mas->min. mas->offset => need
+	 * to walk up to find the implied pivot min.
+	 */
 	if (!mas->offset) {
 		min = mas->min;
 		set_min = true;
-- 
2.30.2