malloc: Trim unused arenas on thread exit

[Siddhesh Poyarekar]

On Wednesday 15 November 2017 07:06 PM, Florian Weimer wrote:
> Here's a patch which does just that.  Tested with and without
> --disable-experimental-malloc.
> 
> It doesn't have any consolidation/trimming changes.

LGTM, I trust you'll write a nice git commit log to explain the change :)

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

> 
> malloc-shutdown.patch
> 
> 
> malloc: Use a single thread shutdown hook for tcache and arenas
> 
> This modifies the code to make the ordering explicit (tcache first).
> 
> 2017-11-15  Florian Weimer  <fweimer@redhat.com>
> 
> 	* malloc/malloc.c (tcache_thread_shutdown): Rename from
> 	tcache_thread_freeres.  Define for USE_TCACHE and !USE_TCACHE
> 	alike.  Remove freeres marker.
> 	* malloc/arena.c (arena_thread_freeres): Call
> 	tcache_thread_shutdown.
> 
> diff --git a/malloc/arena.c b/malloc/arena.c
> index 85b985e193..4d27e17c46 100644
> --- a/malloc/arena.c
> +++ b/malloc/arena.c
> @@ -944,6 +944,11 @@ arena_get_retry (mstate ar_ptr, size_t bytes)
>  static void __attribute__ ((section ("__libc_thread_freeres_fn")))
>  arena_thread_freeres (void)
>  {
> +  /* Shut down the thread cache first.  This could deallocate data for
> +     the thread arena, so do this before we put the arena on the free
> +     list.  */
> +  tcache_thread_shutdown ();
> +
>    mstate a = thread_arena;
>    thread_arena = NULL;
>  
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 2999ac4d2f..79f0e9eac7 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -1869,6 +1869,9 @@ void *weak_variable (*__memalign_hook)
>    = memalign_hook_ini;
>  void weak_variable (*__after_morecore_hook) (void) = NULL;
>  
> +/* This function is called from the arena shutdown hook, to free the
> +   thread cache (if it exists).  */
> +static void tcache_thread_shutdown (void);
>  
>  /* ------------------ Testing support ----------------------------------*/
>  
> @@ -2938,8 +2941,8 @@ tcache_get (size_t tc_idx)
>    return (void *) e;
>  }
>  
> -static void __attribute__ ((section ("__libc_thread_freeres_fn")))
> -tcache_thread_freeres (void)
> +static void
> +tcache_thread_shutdown (void)
>  {
>    int i;
>    tcache_perthread_struct *tcache_tmp = tcache;
> @@ -2965,7 +2968,6 @@ tcache_thread_freeres (void)
>  
>    __libc_free (tcache_tmp);
>  }
> -text_set_element (__libc_thread_subfreeres, tcache_thread_freeres);
>  
>  static void
>  tcache_init(void)
> @@ -3002,13 +3004,20 @@ tcache_init(void)
>  
>  }
>  
> -#define MAYBE_INIT_TCACHE() \
> +# define MAYBE_INIT_TCACHE() \
>    if (__glibc_unlikely (tcache == NULL)) \
>      tcache_init();
>  
> -#else
> -#define MAYBE_INIT_TCACHE()
> -#endif
> +#else  /* !USE_TCACHE */
> +# define MAYBE_INIT_TCACHE()
> +
> +static void
> +tcache_thread_shutdown (void)
> +{
> +  /* Nothing to do if there is no thread cache.  */
> +}
> +
> +#endif /* !USE_TCACHE  */
>  
>  void *
>  __libc_malloc (size_t bytes)
>