linux-kernel - [PATCH 6.6.y] maple_tree: do not preallocate nodes for slot stores

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Message-ID: <20231212195255.219624-1-sidhartha.kumar@oracle.com>
Date:   Tue, 12 Dec 2023 11:52:55 -0800
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        maple-tree@...ts.infradead.org
Cc:     akpm@...ux-foundation.org, willy@...radead.org,
        liam.howlett@...cle.com, zhangpeng.00@...edance.com,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        stable@...r.kernel.org
Subject: [PATCH 6.6.y] maple_tree: do not preallocate nodes for slot stores

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.

Fixes: 0b8bb544b1a7 ("maple_tree: update mas_preallocate() testing")
Cc: <stable@...r.kernel.org> # 6.6+
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
---
This is a modified backport as the patch to fix this in upstream does not
apply to 6.6 because the node_end field was moved from the ma_wr_state to
the ma_state after 6.6.

 lib/maple_tree.c                 | 6 ++++++
 tools/testing/radix-tree/maple.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index bb24d84a4922f..5950d0c0e0f69 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5501,6 +5501,12 @@ int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
 
 	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) && ((!mt_in_rcu(mas->tree))
+		|| (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;
diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index e5da1cad70baf..76a8990bb14e8 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -35538,7 +35538,7 @@ static noinline void __init check_prealloc(struct maple_tree *mt)
 	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);
 
-- 
2.42.0