Re: [PATCH v4 1/4] mm: Add address apis for ptdescs

[Vishal Moola (Oracle)]

On Sat, Feb 07, 2026 at 09:45:22AM +0200, Mike Rapoport wrote:
> Hi Vishal,
> 
> On Wed, Feb 04, 2026 at 05:35:24PM -0800, Vishal Moola (Oracle) wrote:
> > Architectures frequently only care about the address associated with a
> > page table. The current ptdesc api forced callers to acquire a ptdesc to
> > use them. Add more apis to abstract ptdescs away from architectures that
> > don't need the descriptor.
> > 
> > This patch adds pgtable_alloc() and pgtable_free() to operate on the
> > underlying addresses associated with page table descriptors, similar to
> > get_free_pages() and free_pages(). The allocations will be zeroed since
> > theres no reason to want a page table with stale data.
> > 
> > Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
> > Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
> > ---
> >  include/linux/mm.h |  4 ++++
> >  mm/memory.c        | 34 ++++++++++++++++++++++++++++++++++
> >  2 files changed, 38 insertions(+)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index f8a8fd47399c..3f3000567823 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -3419,6 +3419,10 @@ static inline void __pagetable_free(struct ptdesc *pt)
> >  	__free_pages(page, compound_order(page));
> >  }
> >  
> > +unsigned long pgtable_alloc_addr_noprof(gfp_t gfp, unsigned int order);
> 
> Why not void *?
> I don't think it should follow ancient get_zeroed_page() and force all
> callers to do the casting when they are expecting a pointer anyway.

Agreed, I'll change that in the next version.

I had misread an s390 function that expects an (unsigned long *) and assumed
some callers might want the unsigned long, thinking we'd have to cast anyway.
After taking a closer look I see now that every single caller actually
expects a pointer.