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6.7 KiB

Make it more likely for the system allocator to release free()d memory arenas on glibc-based systems.
Patch by Charles-François Natali.
https://bugs.python.org/issue20494
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -2,6 +2,13 @@
#ifdef WITH_PYMALLOC
+#ifdef HAVE_MMAP
+ #include <sys/mman.h>
+ #ifdef MAP_ANONYMOUS
+ #define ARENAS_USE_MMAP
+ #endif
+#endif
+
#ifdef WITH_VALGRIND
#include <valgrind/valgrind.h>
@@ -75,7 +82,8 @@ static int running_on_valgrind = -1;
* 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 +115,11 @@ static int running_on_valgrind = -1;
* 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.
*/
/*==========================================================================*/
@@ -143,10 +152,13 @@ static int running_on_valgrind = -1;
* 1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
* 2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
*
+ * Note: a size threshold of 512 guarantees that newly created dictionaries
+ * will be allocated from preallocated memory pools on 64-bit.
+ *
* 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)
/*
@@ -174,15 +186,15 @@ static int running_on_valgrind = -1;
/*
* The allocator sub-allocates <Big> blocks of memory (called arenas) aligned
* on a page boundary. This is a reserved virtual address space for the
- * current process (obtained through a malloc call). In no way this means
- * that the memory arenas will be used entirely. A malloc(<Big>) is usually
- * an address range reservation for <Big> bytes, unless all pages within this
- * space are referenced subsequently. So malloc'ing big blocks and not using
- * them does not mean "wasting memory". It's an addressable range wastage...
+ * current process (obtained through a malloc()/mmap() call). In no way this
+ * means that the memory arenas will be used entirely. A malloc(<Big>) is
+ * usually an address range reservation for <Big> bytes, unless all pages within
+ * this space are referenced subsequently. So malloc'ing big blocks and not
+ * using them does not mean "wasting memory". It's an addressable range
+ * wastage...
*
- * Therefore, allocating arenas with malloc is not optimal, because there is
- * some address space wastage, but this is the most portable way to request
- * memory from the system across various platforms.
+ * Arenas are allocated with mmap() on systems supporting anonymous memory
+ * mappings to reduce heap fragmentation.
*/
#define ARENA_SIZE (256 << 10) /* 256KB */
@@ -440,6 +452,9 @@ static poolp usedpools[2 * ((NB_SMALL_SI
, 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 */
@@ -577,7 +592,12 @@ new_arena(void)
arenaobj = unused_arena_objects;
unused_arena_objects = arenaobj->nextarena;
assert(arenaobj->address == 0);
+#ifdef ARENAS_USE_MMAP
+ arenaobj->address = (uptr)mmap(NULL, ARENA_SIZE, PROT_READ|PROT_WRITE,
+ MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+#else
arenaobj->address = (uptr)malloc(ARENA_SIZE);
+#endif
if (arenaobj->address == 0) {
/* The allocation failed: return NULL after putting the
* arenaobj back.
@@ -1054,7 +1074,11 @@ PyObject_Free(void *p)
unused_arena_objects = ao;
/* Free the entire arena. */
+#ifdef ARENAS_USE_MMAP
+ munmap((void *)ao->address, ARENA_SIZE);
+#else
free((void *)ao->address);
+#endif
ao->address = 0; /* mark unassociated */
--narenas_currently_allocated;
diff --git a/configure b/configure
--- a/configure
+++ b/configure
@@ -10164,7 +10164,7 @@ for ac_func in alarm setitimer getitimer
clock confstr ctermid execv fchmod fchown fork fpathconf ftime ftruncate \
gai_strerror getgroups getlogin getloadavg getpeername getpgid getpid \
getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
- initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime \
+ initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime mmap \
mremap nice pathconf pause plock poll pthread_init \
putenv readlink realpath \
select sem_open sem_timedwait sem_getvalue sem_unlink setegid seteuid \
diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -2905,7 +2905,7 @@ AC_CHECK_FUNCS(alarm setitimer getitimer
clock confstr ctermid execv fchmod fchown fork fpathconf ftime ftruncate \
gai_strerror getgroups getlogin getloadavg getpeername getpgid getpid \
getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
- initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime \
+ initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime mmap \
mremap nice pathconf pause plock poll pthread_init \
putenv readlink realpath \
select sem_open sem_timedwait sem_getvalue sem_unlink setegid seteuid \
diff --git a/pyconfig.h.in b/pyconfig.h.in
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -475,6 +475,9 @@
/* Define to 1 if you have the `mktime' function. */
#undef HAVE_MKTIME
+/* Define to 1 if you have the `mmap' function. */
+#undef HAVE_MMAP
+
/* Define to 1 if you have the `mremap' function. */
#undef HAVE_MREMAP