linux-kernel - Re: [PATCH] mm: dax: add comment for PFN

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Date:   Thu, 27 Sep 2018 14:08:51 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     yang.shi@...ux.alibaba.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: dax: add comment for PFN_SPECIAL

On Thu, Sep 27, 2018 at 12:39 PM <yang.shi@...ux.alibaba.com> wrote:
>
> The comment for PFN_SPECIAL is missed in pfn_t.h. Add comment to get
> consistent with other pfn flags.
>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
>  include/linux/pfn_t.h | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/pfn_t.h b/include/linux/pfn_t.h
> index 21713dc..d2e5dd4 100644
> --- a/include/linux/pfn_t.h
> +++ b/include/linux/pfn_t.h
> @@ -9,6 +9,7 @@
>   * PFN_SG_LAST - pfn references a page and is the last scatterlist entry
>   * PFN_DEV - pfn is not covered by system memmap by default
>   * PFN_MAP - pfn has a dynamic page mapping established by a device driver
> + * PFN_SPECIAL - indicates that _PAGE_SPECIAL should be used for DAX ptes

That's not quite accurate, I would change this to:

PFN_SPECIAL - for CONFIG_FS_DAX_LIMITED builds to allow XIP, but not
get_user_pages.