Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper

[Vineet Gupta]

On 06/21/2017 10:16 AM, Kirill A. Shutemov wrote:
> On Wed, Jun 21, 2017 at 08:49:03AM -0700, Vineet Gupta wrote:
> > On 06/21/2017 04:27 AM, Catalin Marinas wrote:
> > > On Wed, Jun 21, 2017 at 12:53:03PM +0300, Kirill A. Shutemov wrote:
> > > > > > > > > On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote:
> > > > > > > > > > We need an atomic way to setup pmd page table entry, avoiding races with
> > > > > > > > > > CPU setting dirty/accessed bits. This is required to implement
> > > > > > > > > > pmdp_invalidate() that doesn't loose these bits.
> > > [...]
> > > > Any chance you could help me with arm too?
> > > On arm (ARMv7 with LPAE) we don't have hardware updates of the
> > > access/dirty bits, so a generic implementation would suffice. I didn't
> > > find one in your patches, so here's an untested version:
> > >
> > > static inline pmd_t pmdp_establish(struct mm_struct *mm, unsigned long address,
> > > 				   pmd_t *pmdp, pmd_t pmd)
> > > {
> > > 	pmd_t old_pmd = *pmdp;
> > > 	set_pmd_at(mm, address, pmdp, pmd);
> > > 	return old_pmd;
> > > }
> > So it seems the discussions have settled down and pmdp_establish() can be
> > implemented in generic way as above and it will suffice if arch doesn't have
> > a special need. It would be nice to add the comment above generic version
> > that it only needs to be implemented if hardware sets the accessed/dirty
> > bits !
> >
> > Then nothing special is needed for ARC - right ?
> I will define generic version as Catalin proposed with a comment, but
> under the name generic_pmdp_establish. An arch can make use of it by
>
> #define pmdp_establish generic_pmdp_establish

Can you do that for ARC in your next posting - or want me to once you have posted 
that ?


> I don't want it to be used by default without attention from architecture
> maintainer. It can lead unnoticied breakage if THP got enabled on new
> arch.

Makes sense !

-Vineet