linux-kernel - Re: [PATCH v2 02/10] mm/hugetlb: Don't wait for migration entry during follow page

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Message-ID: <9bf6f105-e4c6-f480-0a04-6c605981028e@nvidia.com>
Date:   Wed, 7 Dec 2022 14:03:58 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Peter Xu <peterx@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
CC:     Muchun Song <songmuchun@...edance.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        James Houghton <jthoughton@...gle.com>,
        Jann Horn <jannh@...gle.com>, Rik van Riel <riel@...riel.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Mike Kravetz" <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH v2 02/10] mm/hugetlb: Don't wait for migration entry
 during follow page

On 12/7/22 12:30, Peter Xu wrote:
> That's what the code does with !hugetlb pages, so we should logically do
> the same for hugetlb, so migration entry will also be treated as no page.

This reasoning make good sense to me. I looked again at the follow_page*()
paths and just double-checked that this is accurate, and it is.

> 
> This is probably also the last piece in follow_page code that may sleep,
> the last one should be removed in cf994dd8af27 ("mm/gup: remove
> FOLL_MIGRATION", 2022-11-16).
> 
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>   mm/hugetlb.c | 11 -----------
>   1 file changed, 11 deletions(-)

Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1088f2f41c88..c8a6673fe5b4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6232,7 +6232,6 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>   	if (WARN_ON_ONCE(flags & FOLL_PIN))
>   		return NULL;
>   
> -retry:
>   	pte = huge_pte_offset(mm, haddr, huge_page_size(h));
>   	if (!pte)
>   		return NULL;
> @@ -6255,16 +6254,6 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
>   			page = NULL;
>   			goto out;
>   		}
> -	} else {
> -		if (is_hugetlb_entry_migration(entry)) {
> -			spin_unlock(ptl);
> -			__migration_entry_wait_huge(pte, ptl);
> -			goto retry;
> -		}
> -		/*
> -		 * hwpoisoned entry is treated as no_page_table in
> -		 * follow_page_mask().
> -		 */
>   	}
>   out:
>   	spin_unlock(ptl);