[PATCH] Document glibc.pthread.stack_hugetlb does nothing in recent kernels

[Adhemerval Zanella Netto]

On 20/01/25 17:42, Cristian Rodríguez wrote:
> Since
> c4608d1bf7c: mm: mmap: map MAP_STACK to VM_NOHUGEPAGE
> 
> All MAP_STACK allocations imply NOHUGEPAGE and the tunable does nothing.
> 
> Signed-off-by: Cristian Rodríguez <cristian@rodriguez.im>
> ---
>  manual/tunables.texi | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index 7f0246c789..468432fc57 100644
> --- a/manual/tunables.texi
> +++ b/manual/tunables.texi
> @@ -509,6 +509,10 @@ its value to @code{0} enables the use of @code{madvise} with
>  This is a memory utilization optimization, since internal glibc setup of either
>  the thread descriptor and the guard page might force the kernel to move the
>  thread stack originally backup by Huge Pages to default pages.
> +
> +This tunable has no effect on the linux kernel version 6.7

I think it was changed only for 6.8, and git describe seems to agree:

$ git describe c4608d1bf7c
v6.8-rc1-8-gc4608d1bf7c6

Besides that, the patch is ok.  Should we eventually phase out this tunable?

> +or later where MADV_NOHUGEPAGE is the default for stack mappings.
> +
>  @end deftp
>  
>  @node Hardware Capability Tunables