lib/generic-radix-tree.c: Make nodes more reasonably sized

this code originally used the page allocator directly, but most code
shouldn't do that - PAGE_SIZE varies with architecture, and slab is
faster.

4k is also on the large side for typical usage, 512 bytes is a better
choice for typical usage that might be somewhat sparse.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

include/linux/generic-radix-tree.h

@@ -5,7 +5,7 @@
  * DOC: Generic radix trees/sparse arrays
  *
  * Very simple and minimalistic, supporting arbitrary size entries up to
- * PAGE_SIZE.
+ * GENRADIX_NODE_SIZE.
  *
  * A genradix is defined with the type it will store, like so:
  *
@@ -45,12 +45,15 @@
 
 struct genradix_root;
 
+#define GENRADIX_NODE_SHIFT	9
+#define GENRADIX_NODE_SIZE	(1U << GENRADIX_NODE_SHIFT)
+
 struct __genradix {
 	struct genradix_root		*root;
 };
 
 /*
- * NOTE: currently, sizeof(_type) must not be larger than PAGE_SIZE:
+ * NOTE: currently, sizeof(_type) must not be larger than GENRADIX_NODE_SIZE:
  */
 
 #define __GENRADIX_INITIALIZER					\
@@ -101,14 +104,14 @@ void __genradix_free(struct __genradix *);
 static inline size_t __idx_to_offset(size_t idx, size_t obj_size)
 {
 	if (__builtin_constant_p(obj_size))
-		BUILD_BUG_ON(obj_size > PAGE_SIZE);
+		BUILD_BUG_ON(obj_size > GENRADIX_NODE_SIZE);
 	else
-		BUG_ON(obj_size > PAGE_SIZE);
+		BUG_ON(obj_size > GENRADIX_NODE_SIZE);
 
 	if (!is_power_of_2(obj_size)) {
-		size_t objs_per_page = PAGE_SIZE / obj_size;
+		size_t objs_per_page = GENRADIX_NODE_SIZE / obj_size;
 
-		return (idx / objs_per_page) * PAGE_SIZE +
+		return (idx / objs_per_page) * GENRADIX_NODE_SIZE +
 			(idx % objs_per_page) * obj_size;
 	} else {
 		return idx * obj_size;
@@ -118,9 +121,9 @@ static inline size_t __idx_to_offset(size_t idx, size_t obj_size)
 #define __genradix_cast(_radix)		(typeof((_radix)->type[0]) *)
 #define __genradix_obj_size(_radix)	sizeof((_radix)->type[0])
 #define __genradix_objs_per_page(_radix)			\
-	(PAGE_SIZE / sizeof((_radix)->type[0]))
+	(GENRADIX_NODE_SIZE / sizeof((_radix)->type[0]))
 #define __genradix_page_remainder(_radix)			\
-	(PAGE_SIZE % sizeof((_radix)->type[0]))
+	(GENRADIX_NODE_SIZE % sizeof((_radix)->type[0]))
 
 #define __genradix_idx_to_offset(_radix, _idx)			\
 	__idx_to_offset(_idx, __genradix_obj_size(_radix))
@@ -217,8 +220,8 @@ static inline void __genradix_iter_advance(struct genradix_iter *iter,
 	iter->offset += obj_size;
 
 	if (!is_power_of_2(obj_size) &&
-	    (iter->offset & (PAGE_SIZE - 1)) + obj_size > PAGE_SIZE)
-		iter->offset = round_up(iter->offset, PAGE_SIZE);
+	    (iter->offset & (GENRADIX_NODE_SIZE - 1)) + obj_size > GENRADIX_NODE_SIZE)
+		iter->offset = round_up(iter->offset, GENRADIX_NODE_SIZE);
 
 	iter->pos++;
 }
@@ -235,8 +238,8 @@ static inline void __genradix_iter_rewind(struct genradix_iter *iter,
 		return;
 	}
 
-	if ((iter->offset & (PAGE_SIZE - 1)) == 0)
-		iter->offset -= PAGE_SIZE % obj_size;
+	if ((iter->offset & (GENRADIX_NODE_SIZE - 1)) == 0)
+		iter->offset -= GENRADIX_NODE_SIZE % obj_size;
 
 	iter->offset -= obj_size;
 	iter->pos--;
@@ -263,7 +266,7 @@ static inline void __genradix_iter_rewind(struct genradix_iter *iter,
 	genradix_for_each_from(_radix, _iter, _p, 0)
 
 #define genradix_last_pos(_radix)				\
-	(SIZE_MAX / PAGE_SIZE * __genradix_objs_per_page(_radix) - 1)
+	(SIZE_MAX / GENRADIX_NODE_SIZE * __genradix_objs_per_page(_radix) - 1)
 
 /**
  * genradix_for_each_reverse - iterate over entry in a genradix, reverse order

lib/generic-radix-tree.c

@@ -5,7 +5,7 @@
 #include <linux/gfp.h>
 #include <linux/kmemleak.h>
 
-#define GENRADIX_ARY		(PAGE_SIZE / sizeof(struct genradix_node *))
+#define GENRADIX_ARY		(GENRADIX_NODE_SIZE / sizeof(struct genradix_node *))
 #define GENRADIX_ARY_SHIFT	ilog2(GENRADIX_ARY)
 
 struct genradix_node {
@@ -14,13 +14,13 @@ struct genradix_node {
 		struct genradix_node	*children[GENRADIX_ARY];
 
 		/* Leaf: */
-		u8			data[PAGE_SIZE];
+		u8			data[GENRADIX_NODE_SIZE];
 	};
 };
 
 static inline int genradix_depth_shift(unsigned depth)
 {
-	return PAGE_SHIFT + GENRADIX_ARY_SHIFT * depth;
+	return GENRADIX_NODE_SHIFT + GENRADIX_ARY_SHIFT * depth;
 }
 
 /*
@@ -33,7 +33,7 @@ static inline size_t genradix_depth_size(unsigned depth)
 
 /* depth that's needed for a genradix that can address up to ULONG_MAX: */
 #define GENRADIX_MAX_DEPTH	\
-	DIV_ROUND_UP(BITS_PER_LONG - PAGE_SHIFT, GENRADIX_ARY_SHIFT)
+	DIV_ROUND_UP(BITS_PER_LONG - GENRADIX_NODE_SHIFT, GENRADIX_ARY_SHIFT)
 
 #define GENRADIX_DEPTH_MASK				\
 	((unsigned long) (roundup_pow_of_two(GENRADIX_MAX_DEPTH + 1) - 1))
@@ -79,23 +79,12 @@ EXPORT_SYMBOL(__genradix_ptr);
 
 static inline struct genradix_node *genradix_alloc_node(gfp_t gfp_mask)
 {
-	struct genradix_node *node;
-
-	node = (struct genradix_node *)__get_free_page(gfp_mask|__GFP_ZERO);
-
-	/*
-	 * We're using pages (not slab allocations) directly for kernel data
-	 * structures, so we need to explicitly inform kmemleak of them in order
-	 * to avoid false positive memory leak reports.
-	 */
-	kmemleak_alloc(node, PAGE_SIZE, 1, gfp_mask);
-	return node;
+	return kzalloc(GENRADIX_NODE_SIZE, gfp_mask);
 }
 
 static inline void genradix_free_node(struct genradix_node *node)
 {
-	kmemleak_free(node);
-	free_page((unsigned long)node);
+	kfree(node);
 }
 
 /*
@@ -200,7 +189,7 @@ void *__genradix_iter_peek(struct genradix_iter *iter,
 			i++;
 			iter->offset = round_down(iter->offset + objs_per_ptr,
 						  objs_per_ptr);
-			iter->pos = (iter->offset >> PAGE_SHIFT) *
+			iter->pos = (iter->offset >> GENRADIX_NODE_SHIFT) *
 				objs_per_page;
 			if (i == GENRADIX_ARY)
 				goto restart;
@@ -209,7 +198,7 @@ void *__genradix_iter_peek(struct genradix_iter *iter,
 		n = n->children[i];
 	}
 
-	return &n->data[iter->offset & (PAGE_SIZE - 1)];
+	return &n->data[iter->offset & (GENRADIX_NODE_SIZE - 1)];
 }
 EXPORT_SYMBOL(__genradix_iter_peek);
 
@@ -235,7 +224,7 @@ void *__genradix_iter_peek_prev(struct genradix_iter *iter,
 
 	if (ilog2(iter->offset) >= genradix_depth_shift(level)) {
 		iter->offset = genradix_depth_size(level);
-		iter->pos = (iter->offset >> PAGE_SHIFT) * objs_per_page;
+		iter->pos = (iter->offset >> GENRADIX_NODE_SHIFT) * objs_per_page;
 
 		iter->offset -= obj_size_plus_page_remainder;
 		iter->pos--;
@@ -251,7 +240,7 @@ void *__genradix_iter_peek_prev(struct genradix_iter *iter,
 			size_t objs_per_ptr = genradix_depth_size(level);
 
 			iter->offset = round_down(iter->offset, objs_per_ptr);
-			iter->pos = (iter->offset >> PAGE_SHIFT) * objs_per_page;
+			iter->pos = (iter->offset >> GENRADIX_NODE_SHIFT) * objs_per_page;
 
 			if (!iter->offset)
 				return NULL;
@@ -267,7 +256,7 @@ void *__genradix_iter_peek_prev(struct genradix_iter *iter,
 		n = n->children[i];
 	}
 
-	return &n->data[iter->offset & (PAGE_SIZE - 1)];
+	return &n->data[iter->offset & (GENRADIX_NODE_SIZE - 1)];
 }
 EXPORT_SYMBOL(__genradix_iter_peek_prev);
 
@@ -289,7 +278,7 @@ int __genradix_prealloc(struct __genradix *radix, size_t size,
 {
 	size_t offset;
 
-	for (offset = 0; offset < size; offset += PAGE_SIZE)
+	for (offset = 0; offset < size; offset += GENRADIX_NODE_SIZE)
 		if (!__genradix_ptr_alloc(radix, offset, gfp_mask))
 			return -ENOMEM;