linux-kernel - Re: [PATCH v2 20/28] gup: Convert gup_pte

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Message-ID: <9191dcc5-375d-b894-a711-5eadebb51c5f@nvidia.com>
Date:   Mon, 10 Jan 2022 23:06:05 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>, linux-mm@...ck.org
Cc:     Christoph Hellwig <hch@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH v2 20/28] gup: Convert gup_pte_range() to use a folio

On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
> We still call try_grab_folio() once per PTE; a future patch could
> optimise to just adjust the reference count for each page within
> the folio.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>   mm/gup.c | 16 +++++++---------
>   1 file changed, 7 insertions(+), 9 deletions(-)

Still looks good.

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


thanks,
-- 
John Hubbard
NVIDIA

> 
> diff --git a/mm/gup.c b/mm/gup.c
> index c3e514172eaf..27cc097ec05d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2235,7 +2235,8 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>   	ptem = ptep = pte_offset_map(&pmd, addr);
>   	do {
>   		pte_t pte = ptep_get_lockless(ptep);
> -		struct page *head, *page;
> +		struct page *page;
> +		struct folio *folio;
>   
>   		/*
>   		 * Similar to the PMD case below, NUMA hinting must take slow
> @@ -2262,22 +2263,20 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>   		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
>   		page = pte_page(pte);
>   
> -		head = try_grab_compound_head(page, 1, flags);
> -		if (!head)
> +		folio = try_grab_folio(page, 1, flags);
> +		if (!folio)
>   			goto pte_unmap;
>   
>   		if (unlikely(page_is_secretmem(page))) {
> -			put_compound_head(head, 1, flags);
> +			gup_put_folio(folio, 1, flags);
>   			goto pte_unmap;
>   		}
>   
>   		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> -			put_compound_head(head, 1, flags);
> +			gup_put_folio(folio, 1, flags);
>   			goto pte_unmap;
>   		}
>   
> -		VM_BUG_ON_PAGE(compound_head(page) != head, page);
> -
>   		/*
>   		 * We need to make the page accessible if and only if we are
>   		 * going to access its content (the FOLL_PIN case).  Please
> @@ -2291,10 +2290,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>   				goto pte_unmap;
>   			}
>   		}
> -		SetPageReferenced(page);
> +		folio_set_referenced(folio);
>   		pages[*nr] = page;
>   		(*nr)++;
> -
>   	} while (ptep++, addr += PAGE_SIZE, addr != end);
>   
>   	ret = 1;