linux-kernel - Re: [PATCH v3] mm/page_owner.c: add llseek for page

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Date:   Sat, 30 Jul 2022 07:58:49 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Kassey Li <quic_yingangl@...cinc.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, vbabka@...nel.org,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v3] mm/page_owner.c: add llseek for page_owner

On Fri, Jul 29, 2022 at 6:19 AM Kassey Li <quic_yingangl@...cinc.com> wrote:
>
> There is usage to dump a given cma region page_owner
> instead of all page's.
>
> This change allows to specify a ppos as start_pfn
> by fseek.
>
> Any invalid ppos will be skipped, so it did not
> broken the origin dump feature.
>

I think a Suggested-by tag needs to be added.


> Signed-off-by: Kassey Li <quic_yingangl@...cinc.com>
> ---
>  mm/page_owner.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index e4c6f3f1695b..231b1877af99 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -497,8 +497,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>                 return -EINVAL;
>
>         page = NULL;
> -       pfn = min_low_pfn + *ppos;
>
> +       pfn = *ppos;
>         /* Find a valid PFN or the start of a MAX_ORDER_NR_PAGES area */
>         while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
>                 pfn++;
> @@ -561,7 +561,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>                         continue;
>
>                 /* Record the next PFN to read in the file offset */
> -               *ppos = (pfn - min_low_pfn) + 1;
> +               *ppos = pfn + 1;
>
>                 return print_page_owner(buf, count, pfn, page,
>                                 page_owner, handle);
> @@ -570,6 +570,21 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>         return 0;
>  }
>
> +static loff_t llseek_page_owner(struct file *file, loff_t offset, int whence)
> +{
> +       loff_t retval = 0;
> +       switch (whence) {
> +               case SEEK_CUR:
> +               case SEEK_SET:
> +                       file->f_pos = offset;
> +                       break;
> +               default:
> +                       retval = -ENXIO;
> +       }
> +
> +       return retval;
> +}
> +
>  static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone)
>  {
>         unsigned long pfn = zone->zone_start_pfn;
> @@ -660,6 +675,7 @@ static void init_early_allocated_pages(void)
>
>  static const struct file_operations proc_page_owner_operations = {
>         .read           = read_page_owner,
> +       .llseek         = llseek_page_owner,
>  };
>
>  static int __init pageowner_init(void)
> --
> 2.17.1
>
>