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

[Justin Lebar]

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

If any testing was done on Firefox with its fork of jemalloc to reach
this conclusion, surely it's no longer valid.

I'd rather stick closer to the stock implementation until we can
demonstrate that changes are beneficial.

>  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
>
> _______________________________________________
> jemalloc-discuss mailing list
> jemalloc-discuss at canonware.com
> http://www.canonware.com/mailman/listinfo/jemalloc-discuss