[3.15] gh-161420: Process mimalloc's delayed frees on every generic malloc again (gh-161533)

Misc/NEWS.d/next/Core_and_Builtins/2026-11-07-09-30-00.gh-issue-161420.mIdFre.rst

@@ -0,0 +1,2 @@
+Restore ``mimalloc``'s previous behavior of processing delayed frees from other
+threads on every generic malloc call, reverting the change introduced in v2.2.2.

Objects/mimalloc/page.c

@@ -1071,16 +1071,19 @@ void* _mi_malloc_generic(mi_heap_t* heap, size_t size, bool zero, size_t huge_al
   }
   mi_assert_internal(mi_heap_is_initialized(heap));
 
+  // Process delayed frees from other threads (but skip contended ones).
+  // CPython: gh-161420 showed that calling _mi_heap_delayed_free_partial only
+  // once every 100 generic malloc calls led to high memory usage.
+  // To avoid this, we now process delayed frees on every generic malloc call again.
+  _mi_heap_delayed_free_partial(heap);
+
   // do administrative tasks every N generic mallocs
   if mi_unlikely(++heap->generic_count >= 100) {
     heap->generic_collect_count += heap->generic_count;
     heap->generic_count = 0;
     // call potential deferred free routines
     _mi_deferred_free(heap, false);
 
-    // free delayed frees from other threads (but skip contended ones)
-    _mi_heap_delayed_free_partial(heap);
-
     // collect every once in a while (10000 by default)
     const long generic_collect = mi_option_get_clamp(mi_option_generic_collect, 1, 1000000L);
     if (heap->generic_collect_count >= generic_collect) {