+ maple_tree-do-not-preallocate-nodes-for-slot-stores.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: maple_tree: do not preallocate nodes for slot stores
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     maple_tree-do-not-preallocate-nodes-for-slot-stores.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-do-not-preallocate-nodes-for-slot-stores.patch

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

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------------------------------------------------------
From: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Subject: maple_tree: do not preallocate nodes for slot stores
Date: Wed, 13 Dec 2023 12:50:57 -0800

mas_preallocate() defaults to requesting 1 node for preallocation and then
,depending on the type of store, will update the request variable.  There
isn't a check for a slot store type, so slot stores are preallocating the
default 1 node.  Slot stores do not require any additional nodes, so add a
check for the slot store case that will bypass node_count_gfp().  Update
the tests to reflect that slot stores do not require allocations.

User visible effects of this bug include increased memory usage from the
unneeded node that was allocated.

Link: https://lkml.kernel.org/r/20231213205058.386589-1-sidhartha.kumar@oracle.com
Fixes: 0b8bb544b1a7 ("maple_tree: update mas_preallocate() testing")
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: <stable@vger.kernel.org>	[6.6+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c                 |   11 +++++++++++
 tools/testing/radix-tree/maple.c |    2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

--- a/lib/maple_tree.c~maple_tree-do-not-preallocate-nodes-for-slot-stores
+++ a/lib/maple_tree.c
@@ -5501,6 +5501,17 @@ int mas_preallocate(struct ma_state *mas
 
 	mas_wr_end_piv(&wr_mas);
 	node_size = mas_wr_new_end(&wr_mas);
+
+	/* Slot store, does not require additional nodes */
+	if (node_size == wr_mas.node_end) {
+		/* reuse node */
+		if (!mt_in_rcu(mas->tree))
+			return 0;
+		/* shifting boundary */
+		if (wr_mas.offset_end - mas->offset == 1)
+			return 0;
+	}
+
 	if (node_size >= mt_slots[wr_mas.type]) {
 		/* Split, worst case for now. */
 		request = 1 + mas_mt_height(mas) * 2;
--- a/tools/testing/radix-tree/maple.c~maple_tree-do-not-preallocate-nodes-for-slot-stores
+++ a/tools/testing/radix-tree/maple.c
@@ -35538,7 +35538,7 @@ static noinline void __init check_preall
 	MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0);
 	allocated = mas_allocated(&mas);
 	height = mas_mt_height(&mas);
-	MT_BUG_ON(mt, allocated != 1);
+	MT_BUG_ON(mt, allocated != 0);
 	mas_store_prealloc(&mas, ptr);
 	MT_BUG_ON(mt, mas_allocated(&mas) != 0);
 
_

Patches currently in -mm which might be from sidhartha.kumar@oracle.com are

maple_tree-do-not-preallocate-nodes-for-slot-stores.patch