From 9b90fd4f6099a2e714f0f473f819f22c78e129ef Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Sun, 10 Sep 2023 22:39:24 +0900
Subject: [PATCH] gc.c (incremental_sweep_phase): rebuild free pages link only
 if needed

---
 src/gc.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/gc.c b/src/gc.c
index ad491a30e..c94f6c5e6 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -1066,6 +1066,7 @@ incremental_sweep_phase(mrb_state *mrb, mrb_gc *gc, size_t limit)
 {
   mrb_heap_page *page = gc->sweeps;
   size_t tried_sweep = 0;
+  mrb_bool rebuild = FALSE;
 
   while (page && (tried_sweep < limit)) {
     RVALUE *p = objects(page);
@@ -1114,6 +1115,7 @@ incremental_sweep_phase(mrb_state *mrb, mrb_gc *gc, size_t limit)
 
       mrb_free(mrb, page);
       page = next;
+      rebuild = TRUE;
     }
     else {
       if (page->freelist == NULL && is_minor_gc(gc))
@@ -1129,11 +1131,13 @@ incremental_sweep_phase(mrb_state *mrb, mrb_gc *gc, size_t limit)
   gc->sweeps = page;
 
   /* rebuild free_heaps link */
-  gc->free_heaps = NULL;
-  for (mrb_heap_page *p = gc->heaps; p; p=p->next) {
-    if (p->freelist) {
-      p->free_next = gc->free_heaps;
-      gc->free_heaps = p;
+  if (rebuild) {
+    gc->free_heaps = NULL;
+    for (mrb_heap_page *p = gc->heaps; p; p=p->next) {
+      if (p->freelist) {
+        p->free_next = gc->free_heaps;
+        gc->free_heaps = p;
+      }
     }
   }