[PATCH v5 2/4] mm/page_reporting: Export reporting order as module parameter

[Gavin Shan <gshan@redhat.com>]

The macro PAGE_REPORTING_MIN_ORDER is defined as the page reporting
threshold. It can't be adjusted at runtime.

This introduces a variable (@page_reporting_order) to replace the
marcro (PAGE_REPORTING_MIN_ORDER). MAX_ORDER is assigned to it at
the beginning, meaning the page reporting is disabled. It will be
restored to @pageblock_order when page reporting device is registered.
It's also exported so that the page reporting order can be adjusted
at runtime.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
---
v5: Restore @page_reporting_order to @pageblock_order when device
    is registered
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 mm/page_reporting.c                             | 13 +++++++++++--
 mm/page_reporting.h                             |  5 ++---
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..566c4b9af3cd 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3566,6 +3566,12 @@
 			off: turn off poisoning (default)
 			on: turn on poisoning
 
+	page_reporting.page_reporting_order=
+			[KNL] Minimal page reporting order
+			Format: <integer>
+			Adjust the minimal page reporting order. The page
+			reporting is disabled when it exceeds (MAX_ORDER-1).
+
 	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 df9c5054e1b4..133222234f25 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -4,12 +4,17 @@
 #include <linux/page_reporting.h>
 #include <linux/gfp.h>
 #include <linux/export.h>
+#include <linux/module.h>
 #include <linux/delay.h>
 #include <linux/scatterlist.h>
 
 #include "page_reporting.h"
 #include "internal.h"
 
+unsigned int page_reporting_order = MAX_ORDER;
+module_param(page_reporting_order, uint, 0644);
+MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");
+
 #define PAGE_REPORTING_DELAY	(2 * HZ)
 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
 
@@ -229,7 +234,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 
 	/* Generate minimum watermark to be able to guarantee progress */
 	watermark = low_wmark_pages(zone) +
-		    (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
+		    (PAGE_REPORTING_CAPACITY << page_reporting_order);
 
 	/*
 	 * Cancel request if insufficient free memory or if we failed
@@ -239,7 +244,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 		return err;
 
 	/* Process each free list starting from lowest order/mt */
-	for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
+	for (order = page_reporting_order; order < MAX_ORDER; order++) {
 		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
 			/* We do not pull pages from the isolate free list */
 			if (is_migrate_isolate(mt))
@@ -324,6 +329,10 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
 		goto err_out;
 	}
 
+	/* Update the page reporting order with @pageblock_order */
+	if (page_reporting_order > pageblock_order)
+		page_reporting_order = pageblock_order;
+
 	/* initialize state and work structures */
 	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
 	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
diff --git a/mm/page_reporting.h b/mm/page_reporting.h
index 2c385dd4ddbd..c51dbc228b94 100644
--- a/mm/page_reporting.h
+++ b/mm/page_reporting.h
@@ -10,10 +10,9 @@
 #include <linux/pgtable.h>
 #include <linux/scatterlist.h>
 
-#define PAGE_REPORTING_MIN_ORDER	pageblock_order
-
 #ifdef CONFIG_PAGE_REPORTING
 DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
+extern unsigned int page_reporting_order;
 void __page_reporting_notify(void);
 
 static inline bool page_reported(struct page *page)
@@ -38,7 +37,7 @@ static inline void page_reporting_notify_free(unsigned int order)
 		return;
 
 	/* Determine if we have crossed reporting threshold */
-	if (order < PAGE_REPORTING_MIN_ORDER)
+	if (order < page_reporting_order)
 		return;
 
 	/* This will add a few cycles, but should be called infrequently */
-- 
2.23.0