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 19:54:38 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...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 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@...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,
> 

Perfectly fine :)

-- 
Cheers,

David / dhildenb