Re: [PATCH 03/17] mm/sparse-vmemmap: introduce folio-oriented vmemmap optimization macros

[Muchun Song]

On 2026/7/15 13:08, Mike Rapoport wrote:
> > Introduce macros for those folio-oriented properties and use them to
> > replace the tail-based names in the HVO paths. This makes the code read
> > in terms of folio semantics instead of an implementation detail and
> > better matches other folio-based users such as DAX.
> >
> > No functional change intended.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index bacd89572c5c..ea884245f499 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -107,13 +107,15 @@
> >   	 is_power_of_2(sizeof(struct page)) ? \
> >   	 MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
> >   
> > -/*
> > - * vmemmap optimization (like HVO) is only possible for page orders that fill
> > - * two or more pages with struct pages.
> > - */
> > -#define VMEMMAP_TAIL_MIN_ORDER (ilog2(2 * PAGE_SIZE / sizeof(struct page)))
> > -#define __NR_VMEMMAP_TAILS (MAX_FOLIO_ORDER - VMEMMAP_TAIL_MIN_ORDER + 1)
> > -#define NR_VMEMMAP_TAILS (__NR_VMEMMAP_TAILS > 0 ? __NR_VMEMMAP_TAILS : 0)
> > +/* The number of vmemmap pages required by a vmemmap-optimized folio. */
> > +#define OPTIMIZED_FOLIO_VMEMMAP_PAGES		1
> > +#define OPTIMIZED_FOLIO_VMEMMAP_SIZE		(OPTIMIZED_FOLIO_VMEMMAP_PAGES * PAGE_SIZE)
> > +#define OPTIMIZED_FOLIO_VMEMMAP_NR_STRUCT_PAGES	(OPTIMIZED_FOLIO_VMEMMAP_SIZE / sizeof(struct page))
> > +#define OPTIMIZABLE_FOLIO_MIN_ORDER		(ilog2(OPTIMIZED_FOLIO_VMEMMAP_NR_STRUCT_PAGES) + 1)
> > +
> > +#define __NR_OPTIMIZABLE_FOLIO_ORDERS		(MAX_FOLIO_ORDER - OPTIMIZABLE_FOLIO_MIN_ORDER + 1)
> > +#define NR_OPTIMIZABLE_FOLIO_ORDERS		\
> > +	(__NR_OPTIMIZABLE_FOLIO_ORDERS > 0 ? __NR_OPTIMIZABLE_FOLIO_ORDERS : 0)
> I can't say I like the new names, they read like some folio optimization
> rather than vmemmap optimization.
>
> I think they should be namespaced with VMEMMAP_ or even
> VMEMMAP_OPTIMIZATION_ (or VMEMMAP_OPT_) and should not mention folio.

If you're okay with it, I'll update those macros to:

VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES
VMEMMAP_OPTIMIZATION_MIN_ORDER
VMEMMAP_OPTIMIZATION_NR_ORDERS

> I'd also drop intermediate defines OPTIMIZED_FOLIO_VMEMMAP_PAGES and
> OPTIMIZED_FOLIO_VMEMMAP_SIZE and use 1 and PAGE_SIZE directly.

OK. I'll not introduce OPTIMIZED_FOLIO_VMEMMAP_PAGES and
OPTIMIZED_FOLIO_VMEMMAP_SIZE

Muchun,
Thanks.