mimalloc: minimal changes for use in Python

 - remove debug spam for freeing large allocations
 - use same bytes (0xDD) for freed allocations in CPython and mimalloc
   This is important for the test_capi debug memory tests

Author: colesbury

Include/mimalloc/mimalloc/types.h

@@ -524,7 +524,7 @@ struct mi_heap_s {
 #define MI_DEBUG_UNINIT     (0xD0)
 #endif
 #if !defined(MI_DEBUG_FREED)
-#define MI_DEBUG_FREED      (0xDF)
+#define MI_DEBUG_FREED      (0xDD)
 #endif
 #if !defined(MI_DEBUG_PADDING)
 #define MI_DEBUG_PADDING    (0xDE)

Objects/mimalloc/alloc.c

@@ -533,7 +533,7 @@ static inline mi_segment_t* mi_checked_ptr_segment(const void* p, const char* ms
   mi_segment_t* const segment = _mi_ptr_segment(p);
   mi_assert_internal(segment != NULL);
 
-#if (MI_DEBUG>0)
+#if 0 && (MI_DEBUG>0)
   if mi_unlikely(!mi_is_in_heap_region(p)) {
   #if (MI_INTPTR_SIZE == 8 && defined(__linux__))
     if (((uintptr_t)p >> 40) != 0x7F) { // linux tends to align large blocks above 0x7F000000000 (issue #640)

Objects/mimalloc/os.c

@@ -240,7 +240,8 @@ static void* mi_os_prim_alloc_aligned(size_t size, size_t alignment, bool commit
   }
   else {
     // if not aligned, free it, overallocate, and unmap around it
-    _mi_warning_message("unable to allocate aligned OS memory directly, fall back to over-allocation (size: 0x%zx bytes, address: %p, alignment: 0x%zx, commit: %d)\n", size, p, alignment, commit);
+    // NOTE(sgross): this warning causes issues in Python tests
+    // _mi_warning_message("unable to allocate aligned OS memory directly, fall back to over-allocation (size: 0x%zx bytes, address: %p, alignment: 0x%zx, commit: %d)\n", size, p, alignment, commit);
     mi_os_prim_free(p, size, commit, stats);
     if (size >= (SIZE_MAX - alignment)) return NULL; // overflow
     const size_t over_size = size + alignment;