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158 lines
6.7 KiB
158 lines
6.7 KiB
6 years ago
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Make it more likely for the system allocator to release free()d memory arenas on glibc-based systems.
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Patch by Charles-François Natali.
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https://bugs.python.org/issue20494
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diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
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--- a/Objects/obmalloc.c
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+++ b/Objects/obmalloc.c
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@@ -2,6 +2,13 @@
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#ifdef WITH_PYMALLOC
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+#ifdef HAVE_MMAP
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+ #include <sys/mman.h>
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+ #ifdef MAP_ANONYMOUS
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+ #define ARENAS_USE_MMAP
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+ #endif
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+#endif
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+
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#ifdef WITH_VALGRIND
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#include <valgrind/valgrind.h>
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@@ -75,7 +82,8 @@ static int running_on_valgrind = -1;
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* Allocation strategy abstract:
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*
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* For small requests, the allocator sub-allocates <Big> blocks of memory.
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- * Requests greater than 256 bytes are routed to the system's allocator.
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+ * Requests greater than SMALL_REQUEST_THRESHOLD bytes are routed to the
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+ * system's allocator.
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*
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* Small requests are grouped in size classes spaced 8 bytes apart, due
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* to the required valid alignment of the returned address. Requests of
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@@ -107,10 +115,11 @@ static int running_on_valgrind = -1;
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* 57-64 64 7
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* 65-72 72 8
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* ... ... ...
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- * 241-248 248 30
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- * 249-256 256 31
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+ * 497-504 504 62
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+ * 505-512 512 63
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*
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- * 0, 257 and up: routed to the underlying allocator.
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+ * 0, SMALL_REQUEST_THRESHOLD + 1 and up: routed to the underlying
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+ * allocator.
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*/
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/*==========================================================================*/
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@@ -143,10 +152,13 @@ static int running_on_valgrind = -1;
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* 1) ALIGNMENT <= SMALL_REQUEST_THRESHOLD <= 256
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* 2) SMALL_REQUEST_THRESHOLD is evenly divisible by ALIGNMENT
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*
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+ * Note: a size threshold of 512 guarantees that newly created dictionaries
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+ * will be allocated from preallocated memory pools on 64-bit.
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+ *
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* Although not required, for better performance and space efficiency,
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* it is recommended that SMALL_REQUEST_THRESHOLD is set to a power of 2.
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*/
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-#define SMALL_REQUEST_THRESHOLD 256
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+#define SMALL_REQUEST_THRESHOLD 512
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#define NB_SMALL_SIZE_CLASSES (SMALL_REQUEST_THRESHOLD / ALIGNMENT)
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/*
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@@ -174,15 +186,15 @@ static int running_on_valgrind = -1;
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/*
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* The allocator sub-allocates <Big> blocks of memory (called arenas) aligned
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* on a page boundary. This is a reserved virtual address space for the
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- * current process (obtained through a malloc call). In no way this means
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- * that the memory arenas will be used entirely. A malloc(<Big>) is usually
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- * an address range reservation for <Big> bytes, unless all pages within this
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- * space are referenced subsequently. So malloc'ing big blocks and not using
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- * them does not mean "wasting memory". It's an addressable range wastage...
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+ * current process (obtained through a malloc()/mmap() call). In no way this
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+ * means that the memory arenas will be used entirely. A malloc(<Big>) is
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+ * usually an address range reservation for <Big> bytes, unless all pages within
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+ * this space are referenced subsequently. So malloc'ing big blocks and not
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+ * using them does not mean "wasting memory". It's an addressable range
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+ * wastage...
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*
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- * Therefore, allocating arenas with malloc is not optimal, because there is
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- * some address space wastage, but this is the most portable way to request
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- * memory from the system across various platforms.
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+ * Arenas are allocated with mmap() on systems supporting anonymous memory
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+ * mappings to reduce heap fragmentation.
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*/
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#define ARENA_SIZE (256 << 10) /* 256KB */
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@@ -440,6 +452,9 @@ static poolp usedpools[2 * ((NB_SMALL_SI
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, PT(48), PT(49), PT(50), PT(51), PT(52), PT(53), PT(54), PT(55)
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#if NB_SMALL_SIZE_CLASSES > 56
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, PT(56), PT(57), PT(58), PT(59), PT(60), PT(61), PT(62), PT(63)
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+#if NB_SMALL_SIZE_CLASSES > 64
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+#error "NB_SMALL_SIZE_CLASSES should be less than 64"
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+#endif /* NB_SMALL_SIZE_CLASSES > 64 */
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#endif /* NB_SMALL_SIZE_CLASSES > 56 */
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#endif /* NB_SMALL_SIZE_CLASSES > 48 */
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#endif /* NB_SMALL_SIZE_CLASSES > 40 */
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@@ -577,7 +592,12 @@ new_arena(void)
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arenaobj = unused_arena_objects;
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unused_arena_objects = arenaobj->nextarena;
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assert(arenaobj->address == 0);
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+#ifdef ARENAS_USE_MMAP
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+ arenaobj->address = (uptr)mmap(NULL, ARENA_SIZE, PROT_READ|PROT_WRITE,
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+ MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
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+#else
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arenaobj->address = (uptr)malloc(ARENA_SIZE);
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+#endif
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if (arenaobj->address == 0) {
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/* The allocation failed: return NULL after putting the
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* arenaobj back.
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@@ -1054,7 +1074,11 @@ PyObject_Free(void *p)
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unused_arena_objects = ao;
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/* Free the entire arena. */
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+#ifdef ARENAS_USE_MMAP
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+ munmap((void *)ao->address, ARENA_SIZE);
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+#else
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free((void *)ao->address);
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+#endif
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ao->address = 0; /* mark unassociated */
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--narenas_currently_allocated;
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diff --git a/configure b/configure
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--- a/configure
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+++ b/configure
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@@ -10164,7 +10164,7 @@ for ac_func in alarm setitimer getitimer
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clock confstr ctermid execv fchmod fchown fork fpathconf ftime ftruncate \
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gai_strerror getgroups getlogin getloadavg getpeername getpgid getpid \
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getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
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- initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime \
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+ initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime mmap \
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mremap nice pathconf pause plock poll pthread_init \
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putenv readlink realpath \
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select sem_open sem_timedwait sem_getvalue sem_unlink setegid seteuid \
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diff --git a/configure.ac b/configure.ac
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--- a/configure.ac
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+++ b/configure.ac
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@@ -2905,7 +2905,7 @@ AC_CHECK_FUNCS(alarm setitimer getitimer
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clock confstr ctermid execv fchmod fchown fork fpathconf ftime ftruncate \
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gai_strerror getgroups getlogin getloadavg getpeername getpgid getpid \
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getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \
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- initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime \
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+ initgroups kill killpg lchmod lchown lstat mkfifo mknod mktime mmap \
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mremap nice pathconf pause plock poll pthread_init \
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putenv readlink realpath \
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select sem_open sem_timedwait sem_getvalue sem_unlink setegid seteuid \
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diff --git a/pyconfig.h.in b/pyconfig.h.in
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--- a/pyconfig.h.in
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+++ b/pyconfig.h.in
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@@ -475,6 +475,9 @@
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/* Define to 1 if you have the `mktime' function. */
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#undef HAVE_MKTIME
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+/* Define to 1 if you have the `mmap' function. */
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+#undef HAVE_MMAP
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+
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/* Define to 1 if you have the `mremap' function. */
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#undef HAVE_MREMAP
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