[patch v4] malloc: avoid need for tcache == NULL checks

[Florian Weimer]

* DJ Delorie:

>  /* Initialize tcache.  In the rare case there isn't any memory available,
>     later calls will retry initialization.  */
>  static void
> -tcache_init (void)
> +tcache_init (mstate av)
>  {
> -  if (tcache_shutting_down)
> +  /* Set this unconditionally to avoid infinite loops.  */
> +  tcache_set_disabled ();
> +  if (mp_.tcache_count == 0)
>      return;
>  
>    size_t bytes = sizeof (tcache_perthread_struct);
> -  tcache = (tcache_perthread_struct *) __libc_malloc2 (bytes);
> +  if (av)
> +    tcache = (tcache_perthread_struct *) _int_malloc (av, request2size (bytes));

I think this is too long.

> +  else
> +    tcache = (tcache_perthread_struct *) __libc_malloc2 (bytes);
>  
> -  if (tcache != NULL)
> +  if (tcache == NULL)
> +    {
> +      /* If the allocation failed, don't try again.  */
> +      tcache_set_disabled ();
> +    }
> +  else

Already set above.

> @@ -4030,10 +4073,14 @@ _int_malloc (mstate av, size_t bytes)
>  	      /* While we're here, if we see other chunks of the same size,
>  		 stash them in the tcache.  */
>  	      size_t tc_idx = csize2tidx (nb);
> -	      if (tcache != NULL && tc_idx < mp_.tcache_small_bins)
> +	      if (tc_idx < mp_.tcache_small_bins)
>  		{
>  		  mchunkptr tc_victim;
>  
> +#if USE_TCACHE
> +		  if (__glibc_unlikely (tcache_inactive ()))
> +		    tcache_init (av);
> +#endif
>  		  /* While bin not empty and tcache not full, copy chunks.  */
>  		  while (tcache->num_slots[tc_idx] != 0 && (tc_victim = *fb) != NULL)
>  		    {

I'm still concerned that tcache_init invalidates *fb because it triggers
consolidation.

Wilco, what do you thinK?

Thanks,
Florian