maple_tree: Add single node allocation support to maple state

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 <[email protected]>
Signed-off-by: Vlastimil Babka <[email protected]>

Author: howlett

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;	/* A single allocated node for fast path writes */
 	unsigned long node_request;	/* The number of nodes to allocate for this operation */
 	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,				\
 	}

lib/maple_tree.c

@@ -1073,16 +1073,23 @@ 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;
 }
 
@@ -1093,9 +1100,34 @@ 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;
@@ -5180,8 +5212,11 @@ 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);
 
@@ -5816,7 +5851,7 @@ 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;

tools/testing/radix-tree/maple.c

@@ -35085,10 +35085,15 @@ 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)