Subject: Re: [PATCH v3 1/2] mm/gup: fixup for 9947ea2c1e608e32 "mm/gup: track FOLL_PIN pages"

From: John Hubbard <[email-masked]>
Date: Thu, 5 Mar 2020 14:29:59 -0800

On 3/4/20 5:06 AM, Claudio Imbrenda wrote:
> In case pin fails, we need to unpin, a simple put_page will not be enough
> 
> fixup for commit 9947ea2c1e608e32 ("mm/gup: track FOLL_PIN pages")
> 
> it can be simply squashed in
> 
> Signed-off-by: Claudio Imbrenda <[email-masked]>
> ---

Although it won't show up anywhere, in case this helps Andrew sort out what
has been looked at, you can add: 

    Reviewed-by: John Hubbard <[email-masked]>

thanks,
-- 
John Hubbard
NVIDIA

>  mm/gup.c | 46 +++++++++++++++++++++++-----------------------
>  1 file changed, 23 insertions(+), 23 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index f589299b0d4a..81a95fbe9901 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -116,6 +116,28 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page,
>  	return NULL;
>  }
>  
> +static void put_compound_head(struct page *page, int refs, unsigned int flags)
> +{
> +	if (flags & FOLL_PIN) {
> +		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
> +				    refs);
> +
> +		if (hpage_pincount_available(page))
> +			hpage_pincount_sub(page, refs);
> +		else
> +			refs *= GUP_PIN_COUNTING_BIAS;
> +	}
> +
> +	VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
> +	/*
> +	 * Calling put_page() for each ref is unnecessarily slow. Only the last
> +	 * ref needs a put_page().
> +	 */
> +	if (refs > 1)
> +		page_ref_sub(page, refs - 1);
> +	put_page(page);
> +}
> +
>  /**
>   * try_grab_page() - elevate a page's refcount by a flag-dependent amount
>   *
> @@ -2134,7 +2156,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
>  			goto pte_unmap;
>  
>  		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
> -			put_page(head);
> +			put_compound_head(head, 1, flags);
>  			goto pte_unmap;
>  		}
>  
> @@ -2267,28 +2289,6 @@ static int record_subpages(struct page *page, unsigned long addr,
>  	return nr;
>  }
>  
> -static void put_compound_head(struct page *page, int refs, unsigned int flags)
> -{
> -	if (flags & FOLL_PIN) {
> -		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
> -				    refs);
> -
> -		if (hpage_pincount_available(page))
> -			hpage_pincount_sub(page, refs);
> -		else
> -			refs *= GUP_PIN_COUNTING_BIAS;
> -	}
> -
> -	VM_BUG_ON_PAGE(page_ref_count(page) < refs, page);
> -	/*
> -	 * Calling put_page() for each ref is unnecessarily slow. Only the last
> -	 * ref needs a put_page().
> -	 */
> -	if (refs > 1)
> -		page_ref_sub(page, refs - 1);
> -	put_page(page);
> -}
> -
>  #ifdef CONFIG_ARCH_HAS_HUGEPD
>  static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
>  				      unsigned long sz)
>