Re: [PATCH v4] mm/page_reporting: Add page_reporting_delay_ms module parameter

[Pratyush Mallick]

Sorry I forgot to update it in v4. Resolution looks good to me.
Thanks Again!

Regards,
Pratyush


On Fri, Jul 31, 2026 at 2:34 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, 31 Jul 2026 19:37:05 +0000 pratmal@xxxxxxxxxx wrote:
>
> > Free page reporting currently hardcodes a 2-second interval between
> > reports. This rigid delay cannot accommodate diverse guest workloads.
> >
> > This patch introduces a module parameter, page_reporting_delay_ms
> > (default: 2000), allowing users to tune the reporting rate:
> >  - Lower values enable aggressive memory reclamation by returning unused
> >    pages to the host immediately.
> >  - Higher values help batch pages during spiky allocation/free churn,
> >    reducing hypercalls and nested page fault overheads.
> >
> > Setting the delay to 0 is safe and execution is strictly gated by:
> >  - reporting is only triggered by high-order page frees.
> >  - expensive hypercalls are bounded by a slot capacity watermark check
> >    before proceeding.
>
> This conflcits with the just-upstreamed 0b45f6927a1
> ("mm/page_reporting: use system_freezable_wq to fix UAF during
> suspend")
> (https://lore.kernel.org/20260721005603.1710551-1-linkl@xxxxxxxxxx).
>
> Please review my resolution:
>
> --- a/mm/page_reporting.c~mm-page_reporting-add-page_reporting_delay_ms-module-parameter
> +++ a/mm/page_reporting.c
> @@ -48,7 +48,11 @@ MODULE_PARM_DESC(page_reporting_order, "
>   */
>  EXPORT_SYMBOL_GPL(page_reporting_order);
>
> -#define PAGE_REPORTING_DELAY   (2 * HZ)
> +static unsigned int page_reporting_delay_ms = 2 * MSEC_PER_SEC;
> +module_param(page_reporting_delay_ms, uint, 0644);
> +MODULE_PARM_DESC(page_reporting_delay_ms,
> +                "Set page reporting delay in milliseconds");
> +
>  static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
>
>  enum {
> @@ -57,6 +61,13 @@ enum {
>         PAGE_REPORTING_ACTIVE
>  };
>
> +/* schedule work for page reporting */
> +static void page_reporting_schedule_work(struct page_reporting_dev_info *prdev)
> +{
> +       queue_delayed_work(system_freezable_wq, &prdev->work,
> +                             msecs_to_jiffies(page_reporting_delay_ms));
> +}
> +
>  /* request page reporting */
>  static void
>  __page_reporting_request(struct page_reporting_dev_info *prdev)
> @@ -77,12 +88,10 @@ __page_reporting_request(struct page_rep
>                 return;
>
>         /*
> -        * Delay the start of work to allow a sizable queue to build. For
> -        * now we are limiting this to running no more than once every
> -        * couple of seconds.
> +        * Delay the start of work to allow a sizable queue to build.
> +        * We limit this based on page_reporting_delay_ms.
>          */
> -       queue_delayed_work(system_freezable_wq, &prdev->work,
> -                          PAGE_REPORTING_DELAY);
> +       page_reporting_schedule_work(prdev);
>  }
>
>  /* notify prdev of free page reporting request */
> @@ -337,13 +346,12 @@ static void page_reporting_process(struc
>  err_out:
>         /*
>          * If the state has reverted back to requested then there may be
> -        * additional pages to be processed. We will defer for 2s to allow
> -        * more pages to accumulate.
> +        * additional pages to be processed. We will defer by
> +        * page_reporting_delay_ms to allow more pages to accumulate.
>          */
>         state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
>         if (state == PAGE_REPORTING_REQUESTED)
> -               queue_delayed_work(system_freezable_wq, &prdev->work,
> -                                  PAGE_REPORTING_DELAY);
> +               page_reporting_schedule_work(prdev);
>  }
>
>  static DEFINE_MUTEX(page_reporting_mutex);
> _
>