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

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Message-ID: <aYcTEFK3D3LDVUPR@fedora>
Date: Sat, 7 Feb 2026 02:25:20 -0800
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	akpm@...ux-foundation.org,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v4 1/4] mm: Add address apis for ptdescs

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@...el.com>
> > Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
> > ---
> >  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.