linux-kernel - Re: [PATCH v3] hugetlb: simplify hugetlb handling in follow_page

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Date:   Mon, 19 Sep 2022 09:50:12 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-ia64@...r.kernel.org
Cc:     Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Michael Ellerman <mpe@...erman.id.au>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] hugetlb: simplify hugetlb handling in follow_page_mask

On 19.09.22 04:13, Mike Kravetz wrote:
> During discussions of this series [1], it was suggested that hugetlb
> handling code in follow_page_mask could be simplified.  At the beginning
> of follow_page_mask, there currently is a call to follow_huge_addr which
> 'may' handle hugetlb pages.  ia64 is the only architecture which provides
> a follow_huge_addr routine that does not return error.  Instead, at each
> level of the page table a check is made for a hugetlb entry.  If a hugetlb
> entry is found, a call to a routine associated with that entry is made.
> 
> Currently, there are two checks for hugetlb entries at each page table
> level.  The first check is of the form:
>          if (p?d_huge())
>                  page = follow_huge_p?d();
> the second check is of the form:
>          if (is_hugepd())
>                  page = follow_huge_pd().
> 
> We can replace these checks, as well as the special handling routines
> such as follow_huge_p?d() and follow_huge_pd() with a single routine to
> handle hugetlb vmas.
> 
> A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the
> beginning of follow_page_mask.  hugetlb_follow_page_mask will use the
> existing routine huge_pte_offset to walk page tables looking for hugetlb
> entries.  huge_pte_offset can be overwritten by architectures, and already
> handles special cases such as hugepd entries.
> 
> [1] https://lore.kernel.org/linux-mm/cover.1661240170.git.baolin.wang@linux.alibaba.com/
> 
> Suggested-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb