Re: [PATCH v2 07/13] powerpc: add support for folded p4d page tables

[Christophe Leroy]

Le 26/02/2020 Ã 11:56, Mike Rapoport a ÃcritÂ:
> On Wed, Feb 26, 2020 at 10:46:13AM +0100, Christophe Leroy wrote:
> > Le 26/02/2020 Ã 10:13, Mike Rapoport a ÃcritÂ:
> > > On Tue, Feb 18, 2020 at 12:54:40PM +0200, Mike Rapoport wrote:
> > > > On Sun, Feb 16, 2020 at 11:41:07AM +0100, Christophe Leroy wrote:
> > > > > Le 16/02/2020 Ã 09:18, Mike Rapoport a ÃcritÂ:
> > > > > > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > > > > >
> > > > > > Implement primitives necessary for the 4th level folding, add walks of p4d
> > > > > > level where appropriate and replace 5level-fixup.h with pgtable-nop4d.h.
> > > > >
> > > > > I don't think it is worth adding all this additionnals walks of p4d, this
> > > > > patch could be limited to changes like:
> > > > >
> > > > > -		pud = pud_offset(pgd, gpa);
> > > > > +		pud = pud_offset(p4d_offset(pgd, gpa), gpa);
> > > > >
> > > > > The additionnal walks should be added through another patch the day powerpc
> > > > > need them.
> > > >
> > > > Ok, I'll update the patch to reduce walking the p4d.
> > >
> > > Here's what I have with more direct acceses from pgd to pud.
> >
> > I went quickly through. This looks promising.
> >
> > Do we need the walk_p4d() in arch/powerpc/mm/ptdump/hashpagetable.c ?
> > Can't we just do
> >
> > @@ -445,7 +459,7 @@ static void walk_pagetables(struct pg_state *st)
> >   		addr = KERN_VIRT_START + i * PGDIR_SIZE;
> >   		if (!pgd_none(*pgd))
> >   			/* pgd exists */
> > -			walk_pud(st, pgd, addr);
> > +			walk_pud(st, p4d_offset(pgd, addr), addr);
>
> We can do
>
> 	addr = KERN_VIRT_START + i * PGDIR_SIZE;
> 	p4d = p4d_offset(pgd, addr);
> 	if (!p4d_none(*pgd))
> 		walk_pud()
>
> But I don't think this is really essential. Again, we are trading off code
> consistency vs line count. I don't think line count is that important.

Ok.

Christophe