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@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);
_