linux-kernel - Re: [PATCH] Add /proc/PID/{smaps, numa

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Date:   Tue, 24 Oct 2017 01:46:34 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Fan Du <fan.du@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] Add /proc/PID/{smaps, numa_maps} support for DAX

On Tue, Oct 24, 2017 at 12:52 AM, Fan Du <fan.du@...el.com> wrote:
>
> So user could check those interface for more detailed
> information about how much DAX mappings are currently
> created.
>
> Here we use vma_is_dax method to find specific page
> struture with DAX {huge, normal}page mappings,
> vm_normal_page routine works as before without any
> impact on the existing logical where _vm_normal_page
> are called.
>
> Signed-off-by: Fan Du <fan.du@...el.com>
> ---
>  fs/proc/task_mmu.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 5589b4b..ba2e58c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -528,7 +528,11 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
>         struct page *page = NULL;
>
>         if (pte_present(*pte)) {
> -               page = vm_normal_page(vma, addr, *pte);
> +               if (!vma_is_dax(vma))
> +                       page = vm_normal_page(vma, addr, *pte);
> +               else
> +                       page = pte_page(*pte);

See usage of pte_devmap, pmd_devmap, and pud_devmap in mm/gup.c. You
need to check for that bit to know that there is a 'struct page' entry
associated with a DAX mapping.  I believe we just need to fix up and
resend his approach from last year:

    https://marc.info/?l=linux-kernel&m=148045064103357&w=2