Re: [RFC v2 0/2] add THP_HUGE_ZERO_PAGE_ALWAYS config option

["Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>]

Hi David,

> >   config ARCH_WANTS_THP_SWAP
> >          def_bool n
> > -config ARCH_WANTS_THP_ZERO_PAGE_ALWAYS
> > +config ARCH_WANTS_HUGE_ZERO_PAGE_ALWAYS
> >          def_bool n
> > +config HUGE_ZERO_PAGE_ALWAYS
> 
> Likely something like
> 
> PMD_ZERO_PAGE
> 
> Will be a lot clearer.

Sounds much better :)

> 
> > +       def_bool y> +       depends on HUGETLB_PAGE &&
> ARCH_WANTS_HUGE_ZERO_PAGE_ALWAYS
> 
> I suspect it should then also be independent of HUGETLB_PAGE?

You are right. So we don't depend on any of these features.

> 
> > +       help
> > +         Typically huge_zero_folio, which is a huge page of zeroes, is allocated
> > +         on demand and deallocated when not in use. This option will always
> > +         allocate huge_zero_folio for zeroing and it is never deallocated.
> > +         Not suitable for memory constrained systems.
> 
> I assume that code then has to live in mm/memory.c ?

Hmm, then huge_zero_folio should have always been in mm/memory.c to
begin with?

I assume probably this was placed in mm/huge_memory.c because the users
of this huge_zero_folio has been a part of mm/huge_memory.c?

So IIUC your comment, we should move the huge_zero_page_init() in the
first patch to mm/memory.c and the existing shrinker code can be a part
where they already are?

--
Pankaj