Re: [PATCH v5 21/25] mm: Add arch hooks for saving/restoring tags

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Jun 25, 2020 at 10:04:59AM +0100, Steven Price wrote:
> On 24/06/2020 19:45, Andrew Morton wrote:
> > On Wed, 24 Jun 2020 18:52:40 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> > 
> > > From: Steven Price <steven.price@arm.com>
> > > 
> > > Arm's Memory Tagging Extension (MTE) adds some metadata (tags) to
> > > every physical page, when swapping pages out to disk it is necessary to
> > > save these tags, and later restore them when reading the pages back.
> > > 
> > > Add some hooks along with dummy implementations to enable the
> > > arch code to handle this.
> > > 
> > > Three new hooks are added to the swap code:
> > >   * arch_prepare_to_swap() and
> > >   * arch_swap_invalidate_page() / arch_swap_invalidate_area().
> > > One new hook is added to shmem:
> > >   * arch_swap_restore_tags()
> > > 
> > > ...
> > > 
> > > --- a/include/linux/pgtable.h
> > > +++ b/include/linux/pgtable.h
> > > @@ -631,6 +631,29 @@ static inline int arch_unmap_one(struct mm_struct *mm,
> > >   }
> > >   #endif
> > > +#ifndef __HAVE_ARCH_PREPARE_TO_SWAP
> > > +static inline int arch_prepare_to_swap(struct page *page)
> > > +{
> > > +	return 0;
> > > +}
> > > +#endif
> > > +
> > > +#ifndef __HAVE_ARCH_SWAP_INVALIDATE
> > > +static inline void arch_swap_invalidate_page(int type, pgoff_t offset)
> > > +{
> > > +}
> > > +
> > > +static inline void arch_swap_invalidate_area(int type)
> > > +{
> > > +}
> > > +#endif
> > > +
> > > +#ifndef __HAVE_ARCH_SWAP_RESTORE_TAGS
> > > +static inline void arch_swap_restore_tags(swp_entry_t entry, struct page *page)
> > > +{
> > > +}
> > > +#endif
> > 
> > Presumably these three __HAVE_ARCH_ macros are to be defined in asm/pgtable.h?
> 
> That would be the idea (see patch 22). However:
> 
> Catalin - you've renamed __HAVE_ARCH_SWAP_RESTORE_TAGS in patch 22, but not
> here!

This was meant to be arch_swap_restore() and __HAVE_ARCH_SWAP_RESTORE
(no tags suffix) and it was originally in include/asm-generic/pgtable.h.
With Mike's recent reworking getting rid of this file, I messed up the
conflict resolution during rebase and re-introduced this file in patch
22. I'll fix it up, it needs to be only in include/linux/pgtable.h.

-- 
Catalin