+ maple_tree-memset-maple_big_node-as-a-whole.patch added to mm-unstable branch

+ maple_tree-memset-maple_big_node-as-a-whole.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: maple_tree: memset maple_big_node as a whole
has been added to the -mm mm-unstable branch.  Its filename is
     maple_tree-memset-maple_big_node-as-a-whole.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-memset-maple_big_node-as-a-whole.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: memset maple_big_node as a whole
Date: Sun, 8 Sep 2024 14:05:54 +0000

In mast_fill_bnode(), we first clear some fields of maple_big_node and set
the 'type' unconditionally before return.  This means we won't leverage
any information in maple_big_node and it is safe to clear the whole
structure.

In maple_big_node, we define slot and padding/gap in a union.  And based
on current definition of MAPLE_BIG_NODE_SLOTS/GAPS, padding is always less
than slot and part of the gap is overlapped by slot.

For example on 64bit system:

  MAPLE_BIG_NODE_SLOT is 34
  MAPLE_BIG_NODE_GAP  is 21

With this knowledge, current code may clear some space by twice. And
this could be avoid by clearing the structure as a whole.

Link: https://lkml.kernel.org/r/20240908140554.20378-3-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/lib/maple_tree.c~maple_tree-memset-maple_big_node-as-a-whole
+++ a/lib/maple_tree.c
@@ -3155,10 +3155,7 @@ static inline void mast_fill_bnode(struc
 	bool cp = true;
 	unsigned char split;
 
-	memset(mast->bn->gap, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->gap));
-	memset(mast->bn->slot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->slot));
-	memset(mast->bn->pivot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->pivot));
-	mast->bn->b_end = 0;
+	memset(mast->bn, 0, sizeof(struct maple_big_node));
 
 	if (mte_is_root(mas->node)) {
 		cp = false;
_

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

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