linux-kernel - Re: [PATCH 1/6] mm/gup: perform check_dax_vmas only when FS

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Message-ID: <be8546cc-bad3-d47e-dae7-0daca69c699c@nvidia.com>
Date:   Wed, 2 Dec 2020 23:59:30 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <akpm@...ux-foundation.org>, <vbabka@...e.cz>, <mhocko@...e.com>,
        <david@...hat.com>, <osalvador@...e.de>,
        <dan.j.williams@...el.com>, <sashal@...nel.org>,
        <tyhicks@...ux.microsoft.com>, <iamjoonsoo.kim@....com>,
        <mike.kravetz@...cle.com>, <rostedt@...dmis.org>,
        <mingo@...hat.com>, <jgg@...pe.ca>, <peterz@...radead.org>,
        <mgorman@...e.de>, <willy@...radead.org>, <rientjes@...gle.com>
Subject: Re: [PATCH 1/6] mm/gup: perform check_dax_vmas only when FS_DAX is
 enabled

On 12/1/20 9:23 PM, Pavel Tatashin wrote:
> There is no need to check_dax_vmas() and run through the npage loop of
> pinned pages if FS_DAX is not enabled.
> 
> Add a stub check_dax_vmas() function for no-FS_DAX case.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> ---
>   mm/gup.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 98eb8e6d2609..cdb8b9eeb016 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1568,6 +1568,7 @@ struct page *get_dump_page(unsigned long addr)
>   #endif /* CONFIG_ELF_CORE */
>   
>   #if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
> +#ifdef CONFIG_FS_DAX
>   static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>   {
>   	long i;
> @@ -1586,6 +1587,12 @@ static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
>   	}
>   	return false;
>   }
> +#else
> +static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
> +{
> +	return false;
> +}
> +#endif
>   
>   #ifdef CONFIG_CMA
>   static long check_and_migrate_cma_pages(struct mm_struct *mm,
> 

Looks obviously correct, and the follow-up simplication is very nice.

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

thanks,
-- 
John Hubbard
NVIDIA