+ maple_tree-refine-mas_store_root-on-storing-null.patch added to mm-unstable branch

+ maple_tree-refine-mas_store_root-on-storing-null.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: maple_tree: refine mas_store_root() on storing NULL
has been added to the -mm mm-unstable branch.  Its filename is
     maple_tree-refine-mas_store_root-on-storing-null.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-refine-mas_store_root-on-storing-null.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Wei Yang <richard.weiyang@gmail.com>
Subject: maple_tree: refine mas_store_root() on storing NULL
Date: Thu, 31 Oct 2024 23:16:26 +0000

Currently, when storing NULL on mas_store_root(), 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
  * it allows for multiple NULL entries by expanding root
    to store NULLs to an empty tree

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

Link: https://lkml.kernel.org/r/20241031231627.14316-5-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/lib/maple_tree.c~maple_tree-refine-mas_store_root-on-storing-null
+++ a/lib/maple_tree.c
@@ -3447,9 +3447,20 @@ static inline void mas_root_expand(struc
 	return;
 }
 
+/*
+ * mas_store_root() - Storing value into root.
+ * @mas: The maple state
+ * @entry: The entry to store.
+ *
+ * There is no root node now and we are storing a value into the root - this
+ * function either assigns the pointer or expands into a node.
+ */
 static inline void mas_store_root(struct ma_state *mas, void *entry)
 {
-	if (likely((mas->last != 0) || (mas->index != 0)))
+	if (!entry) {
+		if (!mas->index)
+			rcu_assign_pointer(mas->tree->ma_root, NULL);
+	} else if (likely((mas->last != 0) || (mas->index != 0)))
 		mas_root_expand(mas, entry);
 	else if (((unsigned long) (entry) & 3) == 2)
 		mas_root_expand(mas, entry);
_

Patches currently in -mm which might be from richard.weiyang@gmail.com are

mm-mlock-set-the-correct-prev-on-failure.patch
maple_tree-i-is-always-less-than-or-equal-to-mas_end.patch
maple_tree-goto-complete-directly-on-a-pivot-of-0.patch
maple_tree-remove-maple_big_nodeparent.patch
maple_tree-memset-maple_big_node-as-a-whole.patch
maple_tree-root-node-could-be-handled-by-p_slot-too.patch
maple_tree-clear-request_count-for-new-allocated-one.patch
maple_tree-total-is-not-changed-for-nomem_one-case.patch
maple_tree-simplify-mas_push_node.patch
maple_tree-calculate-new_end-when-needed.patch
maple_tree-remove-sanity-check-from-mas_wr_slot_store.patch
mm-vma-the-pgoff-is-correct-if-can_merge_right.patch
maple_tree-print-empty-for-an-empty-tree-on-mt_dump.patch
maple_tree-the-return-value-of-mas_root_expand-is-not-used.patch
maple_tree-not-necessary-to-check-index-last-again.patch
maple_tree-refine-mas_store_root-on-storing-null.patch
maple_tree-add-a-test-checking-storing-null.patch