linux-kernel - [PATCH 11/12] maple_tree: Add single node allocation support to maple state

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Message-Id: <20250901-maple-sheaves-v1-11-d6a1166b53f2@suse.cz>
Date: Mon, 01 Sep 2025 13:09:01 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Matthew Wilcox <willy@...radead.org>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Jann Horn <jannh@...gle.com>, 
 Pedro Falcato <pfalcato@...e.de>, Suren Baghdasaryan <surenb@...gle.com>
Cc: Harry Yoo <harry.yoo@...cle.com>, 
 Andrew Morton <akpm@...ux-foundation.org>, maple-tree@...ts.infradead.org, 
 linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH 11/12] maple_tree: Add single node allocation support to
 maple state

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

The fast path through a write will require replacing a single node in
the tree.  Using a sheaf (32 nodes) is too heavy for the fast path, so
special case the node store operation by just allocating one node in the
maple state.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 include/linux/maple_tree.h       |  4 +++-
 lib/maple_tree.c                 | 47 +++++++++++++++++++++++++++++++++++-----
 tools/testing/radix-tree/maple.c |  9 ++++++--
 3 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index 166fd67e00d882b1e6de1f80c1b590bba7497cd3..562a1e9e5132b5b1fa8f8402a7cadd8abb65e323 100644
--- a/include/linux/maple_tree.h
+++ b/include/linux/maple_tree.h
@@ -443,6 +443,7 @@ struct ma_state {
 	unsigned long min;		/* The minimum index of this node - implied pivot min */
 	unsigned long max;		/* The maximum index of this node - implied pivot max */
 	struct slab_sheaf *sheaf;	/* Allocated nodes for this operation */
+	struct maple_node *alloc;	/* allocated nodes */
 	unsigned long node_request;
 	enum maple_status status;	/* The status of the state (active, start, none, etc) */
 	unsigned char depth;		/* depth of tree descent during write */
@@ -491,8 +492,9 @@ struct ma_wr_state {
 		.status = ma_start,					\
 		.min = 0,						\
 		.max = ULONG_MAX,					\
-		.node_request= 0,					\
 		.sheaf = NULL,						\
+		.alloc = NULL,						\
+		.node_request= 0,					\
 		.mas_flags = 0,						\
 		.store_type = wr_invalid,				\
 	}
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index cfe80c50a97e3118eefc24275fbcd2eec5e6e6e8..61a322f945c28f5c3297c506923f00bcce5c7bca 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1095,16 +1095,23 @@ static int mas_ascend(struct ma_state *mas)
  *
  * Return: A pointer to a maple node.
  */
-static inline struct maple_node *mas_pop_node(struct ma_state *mas)
+static __always_inline struct maple_node *mas_pop_node(struct ma_state *mas)
 {
 	struct maple_node *ret;
 
+	if (mas->alloc) {
+		ret = mas->alloc;
+		mas->alloc = NULL;
+		goto out;
+	}
+
 	if (WARN_ON_ONCE(!mas->sheaf))
 		return NULL;
 
 	ret = kmem_cache_alloc_from_sheaf(maple_node_cache, GFP_NOWAIT, mas->sheaf);
-	memset(ret, 0, sizeof(*ret));
 
+out:
+	memset(ret, 0, sizeof(*ret));
 	return ret;
 }
 
@@ -1115,9 +1122,34 @@ static inline struct maple_node *mas_pop_node(struct ma_state *mas)
  */
 static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
 {
-	if (unlikely(mas->sheaf)) {
-		unsigned long refill = mas->node_request;
+	if (!mas->node_request)
+		return;
+
+	if (mas->node_request == 1) {
+		if (mas->sheaf)
+			goto use_sheaf;
+
+		if (mas->alloc)
+			return;
 
+		mas->alloc = mt_alloc_one(gfp);
+		if (!mas->alloc)
+			goto error;
+
+		mas->node_request = 0;
+		return;
+	}
+
+use_sheaf:
+	if (unlikely(mas->alloc)) {
+		kfree(mas->alloc);
+		mas->alloc = NULL;
+	}
+
+	if (mas->sheaf) {
+		unsigned long refill;
+
+		refill = mas->node_request;
 		if(kmem_cache_sheaf_size(mas->sheaf) >= refill) {
 			mas->node_request = 0;
 			return;
@@ -5380,8 +5412,11 @@ void mas_destroy(struct ma_state *mas)
 	mas->node_request = 0;
 	if (mas->sheaf)
 		mt_return_sheaf(mas->sheaf);
-
 	mas->sheaf = NULL;
+
+	if (mas->alloc)
+		kfree(mas->alloc);
+	mas->alloc = NULL;
 }
 EXPORT_SYMBOL_GPL(mas_destroy);
 
@@ -6079,7 +6114,7 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
 		mas_alloc_nodes(mas, gfp);
 	}
 
-	if (!mas->sheaf)
+	if (!mas->sheaf && !mas->alloc)
 		return false;
 
 	mas->status = ma_start;
diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index da3e03d73b52162dab6fa5c368ad7b71b9e58521..89da991e12cd97e44971757ddc105ef46c68ea4c 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -35095,10 +35095,15 @@ static unsigned char get_vacant_height(struct ma_wr_state *wr_mas, void *entry)
 
 static int mas_allocated(struct ma_state *mas)
 {
+	int total = 0;
+
+	if (mas->alloc)
+		total++;
+
 	if (mas->sheaf)
-		return kmem_cache_sheaf_size(mas->sheaf);
+		total += kmem_cache_sheaf_size(mas->sheaf);
 
-	return 0;
+	return total;
 }
 /* Preallocation testing */
 static noinline void __init check_prealloc(struct maple_tree *mt)

-- 
2.51.0