diff --git a/src/init.c b/src/init.c
index 18a18f60..366acbf5 100644
--- a/src/init.c
+++ b/src/init.c
@@ -140,6 +140,7 @@ mi_stats_t _mi_stats_main = { MI_STATS_NULL };
   Initialization and freeing of the thread local heaps
 ----------------------------------------------------------- */
 
+// note: in x64 in release build `sizeof(mi_thread_data_t)` is under 4KiB (= OS page size).
 typedef struct mi_thread_data_s {
   mi_heap_t  heap;  // must come first due to cast in `_mi_heap_done`
   mi_tld_t   tld;
@@ -154,12 +155,13 @@ static bool _mi_heap_init(void) {
     mi_assert_internal(_mi_heap_default->tld->heap_backing == mi_get_default_heap());
   }
   else {
-    // use `_mi_os_alloc` to allocate directly from the OS
+    // use `_mi_os_alloc` to allocate directly from the OS    
     mi_thread_data_t* td = (mi_thread_data_t*)_mi_os_alloc(sizeof(mi_thread_data_t),&_mi_stats_main); // Todo: more efficient allocation?
     if (td == NULL) {
       _mi_error_message(ENOMEM, "failed to allocate thread local heap memory\n");
       return false;
     }
+    // OS allocated so already zero initialized
     mi_tld_t*  tld = &td->tld;
     mi_heap_t* heap = &td->heap;
     memcpy(heap, &_mi_heap_empty, sizeof(*heap));
@@ -168,8 +170,7 @@ static bool _mi_heap_init(void) {
     heap->cookie = _mi_heap_random_next(heap) | 1;
     heap->key[0] = _mi_heap_random_next(heap);
     heap->key[1] = _mi_heap_random_next(heap);
-    heap->tld = tld;
-    memset(tld, 0, sizeof(*tld));
+    heap->tld = tld;    
     tld->heap_backing = heap;
     tld->segments.stats = &tld->stats;
     tld->segments.os = &tld->os;
diff --git a/src/segment.c b/src/segment.c
index a26ac449..f6554520 100644
--- a/src/segment.c
+++ b/src/segment.c
@@ -948,6 +948,7 @@ static mi_segment_t* mi_abandoned_pop(void) {
   // Do a pop. We use a reader count to prevent
   // a segment to be decommitted while a read is still pending, 
   // and a tagged pointer to prevent A-B-A link corruption.
+  // (this is called from `memory.c:_mi_mem_free` for example)
   mi_atomic_increment(&abandoned_readers);  // ensure no segment gets decommitted
   mi_tagged_segment_t next = 0;
   do {