Re: [PATCH v2 3/8] mm/hugetlb: Add page_mask for hugetlb_follow_page_mask()

[David Hildenbrand <david@xxxxxxxxxx>]

On 20.06.23 18:28, Peter Xu wrote:
> On Tue, Jun 20, 2023 at 05:23:09PM +0200, David Hildenbrand wrote:
> > On 20.06.23 01:10, Peter Xu wrote:
> > > follow_page() doesn't need it, but we'll start to need it when unifying gup
> > > for hugetlb.
> > >
> > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> > > ---
> > >    include/linux/hugetlb.h | 8 +++++---
> > >    mm/gup.c                | 3 ++-
> > >    mm/hugetlb.c            | 5 ++++-
> > >    3 files changed, 11 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > > index beb7c63d2871..2e2d89e79d6c 100644
> > > --- a/include/linux/hugetlb.h
> > > +++ b/include/linux/hugetlb.h
> > > @@ -131,7 +131,8 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
> > >    int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *,
> > >    			    struct vm_area_struct *, struct vm_area_struct *);
> > >    struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> > > -				unsigned long address, unsigned int flags);
> > > +				      unsigned long address, unsigned int flags,
> > > +				      unsigned int *page_mask);
> > >    long follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *,
> > >    			 struct page **, unsigned long *, unsigned long *,
> > >    			 long, unsigned int, int *);
> > > @@ -297,8 +298,9 @@ static inline void adjust_range_if_pmd_sharing_possible(
> > >    {
> > >    }
> > > -static inline struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> > > -				unsigned long address, unsigned int flags)
> > > +static inline struct page *hugetlb_follow_page_mask(
> > > +    struct vm_area_struct *vma, unsigned long address, unsigned int flags,
> > > +    unsigned int *page_mask)
> > >    {
> > >    	BUILD_BUG(); /* should never be compiled in if !CONFIG_HUGETLB_PAGE*/
> > >    }
> > > diff --git a/mm/gup.c b/mm/gup.c
> > > index abcd841d94b7..9fc9271cba8d 100644
> > > --- a/mm/gup.c
> > > +++ b/mm/gup.c
> > > @@ -780,7 +780,8 @@ static struct page *follow_page_mask(struct vm_area_struct *vma,
> > >    	 * Ordinary GUP uses follow_hugetlb_page for hugetlb processing.
> > >    	 */
> > >    	if (is_vm_hugetlb_page(vma))
> > > -		return hugetlb_follow_page_mask(vma, address, flags);
> > > +		return hugetlb_follow_page_mask(vma, address, flags,
> > > +						&ctx->page_mask);
> > >    	pgd = pgd_offset(mm, address);
> > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > > index 9a6918c4250a..fbf6a09c0ec4 100644
> > > --- a/mm/hugetlb.c
> > > +++ b/mm/hugetlb.c
> > > @@ -6454,7 +6454,8 @@ static inline bool __follow_hugetlb_must_fault(struct vm_area_struct *vma,
> > >    }
> > >    struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> > > -				unsigned long address, unsigned int flags)
> > > +				      unsigned long address, unsigned int flags,
> > > +				      unsigned int *page_mask)
> > >    {
> > >    	struct hstate *h = hstate_vma(vma);
> > >    	struct mm_struct *mm = vma->vm_mm;
> > > @@ -6499,6 +6500,8 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> > >    			page = NULL;
> > >    			goto out;
> > >    		}
> > > +
> > > +		*page_mask = ~huge_page_mask(h) >> PAGE_SHIFT;
> >
> > As discussed, can be simplified. But can be done on top (or not at all, but
> > it is confusing code).
>
> Since we decided to make this prettier..  At last I decided to go with this:
>
> 		*page_mask = (1U << huge_page_order(h)) - 1;
>
> The previous suggestion of PHYS_PFN() will do two shifts over PAGE_SIZE
> (the other one in huge_page_size()) which might be unnecessary, also, PHYS_
> can be slightly misleading too as prefix.
>
> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
>
> I'll take this with above change, please shoot if not applicable.  Thanks,

Perfectly fine :)

--
Cheers,

David / dhildenb