From 26fd8d962ce42b7eb8d1c1eb43ddfa1ff24dc3aa Mon Sep 17 00:00:00 2001
From: John Hawthorn <john@hawthorn.email>
Date: Wed, 20 Nov 2019 14:18:40 -0800
Subject: Optimize pinned page sorting

Previously we would count the pinned objects on each comparison. Since
sorting is O(N log N) and we calculated this on both left and right
pages on each comparison this resulted in a extra iterations over the
slots.
---
 gc.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

(limited to 'gc.c')

diff --git a/gc.c b/gc.c
index 9329f311d2..d2b4330889 100644
--- a/gc.c
+++ b/gc.c
@@ -844,6 +844,7 @@ enum {
 struct heap_page {
     short total_slots;
     short free_slots;
+    short pinned_slots;
     short final_slots;
     struct {
 	unsigned int before_sweep : 1;
@@ -7731,9 +7732,13 @@ count_pinned(struct heap_page *page)
 static int
 compare_pinned(const void *left, const void *right, void *dummy)
 {
-    int left_count = count_pinned(*(struct heap_page * const *)left);
-    int right_count = count_pinned(*(struct heap_page * const *)right);
-    return right_count - left_count;
+    struct heap_page *left_page;
+    struct heap_page *right_page;
+
+    left_page = *(struct heap_page * const *)left;
+    right_page = *(struct heap_page * const *)right;
+
+    return right_page->pinned_slots - left_page->pinned_slots;
 }
 
 static int
@@ -7760,6 +7765,7 @@ allocate_page_list(rb_objspace_t *objspace, page_compare_func_t *comparator)
 
     list_for_each(&heap_eden->pages, page, page_node) {
         page_list[i++] = page;
+        page->pinned_slots = count_pinned(page);
         GC_ASSERT(page != NULL);
     }
     GC_ASSERT(total_pages > 0);
-- 
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