Issue #11849: Make it more likely for the system allocator to release
free()d memory arenas on glibc-based systems. Patch by Charles-François
Natali.
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 483847c..9a7c7e7 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -2,6 +2,10 @@
#ifdef WITH_PYMALLOC
+#ifdef HAVE_MALLOPT_MMAP_THRESHOLD
+ #include <malloc.h>
+#endif
+
#ifdef WITH_VALGRIND
#include <valgrind/valgrind.h>
@@ -75,7 +79,8 @@
* Allocation strategy abstract:
*
* For small requests, the allocator sub-allocates <Big> blocks of memory.
- * Requests greater than 256 bytes are routed to the system's allocator.
+ * Requests greater than SMALL_REQUEST_THRESHOLD bytes are routed to the
+ * system's allocator.
*
* Small requests are grouped in size classes spaced 8 bytes apart, due
* to the required valid alignment of the returned address. Requests of
@@ -107,10 +112,11 @@
* 57-64 64 7
* 65-72 72 8
* ... ... ...
- * 241-248 248 30
- * 249-256 256 31
+ * 497-504 504 62
+ * 505-512 512 63
*
- * 0, 257 and up: routed to the underlying allocator.
+ * 0, SMALL_REQUEST_THRESHOLD + 1 and up: routed to the underlying
+ * allocator.
*/
/*==========================================================================*/
@@ -139,14 +145,17 @@
* small enough in order to use preallocated memory pools. You can tune
* this value according to your application behaviour and memory needs.
*
+ * Note: a size threshold of 512 guarantees that newly created dictionaries
+ * will be allocated from preallocated memory pools on 64-bit.
+ *
* The following invariants must hold:
- * 1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
+ * 1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 512
* 2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
*
* Although not required, for better performance and space efficiency,
* it is recommended that SMALL_REQUEST_THRESHOLD is set to a power of 2.
*/
-#define SMALL_REQUEST_THRESHOLD 256
+#define SMALL_REQUEST_THRESHOLD 512
#define NB_SMALL_SIZE_CLASSES (SMALL_REQUEST_THRESHOLD / ALIGNMENT)
/*
@@ -440,6 +449,9 @@
, PT(48), PT(49), PT(50), PT(51), PT(52), PT(53), PT(54), PT(55)
#if NB_SMALL_SIZE_CLASSES > 56
, PT(56), PT(57), PT(58), PT(59), PT(60), PT(61), PT(62), PT(63)
+#if NB_SMALL_SIZE_CLASSES > 64
+#error "NB_SMALL_SIZE_CLASSES should be less than 64"
+#endif /* NB_SMALL_SIZE_CLASSES > 64 */
#endif /* NB_SMALL_SIZE_CLASSES > 56 */
#endif /* NB_SMALL_SIZE_CLASSES > 48 */
#endif /* NB_SMALL_SIZE_CLASSES > 40 */
@@ -545,6 +557,11 @@
if (numarenas > PY_SIZE_MAX / sizeof(*arenas))
return NULL; /* overflow */
#endif
+#ifdef HAVE_MALLOPT_MMAP_THRESHOLD
+ /* Ensure arenas are allocated by mmap to avoid heap fragmentation. */
+ if (numarenas == INITIAL_ARENA_OBJECTS)
+ mallopt(M_MMAP_THRESHOLD, ARENA_SIZE);
+#endif
nbytes = numarenas * sizeof(*arenas);
arenaobj = (struct arena_object *)realloc(arenas, nbytes);
if (arenaobj == NULL)