Currently, when storing NULL on mas_root_expand(), the behavior could be
improved.
For example possible cases are:
* store NULL at any range result a new node
* store NULL at range [m, n] where m > 0 to a single entry tree result
a new node with range [m, n] set to NULL
* store NULL at range [m, n] where m > 0 to an empty tree result
consecutive NULL slot
This patch tries to improve in:
* memory efficient by setting to empty tree instead of using a node
* remove the possibility of consecutive NULL slot which will prohibit
extended null in later operation
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
CC: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
CC: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
CC: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
lib/maple_tree.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index a90c29156fe2..15d2124acc36 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3335,6 +3335,24 @@ static inline void mas_root_expand(struct ma_state *mas, void *entry)
unsigned long *pivots;
int slot = 0;
+ if (!entry) {
+ /*
+ * We come here in two cases:
+ * 1. This is an empty tree
+ * 2. This is a single entry tree with range [0, 0]
+ *
+ * If this is an empty tree, the result should still be an
+ * empty tree no matter what the range is.
+ *
+ * If this is a single entry tree, we should set it to an
+ * empty tree if the range cover [0, 0]. Otherwise, we don't
+ * need to change it.
+ */
+ if (!mas->index && contents)
+ rcu_assign_pointer(mas->tree->ma_root, NULL);
+ return;
+ }
+
node = mas_pop_node(mas);
pivots = ma_pivots(node, type);
slots = ma_slots(node, type);
--
2.34.1
