linux-kernel - Re: [PATCH 3/7] mm/hugetlb: Add page_mask for hugetlb_follow_page

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Message-ID: <ZJDMFDUZdGngQbzw@x1n>
Date:   Mon, 19 Jun 2023 17:43:48 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        James Houghton <jthoughton@...gle.com>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 3/7] mm/hugetlb: Add page_mask for
 hugetlb_follow_page_mask()

On Tue, Jun 13, 2023 at 05:53:42PM -0400, Peter Xu wrote:
> @@ -6506,6 +6507,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>  		 * because we hold the ptl lock and have verified pte_present().
>  		 */
>  		WARN_ON_ONCE(try_grab_page(page, flags));
> +		*page_mask = huge_page_mask(h);

Sorry, I was wrong this line.  It should be:

		*page_mask = ~huge_page_mask(h) >> PAGE_SHIFT;

This can be exposed if we bypass fast-gup and also specify pin npages>1.
Probably overlooked in my initial round and I'd guess fast-gup just all
succeeded there..

I'll temporarily drop the R-bs for this patch, so reviewers can have
another closer look in this one.

-- 
Peter Xu