maple_tree: introduce mas_next_slot() interface

Sometimes, during a tree walk, the user needs the next slot regardless of
if it is empty or not.  Add an interface to get the next slot.

Since there are no consecutive NULLs allowed in the tree, the mas_next()
function can only advance two slots at most.  So use the new
mas_next_slot() interface to align both implementations.  Use this method
for mas_find() as well.

Link: https://lkml.kernel.org/r/20230518145544.1722059-28-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -4607,11 +4607,10 @@ static inline int mas_prev_node(struct ma_state *mas, unsigned long min)
 static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 				unsigned long max)
 {
-	unsigned long min, pivot;
+	unsigned long min;
 	unsigned long *pivots;
 	struct maple_enode *enode;
 	int level = 0;
-	unsigned char offset;
 	unsigned char node_end;
 	enum maple_type mt;
 	void __rcu **slots;
@@ -4619,19 +4618,16 @@ static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 	if (mas->max >= max)
 		goto no_entry;
 
+	min = mas->max + 1;
 	level = 0;
 	do {
 		if (ma_is_root(node))
 			goto no_entry;
 
-		min = mas->max + 1;
-		if (min > max)
-			goto no_entry;
-
+		/* Walk up. */
 		if (unlikely(mas_ascend(mas)))
 			return 1;
 
-		offset = mas->offset;
 		level++;
 		node = mas_mn(mas);
 		mt = mte_node_type(mas->node);
@@ -4640,36 +4636,37 @@ static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 		if (unlikely(ma_dead_node(node)))
 			return 1;
 
-	} while (unlikely(offset == node_end));
+	} while (unlikely(mas->offset == node_end));
 
 	slots = ma_slots(node, mt);
-	pivot = mas_safe_pivot(mas, pivots, ++offset, mt);
-	while (unlikely(level > 1)) {
-		/* Descend, if necessary */
-		enode = mas_slot(mas, slots, offset);
+	mas->offset++;
+	enode = mas_slot(mas, slots, mas->offset);
 	if (unlikely(ma_dead_node(node)))
 		return 1;
 
-		mas->node = enode;
+	if (level > 1)
+		mas->offset = 0;
+
+	while (unlikely(level > 1)) {
 		level--;
+		mas->node = enode;
 		node = mas_mn(mas);
 		mt = mte_node_type(mas->node);
 		slots = ma_slots(node, mt);
-		pivots = ma_pivots(node, mt);
+		enode = mas_slot(mas, slots, 0);
 		if (unlikely(ma_dead_node(node)))
 			return 1;
-
-		offset = 0;
-		pivot = pivots[0];
 	}
 
-	enode = mas_slot(mas, slots, offset);
+	if (!mas->offset)
+		pivots = ma_pivots(node, mt);
+
+	mas->max = mas_safe_pivot(mas, pivots, mas->offset, mt);
 	if (unlikely(ma_dead_node(node)))
 		return 1;
 
 	mas->node = enode;
 	mas->min = min;
-	mas->max = pivot;
 	return 0;
 
 no_entry:
@@ -4680,83 +4677,106 @@ static inline int mas_next_node(struct ma_state *mas, struct maple_node *node,
 	return 0;
 }
 
+static inline void mas_rewalk(struct ma_state *mas, unsigned long index)
+{
+retry:
+	mas_set(mas, index);
+	mas_state_walk(mas);
+	if (mas_is_start(mas))
+		goto retry;
+}
+
+static inline bool mas_rewalk_if_dead(struct ma_state *mas,
+		struct maple_node *node, const unsigned long index)
+{
+	if (unlikely(ma_dead_node(node))) {
+		mas_rewalk(mas, index);
+		return true;
+	}
+	return false;
+}
+
 /*
- * mas_next_nentry() - Get the next node entry
- * @mas: The maple state
- * @max: The maximum value to check
- * @*range_start: Pointer to store the start of the range.
+ * mas_next_slot() - Get the entry in the next slot
  *
- * Sets @mas->offset to the offset of the next node entry, @mas->last to the
- * pivot of the entry.
+ * @mas: The maple state
+ * @max: The maximum starting range
+ * @empty: Can be empty
  *
- * Return: The next entry, %NULL otherwise
+ * Return: The entry in the next slot which is possibly NULL
  */
-static inline void *mas_next_nentry(struct ma_state *mas,
-	    struct maple_node *node, unsigned long max, enum maple_type type)
+static void *mas_next_slot(struct ma_state *mas, unsigned long max, bool empty)
 {
-	unsigned char count;
-	unsigned long pivot;
-	unsigned long *pivots;
 	void __rcu **slots;
+	unsigned long *pivots;
+	unsigned long pivot;
+	enum maple_type type;
+	struct maple_node *node;
+	unsigned char data_end;
+	unsigned long save_point = mas->last;
 	void *entry;
 
-	if (mas->last == mas->max) {
-		mas->index = mas->max;
-		return NULL;
-	}
-
-	slots = ma_slots(node, type);
+retry:
+	node = mas_mn(mas);
+	type = mte_node_type(mas->node);
 	pivots = ma_pivots(node, type);
-	count = ma_data_end(node, type, pivots, mas->max);
-	if (unlikely(ma_dead_node(node)))
-		return NULL;
-
-	mas->index = mas_safe_min(mas, pivots, mas->offset);
-	if (unlikely(ma_dead_node(node)))
-		return NULL;
-
-	if (mas->index > max)
-		return NULL;
-
-	if (mas->offset > count)
-		return NULL;
+	data_end = ma_data_end(node, type, pivots, mas->max);
+	if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
+		goto retry;
 
-	while (mas->offset < count) {
+again:
+	if (mas->max >= max) {
+		if (likely(mas->offset < data_end))
 			pivot = pivots[mas->offset];
-		entry = mas_slot(mas, slots, mas->offset);
-		if (ma_dead_node(node))
-			return NULL;
+		else
+			return NULL; /* must be mas->max */
 
-		mas->last = pivot;
-		if (entry)
-			return entry;
+		if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
+			goto retry;
 
 		if (pivot >= max)
 			return NULL;
+	}
 
-		if (pivot >= mas->max)
-			return NULL;
-
-		mas->index = pivot + 1;
+	if (likely(mas->offset < data_end)) {
+		mas->index = pivots[mas->offset] + 1;
 		mas->offset++;
+		if (likely(mas->offset < data_end))
+			mas->last = pivots[mas->offset];
+		else
+			mas->last = mas->max;
+	} else  {
+		if (mas_next_node(mas, node, max)) {
+			mas_rewalk(mas, save_point);
+			goto retry;
 		}
 
-	pivot = mas_logical_pivot(mas, pivots, mas->offset, type);
-	entry = mas_slot(mas, slots, mas->offset);
-	if (ma_dead_node(node))
+		if (mas_is_none(mas))
 			return NULL;
 
-	mas->last = pivot;
-	return entry;
-}
+		mas->offset = 0;
+		mas->index = mas->min;
+		node = mas_mn(mas);
+		type = mte_node_type(mas->node);
+		pivots = ma_pivots(node, type);
+		mas->last = pivots[0];
+	}
 
-static inline void mas_rewalk(struct ma_state *mas, unsigned long index)
-{
-retry:
-	mas_set(mas, index);
-	mas_state_walk(mas);
-	if (mas_is_start(mas))
+	slots = ma_slots(node, type);
+	entry = mt_slot(mas->tree, slots, mas->offset);
+	if (unlikely(mas_rewalk_if_dead(mas, node, save_point)))
 		goto retry;
+
+	if (entry)
+		return entry;
+
+	if (!empty) {
+		if (!mas->offset)
+			data_end = 2;
+		goto again;
+	}
+
+	return entry;
 }
 
 /*
@@ -4774,47 +4794,12 @@ static inline void mas_rewalk(struct ma_state *mas, unsigned long index)
 static inline void *mas_next_entry(struct ma_state *mas, unsigned long limit)
 {
 	void *entry = NULL;
-	struct maple_node *node;
-	unsigned long last;
-	enum maple_type mt;
 
 	if (mas->last >= limit)
 		return NULL;
 
-	last = mas->last;
-retry:
-	node = mas_mn(mas);
-	mt = mte_node_type(mas->node);
-	mas->offset++;
-	if (unlikely(mas->offset >= mt_slots[mt])) {
-		mas->offset = mt_slots[mt] - 1;
-		goto next_node;
-	}
-
-	while (!mas_is_none(mas)) {
-		entry = mas_next_nentry(mas, node, limit, mt);
-		if (unlikely(ma_dead_node(node))) {
-			mas_rewalk(mas, last);
-			goto retry;
-		}
-
-		if (likely(entry))
+	entry = mas_next_slot(mas, limit, false);
 	return entry;
-
-		if (unlikely((mas->last >= limit)))
-			return NULL;
-
-next_node:
-		if (unlikely(mas_next_node(mas, node, limit))) {
-			mas_rewalk(mas, last);
-			goto retry;
-		}
-		mas->offset = 0;
-		node = mas_mn(mas);
-		mt = mte_node_type(mas->node);
-	}
-
-	return NULL;
 }
 
 /*
@@ -4845,10 +4830,8 @@ static inline void *mas_prev_nentry(struct ma_state *mas, unsigned long limit,
 	slots = ma_slots(mn, mt);
 	pivots = ma_pivots(mn, mt);
 	count = ma_data_end(mn, mt, pivots, mas->max);
-	if (unlikely(ma_dead_node(mn))) {
-		mas_rewalk(mas, index);
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
 		goto retry;
-	}
 
 	offset = mas->offset - 1;
 	if (offset >= mt_slots[mt])
@@ -4861,10 +4844,8 @@ static inline void *mas_prev_nentry(struct ma_state *mas, unsigned long limit,
 		pivot = pivots[offset];
 	}
 
-	if (unlikely(ma_dead_node(mn))) {
-		mas_rewalk(mas, index);
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
 		goto retry;
-	}
 
 	while (offset && !mas_slot(mas, slots, offset)) {
 		pivot = pivots[--offset];
@@ -4881,10 +4862,8 @@ static inline void *mas_prev_nentry(struct ma_state *mas, unsigned long limit,
 
 	min = mas_safe_min(mas, pivots, offset);
 	entry = mas_slot(mas, slots, offset);
-	if (unlikely(ma_dead_node(mn))) {
-		mas_rewalk(mas, index);
+	if (unlikely(mas_rewalk_if_dead(mas, mn, index)))
 		goto retry;
-	}
 
 	mas->offset = offset;
 	mas->last = pivot;
@@ -6103,8 +6082,8 @@ void *mas_find(struct ma_state *mas, unsigned long max)
 	if (mas->index == max)
 		return NULL;
 
-	/* Retries on dead nodes handled by mas_next_entry */
-	return mas_next_entry(mas, max);
+	/* Retries on dead nodes handled by mas_next_slot */
+	return mas_next_slot(mas, max, false);
 
 ptr_out_of_range:
 	mas->node = MAS_NONE;