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

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

[pratmal]

From: Pratyush Mallick <pratmal@google.com>

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.

Signed-off-by: Pratyush Mallick <pratmal@google.com>
---
v4:
 - Added a helper function for schedule_delayed_work().
 - Updated the commit message.
 - v3: https://lore.kernel.org/linux-mm/amiPTPKfTOEpgetH@lucifer/T/#t
v3:
 - Converted page_reporting_delay_ms from a sysctl to a module parameter.
 - Dropped the max value cap (PAGE_REPORTING_DELAY_MS_MAX).
 - Documented page_reporting.page_reporting_delay_ms in Documentation/admin-guide/kernel-parameters.txt.
 - Updated code comments in mm/page_reporting.c to reflect dynamic parameterization.
 - v2: https://lore.kernel.org/linux-mm/3da27fde-25dc-4cb8-8e05-74cd26fc2f7c@kernel.org/T/#t
v2:
 - Documented page_reporting_delay_ms in Documentation/admin-guide/sysctl/vm.rst.
 - v1: https://lore.kernel.org/linux-mm/20260722192935.1646848-1-pratmal@google.com/T/#u
v1: Fixed feedback from RFC.
 - Added lower and upper cap to sysctl value.
 - Reverted the reordering on page_reporting_delay_ms.
 - Dropped the mod_delayed_work() change.
 - RFC: https://lore.kernel.org/linux-mm/20260714171456.2350037-1-pratmal@google.com/T/#u
 .../admin-guide/kernel-parameters.txt         |  6 +++++
 mm/page_reporting.c                           | 26 +++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b5493a7f8f22..364c2dce8e70 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4810,6 +4810,12 @@ Kernel parameters
 			Adjust the minimal page reporting order. The page
 			reporting is disabled when it exceeds MAX_PAGE_ORDER.
 
+	page_reporting.page_reporting_delay_ms=
+			[KNL] Free page reporting delay in milliseconds
+			Format: <unsigned integer>
+			Adjust the delay in milliseconds between free page
+			reporting intervals. Default is 2000 (2 seconds).
+
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
 			timeout > 0: seconds before rebooting
 			timeout = 0: wait forever
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 942e84b6908a..c01aa3af80f3 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -47,7 +47,11 @@ MODULE_PARM_DESC(page_reporting_order, "Set 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 {
@@ -56,6 +60,13 @@ enum {
 	PAGE_REPORTING_ACTIVE
 };
 
+/* schedule work for page reporting */
+static void page_reporting_schedule_work(struct page_reporting_dev_info *prdev)
+{
+	schedule_delayed_work(&prdev->work,
+			      msecs_to_jiffies(page_reporting_delay_ms));
+}
+
 /* request page reporting */
 static void
 __page_reporting_request(struct page_reporting_dev_info *prdev)
@@ -76,11 +87,10 @@ __page_reporting_request(struct page_reporting_dev_info *prdev)
 		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.
 	 */
-	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
+	page_reporting_schedule_work(prdev);
 }
 
 /* notify prdev of free page reporting request */
@@ -335,12 +345,12 @@ static void page_reporting_process(struct work_struct *work)
 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)
-		schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
+		page_reporting_schedule_work(prdev);
 }
 
 static DEFINE_MUTEX(page_reporting_mutex);
-- 
2.55.0.508.g3f0d502094-goog

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

[Andrew Morton]

On Fri, 31 Jul 2026 19:37:05 +0000 pratmal@google.com 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@google.com).

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);
_

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@linux-foundation.org> wrote:
>
> On Fri, 31 Jul 2026 19:37:05 +0000 pratmal@google.com 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@google.com).
>
> 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);
> _
>