From: James Jones <jejones3141@gmail.com>
Date: Fri, 27 Aug 2021 15:44:41 +0000 (-0500)
Subject: Adjust initial LST pivot stack size in accordance with initial size (#4213)
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8958ab5c956aba8aa18c4e297def90f5c5b81bc6;p=thirdparty%2Ffreeradius-server.git

Adjust initial LST pivot stack size in accordance with initial size (#4213)

It's now initially max(1, log2(initial array size)).
---

diff --git a/src/lib/util/lst.c b/src/lib/util/lst.c
index e36190fe2ab..f5d930b34f1 100644
--- a/src/lib/util/lst.c
+++ b/src/lib/util/lst.c
@@ -46,7 +46,6 @@ RCSID("$Id$")
  * the pivot stack may be a rare event.
  */
 #define INITIAL_CAPACITY	2048
-#define INITIAL_STACK_CAPACITY	32
 
 #define is_power_of_2(_n)	((_n) && (((_n) & ((_n) - 1)) == 0))
 
@@ -224,6 +223,7 @@ fr_lst_t *_fr_lst_alloc(TALLOC_CTX *ctx, fr_lst_cmp_t cmp, char const *type, siz
 {
 	fr_lst_t	*lst;
 	pivot_stack_t	*s;
+	unsigned int	initial_stack_capacity;
 
 	if (!init) {
 		init = INITIAL_CAPACITY;
@@ -231,6 +231,8 @@ fr_lst_t *_fr_lst_alloc(TALLOC_CTX *ctx, fr_lst_cmp_t cmp, char const *type, siz
 		init = 1 << fr_high_bit_pos(init);
 	}
 
+	for (initial_stack_capacity = 1; (1U << initial_stack_capacity) < init; initial_stack_capacity++) ;
+
 	/*
 	 *	Pre-allocate stack memory as it is
 	 *	unlikely to need to grow in practice.
@@ -243,7 +245,7 @@ fr_lst_t *_fr_lst_alloc(TALLOC_CTX *ctx, fr_lst_cmp_t cmp, char const *type, siz
 	 *	Pre-allocating three chunks appears to be
 	 *	the optimum.
 	 */
-	lst = talloc_zero_pooled_object(ctx, fr_lst_t, 3, (INITIAL_STACK_CAPACITY * sizeof(fr_lst_index_t)));
+	lst = talloc_zero_pooled_object(ctx, fr_lst_t, 3, (initial_stack_capacity * sizeof(fr_lst_index_t)));
 	if (unlikely(!lst)) return NULL;
 
 	lst->capacity = init;
@@ -258,10 +260,10 @@ fr_lst_t *_fr_lst_alloc(TALLOC_CTX *ctx, fr_lst_cmp_t cmp, char const *type, siz
 	 *	Allocate the initial stack
 	 */
 	s = &lst->s;
-	s->data = talloc_array(lst, fr_lst_index_t, INITIAL_STACK_CAPACITY);
+	s->data = talloc_array(lst, fr_lst_index_t, initial_stack_capacity);
 	if (unlikely(!s->data)) goto cleanup;
 	s->depth = 0;
-	s->size = INITIAL_STACK_CAPACITY;
+	s->size = initial_stack_capacity;
 
 	/* Initially the LST is empty and we start at the beginning of the array */
 	stack_push(lst, &lst->s, 0);
diff --git a/src/lib/util/lst_tests.c b/src/lib/util/lst_tests.c
index 15686aadd48..68830728e60 100644
--- a/src/lib/util/lst_tests.c
+++ b/src/lib/util/lst_tests.c
@@ -260,7 +260,8 @@ static void lst_burn_in(void)
 	array = calloc(BURN_IN_OPS, sizeof(lst_thing));
 	for (unsigned int i = 0; i < BURN_IN_OPS; i++) array[i].data = rand() % 65537;
 
-	lst = fr_lst_alloc(NULL, lst_cmp, lst_thing, idx, 0);
+	/* Make init small to exercise growing the pivot stack. */
+	lst = fr_lst_alloc(NULL, lst_cmp, lst_thing, idx, 32);
 
 	for (unsigned int i = 0; i < BURN_IN_OPS; i++) {
 		lst_thing	*ret_thing = NULL;