[PATCH] Created tunable to force small pages on stack allocation.

[Cupertino Miranda]

Hi Florian

> * Cupertino Miranda via Libc-alpha:
>
>> +static void
>> +TUNABLE_CALLBACK (set_stack_hugetlb) (tunable_val_t *valp)
>> +{
>> +  enum malloc_thp_mode_t thp_mode = __malloc_thp_mode ();
>> +  /*
>> +     Only allow to change the default of this tunable if the system
>> +     does support and has either 'madvise' or 'always' mode. Otherwise
>> +     the madvise() call is wasteful.
>> +  */
>> +  switch(thp_mode)
>> +    {
>> +    case malloc_thp_mode_always:
>> +    case malloc_thp_mode_madvise:
>> +      __nptl_stack_hugetlb = (int32_t) valp->numval;
>> +      break;
>> +    default:
>> +      break;
>> +    }
>> +}
>
> I suspect that quite a few failing madvise calls are cheaper than the
> those three system calls in __malloc_thp_mode.  In addition,
> __malloc_thp_mode may fail due to future kernel changes, disabling the
> tunable by accident.
Thanks for your review. Ok, I did not check the inner workings of
malloc_thp_mode. I used it by suggestion from the RFC thread.
I will prepare a version removing it.

>
> Thanks,
> Florian