linux-kernel - Re: [PATCH v2 3/8] mm/hugetlb: Add page_mask for hugetlb_follow_page

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Date:   Tue, 20 Jun 2023 12:28:26 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Rapoport <rppt@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        James Houghton <jthoughton@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 3/8] mm/hugetlb: Add page_mask for
 hugetlb_follow_page_mask()

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@...hat.com>
> > ---
> >   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@...hat.com>

I'll take this with above change, please shoot if not applicable.  Thanks,

-- 
Peter Xu