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

[Mike Rapoport <rppt@kernel.org>]

On Thu, Jul 16, 2026 at 03:38:59PM +0800, Muchun Song wrote:
> 
> 
> 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@bytedance.com>
> > > 
> > > 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

Sounds good :) 
 
> > 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.

-- 
Sincerely yours,
Mike.