maple_tree: try harder to keep active node after mas_next()

Clean up the mas_next() call to try and keep a node reference when
possible.  This will avoid re-walking the tree in most cases.

Also clean up the single entry tree handling to ensure index/last are
consistent with what one would expect.  (returning NULL with limit of
1-oo).

Link: https://lkml.kernel.org/r/20230518145544.1722059-24-Liam.Howlett@oracle.com
Signed-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

@@ -4727,33 +4727,25 @@ static inline void *mas_next_nentry(struct ma_state *mas,
 		if (ma_dead_node(node))
 			return NULL;
 
+		mas->last = pivot;
 		if (entry)
-			goto found;
+			return entry;
 
 		if (pivot >= max)
 			return NULL;
 
+		if (pivot >= mas->max)
+			return NULL;
+
 		mas->index = pivot + 1;
 		mas->offset++;
 	}
 
-	if (mas->index > mas->max) {
+	pivot = mas_logical_pivot(mas, pivots, mas->offset, type);
-		mas->index = mas->last;
-		return NULL;
-	}
-
-	pivot = mas_safe_pivot(mas, pivots, mas->offset, type);
 	entry = mas_slot(mas, slots, mas->offset);
 	if (ma_dead_node(node))
 		return NULL;
 
-	if (!pivot)
-		return NULL;
-
-	if (!entry)
-		return NULL;
-
-found:
 	mas->last = pivot;
 	return entry;
 }
@@ -4782,21 +4774,15 @@ retry:
 static inline void *mas_next_entry(struct ma_state *mas, unsigned long limit)
 {
 	void *entry = NULL;
-	struct maple_enode *prev_node;
 	struct maple_node *node;
-	unsigned char offset;
 	unsigned long last;
 	enum maple_type mt;
 
-	if (mas->index > limit) {
+	if (mas->last >= limit)
-		mas->index = mas->last = limit;
-		mas_pause(mas);
 		return NULL;
-	}
+
 	last = mas->last;
 retry:
-	offset = mas->offset;
-	prev_node = mas->node;
 	node = mas_mn(mas);
 	mt = mte_node_type(mas->node);
 	mas->offset++;
@@ -4815,12 +4801,10 @@ retry:
 		if (likely(entry))
 			return entry;
 
-		if (unlikely((mas->index > limit)))
+		if (unlikely((mas->last >= limit)))
-			break;
+			return NULL;
 
 next_node:
-		prev_node = mas->node;
-		offset = mas->offset;
 		if (unlikely(mas_next_node(mas, node, limit))) {
 			mas_rewalk(mas, last);
 			goto retry;
@@ -4830,9 +4814,6 @@ next_node:
 		mt = mte_node_type(mas->node);
 	}
 
-	mas->index = mas->last = limit;
-	mas->offset = offset;
-	mas->node = prev_node;
 	return NULL;
 }
 
@@ -5914,6 +5895,8 @@ EXPORT_SYMBOL_GPL(mas_expected_entries);
  */
 void *mas_next(struct ma_state *mas, unsigned long max)
 {
+	bool was_none = mas_is_none(mas);
+
 	if (mas_is_none(mas) || mas_is_paused(mas))
 		mas->node = MAS_START;
 
@@ -5921,16 +5904,16 @@ void *mas_next(struct ma_state *mas, unsigned long max)
 		mas_walk(mas); /* Retries on dead nodes handled by mas_walk */
 
 	if (mas_is_ptr(mas)) {
-		if (!mas->index) {
+		if (was_none && mas->index == 0) {
-			mas->index = 1;
+			mas->index = mas->last = 0;
-			mas->last = ULONG_MAX;
+			return mas_root(mas);
 		}
+		mas->index = 1;
+		mas->last = ULONG_MAX;
+		mas->node = MAS_NONE;
 		return NULL;
 	}
 
-	if (mas->last == ULONG_MAX)
-		return NULL;
-
 	/* Retries on dead nodes handled by mas_next_entry */
 	return mas_next_entry(mas, max);
 }
@@ -6054,17 +6037,25 @@ EXPORT_SYMBOL_GPL(mas_pause);
  */
 void *mas_find(struct ma_state *mas, unsigned long max)
 {
-	if (unlikely(mas_is_paused(mas))) {
+	if (unlikely(mas_is_none(mas))) {
-		if (unlikely(mas->last == ULONG_MAX)) {
+		if (unlikely(mas->last >= max))
-			mas->node = MAS_NONE;
 			return NULL;
-		}
+
+		mas->index = mas->last;
+		mas->node = MAS_START;
+	}
+
+	if (unlikely(mas_is_paused(mas))) {
+		if (unlikely(mas->last >= max))
+			return NULL;
+
 		mas->node = MAS_START;
 		mas->index = ++mas->last;
 	}
 
-	if (unlikely(mas_is_none(mas)))
+
-		mas->node = MAS_START;
+	if (unlikely(mas_is_ptr(mas)))
+		goto ptr_out_of_range;
 
 	if (unlikely(mas_is_start(mas))) {
 		/* First run or continue */
@@ -6076,13 +6067,27 @@ void *mas_find(struct ma_state *mas, unsigned long max)
 		entry = mas_walk(mas);
 		if (entry)
 			return entry;
+
 	}
 
-	if (unlikely(!mas_searchable(mas)))
+	if (unlikely(!mas_searchable(mas))) {
+		if (unlikely(mas_is_ptr(mas)))
+			goto ptr_out_of_range;
+
+		return NULL;
+	}
+
+	if (mas->index == max)
 		return NULL;
 
 	/* Retries on dead nodes handled by mas_next_entry */
 	return mas_next_entry(mas, max);
+
+ptr_out_of_range:
+	mas->node = MAS_NONE;
+	mas->index = 1;
+	mas->last = ULONG_MAX;
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(mas_find);
 
@@ -6513,7 +6518,7 @@ retry:
 	if (entry)
 		goto unlock;
 
-	while (mas_searchable(&mas) && (mas.index < max)) {
+	while (mas_searchable(&mas) && (mas.last < max)) {
 		entry = mas_next_entry(&mas, max);
 		if (likely(entry && !xa_is_zero(entry)))
 			break;