[PATCH] Add a build option to freeze the number of arenas to 1

[Mike Hommey]

From: Mike Hommey <mh at glandium.org>

---

Mozilla does not currently make extensive use of concurrent allocation,
so the increased fragmentation associated with multiple arenas is not
warranted.

 configure.ac                                     |    4 ++++
 include/jemalloc/internal/jemalloc_internal.h.in |    8 ++++++++
 include/jemalloc/jemalloc_defs.h.in              |    3 +++
 src/jemalloc.c                                   |   10 ++++++++++
 4 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/configure.ac b/configure.ac
index 704a703..4cc7d6f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -787,6 +787,10 @@ if test "x${enable_tls}" = "x0" ; then
   AC_DEFINE_UNQUOTED([NO_TLS], [ ])
 fi
 
+AC_ARG_WITH([one_arena],
+  [AS_HELP_STRING([--with-one-arena], [Force jemalloc to use only one arena])],
+  [AC_DEFINE([JEMALLOC_ONE_ARENA])])
+
 dnl ============================================================================
 dnl Check for ffsl(3), and fail if not found.  This function exists on all
 dnl platforms that jemalloc currently has a chance of functioning on without
diff --git a/include/jemalloc/internal/jemalloc_internal.h.in b/include/jemalloc/internal/jemalloc_internal.h.in
index 971336e..75b4b66 100644
--- a/include/jemalloc/internal/jemalloc_internal.h.in
+++ b/include/jemalloc/internal/jemalloc_internal.h.in
@@ -384,7 +384,11 @@ extern bool	opt_junk;
 extern bool	opt_sysv;
 extern bool	opt_xmalloc;
 extern bool	opt_zero;
+#ifdef JEMALLOC_ONE_ARENA
+static const size_t	opt_narenas = 1;
+#else
 extern size_t	opt_narenas;
+#endif
 
 #ifdef DYNAMIC_PAGE_SHIFT
 extern size_t		pagesize;
@@ -420,7 +424,11 @@ extern __thread arena_t	*arenas_tls JEMALLOC_ATTR(tls_model("initial-exec"));
  * arenas array are necessarily used; arenas are created lazily as needed.
  */
 extern arena_t		**arenas;
+#ifdef JEMALLOC_ONE_ARENA
+static const unsigned	narenas = 1;
+#else
 extern unsigned		narenas;
+#endif
 
 #ifndef NO_TLS
 extern __thread thread_allocated_t	thread_allocated_tls;
diff --git a/include/jemalloc/jemalloc_defs.h.in b/include/jemalloc/jemalloc_defs.h.in
index 18cad28..e7e12d5 100644
--- a/include/jemalloc/jemalloc_defs.h.in
+++ b/include/jemalloc/jemalloc_defs.h.in
@@ -128,6 +128,9 @@
 /* TLS is used to map arenas and magazine caches to threads. */
 #undef NO_TLS
 
+/* Forces jemalloc to use only one arena when defined */
+#undef JEMALLOC_ONE_ARENA
+
 /*
  * JEMALLOC_IVSALLOC enables ivsalloc(), which verifies that pointers reside
  * within jemalloc-owned chunks before dereferencing them.
diff --git a/src/jemalloc.c b/src/jemalloc.c
index 8b927f8..540f211 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -6,7 +6,9 @@
 
 malloc_mutex_t		arenas_lock;
 arena_t			**arenas;
+#ifndef JEMALLOC_ONE_ARENA
 unsigned		narenas;
+#endif
 
 pthread_key_t		arenas_tsd;
 #ifndef NO_TLS
@@ -51,7 +53,9 @@ bool	opt_junk = false;
 bool	opt_sysv = false;
 bool	opt_xmalloc = false;
 bool	opt_zero = false;
+#ifndef JEMALLOC_ONE_ARENA
 size_t	opt_narenas = 0;
+#endif
 
 /******************************************************************************/
 /* Function prototypes for non-inline static functions. */
@@ -573,7 +577,9 @@ malloc_conf_init(void)
 			 */
 			CONF_HANDLE_SIZE_T(lg_chunk, PAGE_SHIFT+1,
 			    (sizeof(size_t) << 3) - 1)
+#ifndef JEMALLOC_ONE_ARENA
 			CONF_HANDLE_SIZE_T(narenas, 1, SIZE_T_MAX)
+#endif
 			CONF_HANDLE_SSIZE_T(lg_dirty_mult, -1,
 			    (sizeof(size_t) << 3) - 1)
 			CONF_HANDLE_BOOL(stats_print)
@@ -745,7 +751,9 @@ malloc_init_hard(void)
 	 * Create enough scaffolding to allow recursive allocation in
 	 * malloc_ncpus().
 	 */
+#ifndef JEMALLOC_ONE_ARENA
 	narenas = 1;
+#endif
 	arenas = init_arenas;
 	memset(arenas, 0, sizeof(arena_t *) * narenas);
 
@@ -778,6 +786,7 @@ malloc_init_hard(void)
 	ncpus = malloc_ncpus();
 	malloc_mutex_lock(&init_lock);
 
+#ifndef JEMALLOC_ONE_ARENA
 	if (opt_narenas == 0) {
 		/*
 		 * For SMP systems, create more than one arena per CPU by
@@ -802,6 +811,7 @@ malloc_init_hard(void)
 		malloc_write(u2s(narenas, 10, buf));
 		malloc_write(")\n");
 	}
+#endif
 
 	/* Allocate and initialize arenas. */
 	arenas = (arena_t **)base_alloc(sizeof(arena_t *) * narenas);
-- 
1.7.9.1