Pre-allocate LST stack memory

This is mostly to ensure good locality

diff --git a/src/lib/util/lst.c b/src/lib/util/lst.c
index c44d7fd5c01d8dfe757d32f5db1318bbf2e6c6a2..4c39734e5fdea9a8118fb29bedb64a19d55ba6b1 100644 (file)
--- a/src/lib/util/lst.c
+++ b/src/lib/util/lst.c
@@ -144,7 +144,7 @@ bool is_bucket(fr_lst_t *lst, stack_index_t idx)
  * 2. one can fetch and modify arbitrary stack items; when array elements must be
  *    moved to keep them contiguous, the pivot stack entries must change to match.
  */
-static pivot_stack_t *stack_alloc(TALLOC_CTX *ctx)
+static inline CC_HINT(always_inline, nonnull) pivot_stack_t *stack_alloc(TALLOC_CTX *ctx)
 {
        pivot_stack_t   *s;
 
@@ -230,8 +230,18 @@ fr_lst_t *_fr_lst_alloc(TALLOC_CTX *ctx, fr_lst_cmp_t cmp, char const *type, siz
 {
        fr_lst_t        *lst;
 
-       lst = talloc_zero(ctx, fr_lst_t);
-       if (!lst) return NULL;
+       /*
+        *      Pre-allocate stack memory as it is
+        *      unlikely to need to grow in practice.
+        *
+        *      We don't pre-allocate the array of elements
+        *      If we pre-allocated the array of elements
+        *      we'd end up wasting that memory as soon as
+        *      we needed to expand the array.
+        */
+       lst = talloc_zero_pooled_object(ctx, fr_lst_t, 2,
+                                       sizeof(pivot_stack_t) + (INITIAL_STACK_CAPACITY * sizeof(fr_lst_index_t)));
+       if (unlikely(!lst)) return NULL;
 
        lst->capacity = INITIAL_CAPACITY;
        lst->p = talloc_array(lst, void *, lst->capacity);