patches/old/maple-tree-add-some-comments.patch

From: Dev Jain <dev.jain@arm.com>
Subject: maple tree: add some comments
Date: Thu, 3 Jul 2025 12:03:38 +0530

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.

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.

Link: https://lkml.kernel.org/r/20250703063338.51509-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/maple_tree.h |    4 ++--
 lib/maple_tree.c           |    8 +++++++-
 2 files changed, 9 insertions(+), 3 deletions(-)

--- a/include/linux/maple_tree.h~maple-tree-add-some-comments
+++ a/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 */
 };
 
 /*
--- a/lib/maple_tree.c~maple-tree-add-some-comments
+++ a/lib/maple_tree.c
@@ -1053,7 +1053,7 @@ static inline void mte_set_gap(const str
  * 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 +1098,12 @@ static int mas_ascend(struct ma_state *m
 
 	min = 0;
 	max = ULONG_MAX;
+
+	/*
+	 * !mas->offset implies that parent node min == mas->min.
+	 * mas->offset > 0 implies that we need to walk up to find the
+	 * implied pivot min.
+	 */
 	if (!mas->offset) {
 		min = mas->min;
 		set_min = true;
_