From 45582d1fb5e076a334fb9c5fd704da9b7312dc5b Mon Sep 17 00:00:00 2001
From: daan <daanl@outlook.com>
Date: Sun, 5 Jan 2020 13:58:49 -0800
Subject: [PATCH] revert a2a9230 (remove empty page removal on search): this is
 not generally valid when concurrent frees do not always add to
 thread_delayed_free.

---
 src/page.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/page.c b/src/page.c
index 0df32f4c..78570ab0 100644
--- a/src/page.c
+++ b/src/page.c
@@ -659,7 +659,9 @@ static void mi_page_init(mi_heap_t* heap, mi_page_t* page, size_t block_size, mi
 static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* pq)
 {
   // search through the pages in "next fit" order
+  mi_page_t* rpage = NULL;
   size_t count = 0;
+  size_t page_free_count = 0;
   mi_page_t* page = pq->first;
   while( page != NULL)
   {
@@ -671,7 +673,20 @@ static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* p
 
     // 1. if the page contains free blocks, we are done
     if (mi_page_immediate_available(page)) {
-      break;  // pick this one
+      // If all blocks are free, we might retire this page instead.
+      // do this at most 8 times to bound allocation time.
+      // (note: this can happen if a page was earlier not retired due
+      //  to having neighbours that were mostly full or due to concurrent frees)
+      if (page_free_count < 8 && mi_page_all_free(page)) {
+        page_free_count++;
+        if (rpage != NULL) _mi_page_free(rpage,pq,false);
+        rpage = page;
+        page = next;
+        continue;     // and keep looking
+      }
+      else {
+        break;  // pick this one
+      }
     }
 
     // 2. Try to extend
@@ -691,6 +706,14 @@ static mi_page_t* mi_page_queue_find_free_ex(mi_heap_t* heap, mi_page_queue_t* p
 
   mi_stat_counter_increase(heap->tld->stats.searches,count);
 
+  if (page == NULL) {
+    page = rpage;
+    rpage = NULL;
+  }
+  if (rpage != NULL) {
+    _mi_page_free(rpage,pq,false);
+  }
+
   if (page == NULL) {
     page = mi_page_fresh(heap, pq);
   }