add region collection

include/mimalloc-internal.h

@@ -54,6 +54,8 @@ bool       _mi_mem_commit(void* p, size_t size, mi_stats_t* stats);
 bool       _mi_mem_protect(void* addr, size_t size);
 bool       _mi_mem_unprotect(void* addr, size_t size);
 
+void        _mi_mem_collect(mi_stats_t* stats);
+
 // "segment.c"
 mi_page_t* _mi_segment_page_alloc(size_t block_wsize, mi_segments_tld_t* tld, mi_os_tld_t* os_tld);
 void       _mi_segment_page_free(mi_page_t* page, bool force, mi_segments_tld_t* tld);

src/heap.c

@@ -147,6 +147,11 @@ static void mi_heap_collect_ex(mi_heap_t* heap, mi_collect_t collect)
   if (collect >= FORCE) {
     _mi_segment_thread_collect(&heap->tld->segments);
   }
+
+  // collect regions
+  if (collect >= FORCE && _mi_is_main_thread()) {
+    _mi_mem_collect(&heap->tld->stats);
+  }
 }
 
 void _mi_heap_collect_abandon(mi_heap_t* heap) {

src/memory.c

@@ -336,6 +336,31 @@ void _mi_mem_free(void* p, size_t size, size_t id, mi_stats_t* stats) {
   }
 }
 
+
+/* ----------------------------------------------------------------------------
+  collection
+-----------------------------------------------------------------------------*/
+void _mi_mem_collect(mi_stats_t* stats) {
+  // free every region that has no segments in use.
+  for (size_t i = 0; i < regions_count; i++) {
+    mem_region_t* region = &regions[i];
+    if (mi_atomic_read(&region->map) == 0 && region->start != NULL) {  
+      // if no segments used, try to claim the whole region
+      uintptr_t m;
+      do {
+        m = mi_atomic_read(&region->map);
+      } while(m == 0 && !mi_atomic_compare_exchange(&region->map, ~((uintptr_t)0), 0 ));
+      if (m == 0) {
+        // on success, free the whole region
+        if (region->start != NULL) _mi_os_free((void*)region->start, MI_REGION_SIZE, stats);
+        // and release 
+        region->start = 0;
+        mi_atomic_write(&region->map,0);
+      }
+    }
+  }
+}
+
 /* ----------------------------------------------------------------------------
   Other
 -----------------------------------------------------------------------------*/

test/test-stress.c

@@ -36,6 +36,7 @@ static void* alloc_items(size_t items) {
   if ((rand()%100) == 0) items *= 100; // 1% huge objects;
   if (items==40) items++;              // pthreads uses that size for stack increases
   uintptr_t* p = mi_mallocn_tp(uintptr_t,items);
+  if(p == NULL) return NULL;
   for (uintptr_t i = 0; i < items; i++) p[i] = (items - i) ^ cookie;
   return p;
 }