https://github.com/python/cpython/commit/b8dd06f1d6ee3b172c58d688f122b29bb2582f9a
commit: b8dd06f1d6ee3b172c58d688f122b29bb2582f9a
branch: main
author: Maik Schulze <[email protected]>
committer: corona10 <[email protected]>
date: 2026-11-07T07:21:14Z
summary:
gh-161420: Process mimalloc's delayed frees on every generic malloc again
(gh-161533)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-11-07-09-30-00.gh-issue-161420.mIdFre.rst
M Objects/mimalloc/page.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-11-07-09-30-00.gh-issue-161420.mIdFre.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-11-07-09-30-00.gh-issue-161420.mIdFre.rst
new file mode 100644
index 000000000000000..296a2267f397be0
--- /dev/null
+++
b/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.
diff --git a/Objects/mimalloc/page.c b/Objects/mimalloc/page.c
index 4bce8ce76044cbe..2f26d04aaaa4d87 100644
--- a/Objects/mimalloc/page.c
+++ b/Objects/mimalloc/page.c
@@ -1071,6 +1071,12 @@ 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;
@@ -1078,9 +1084,6 @@ void* _mi_malloc_generic(mi_heap_t* heap, size_t size,
bool zero, size_t huge_al
// 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) {
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