Re: [PATCH 4/5] mm: add largest_zero_folio() routine

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

On Mon, Aug 04, 2025 at 05:50:46PM +0100, Lorenzo Stoakes wrote:
> On Mon, Aug 04, 2025 at 02:13:55PM +0200, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> >
> > Add largest_zero_folio() routine so that huge_zero_folio can be
> > used directly when CONFIG_STATIC_HUGE_ZERO_FOLIO is enabled. This will
> > return ZERO_PAGE folio if CONFIG_STATIC_HUGE_ZERO_FOLIO is disabled or
> > if we failed to allocate a huge_zero_folio.
> >
> > Co-developed-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> 
> This looks good to me minus nit + comment below, so:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> 
Thanks.
> > ---
> >  include/linux/huge_mm.h | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 78ebceb61d0e..c44a6736704b 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -716,4 +716,21 @@ static inline int split_folio_to_order(struct folio *folio, int new_order)
> >  	return split_folio_to_list_to_order(folio, NULL, new_order);
> >  }
> >
> > +/*
> 
> Maybe let's make this a kernel doc comment?
Yes, I will change it in the next version :)
> 
> > + * largest_zero_folio - Get the largest zero size folio available
> > + *
> > + * This function will return huge_zero_folio if CONFIG_STATIC_HUGE_ZERO_FOLIO
> > + * is enabled. Otherwise, a ZERO_PAGE folio is returned.
> > + *
> > + * Deduce the size of the folio with folio_size instead of assuming the
> > + * folio size.
> > + */
> > +static inline struct folio *largest_zero_folio(void)
> > +{
> > +	struct folio *folio = get_static_huge_zero_folio();
> > +
> > +	if (folio)
> > +		return folio;
> > +	return page_folio(ZERO_PAGE(0));
> 
> Feels like we should have this in a wrapper function somewhere. Then again it
> seems people generally always open-code 'ZERO_PAGE(0)' anyway so maybe this is
> sort of the 'way things are done'? :P
> 
> > +}
> >  #endif /* _LINUX_HUGE_MM_H */
> > --
> > 2.49.0
> >