[PATCH RFC v3 14/19] mm: page_reporting: add flush parameter with page budget

["Michael S. Tsirkin" <mst@redhat.com>]

Add a write-only module parameter 'flush' that triggers immediate
page reporting.  The value specifies approximately how many pages
(at page_reporting_order) to report.  The flush loops through
reporting cycles, each processing up to PAGE_REPORTING_CAPACITY
pages, until the budget is exhausted, all pages are reported, or
a signal is pending.

This is helpful when there is a lot of memory freed quickly,
and a single cycle may not process all free pages due to
internal budget limits.

  echo 512 > /sys/module/page_reporting/parameters/flush

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: Claude:claude-opus-4-6
---
 mm/page_reporting.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 6177d2413743..c09a8ac754dc 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -354,6 +354,48 @@ static void page_reporting_process(struct work_struct *work)
 static DEFINE_MUTEX(page_reporting_mutex);
 DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
 
+static int page_reporting_flush_set(const char *val,
+				    const struct kernel_param *kp)
+{
+	struct page_reporting_dev_info *prdev;
+	unsigned int budget;
+	int err;
+
+	err = kstrtouint(val, 0, &budget);
+	if (err)
+		return err;
+	if (!budget)
+		return 0;
+
+	mutex_lock(&page_reporting_mutex);
+	prdev = rcu_dereference_protected(pr_dev_info,
+				lockdep_is_held(&page_reporting_mutex));
+	if (prdev) {
+		unsigned int reported;
+
+		for (reported = 0; reported < budget;
+		     reported += PAGE_REPORTING_CAPACITY) {
+			flush_delayed_work(&prdev->work);
+			__page_reporting_request(prdev);
+			flush_delayed_work(&prdev->work);
+			if (atomic_read(&prdev->state) == PAGE_REPORTING_IDLE)
+				break;
+			if (signal_pending(current))
+				break;
+		}
+	}
+	mutex_unlock(&page_reporting_mutex);
+	return 0;
+}
+
+static const struct kernel_param_ops flush_ops = {
+	.set = page_reporting_flush_set,
+	.get = param_get_uint,
+};
+static unsigned int page_reporting_flush;
+module_param_cb(flush, &flush_ops, &page_reporting_flush, 0200);
+MODULE_PARM_DESC(flush, "Report up to N pages at page_reporting_order");
+
 int page_reporting_register(struct page_reporting_dev_info *prdev)
 {
 	int err = 0;
-- 
MST