[RFC v2 PATCH 2/4] mm: Add batch size for free page reporting

[Liang Li]

Use the page order as the only threshold for page reporting
is not flexible and has some flaws.
When the system's memory becomes very fragmented, there will be a
lot of low order free pages but very few high order pages, limit
the mini order as pageblock_order will prevent most of free pages
from being reclaimed by host for the case of page reclmain through
the virtio-balllon driver.
Scan a long free list is not cheap, it's better to wake up the
page reporting worker when there are more pages, wake it up for a
sigle page may not worth.
This patch add a batch size as another threshold to control the
waking up of reporting worker.

Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Liang Li <liliang324@xxxxxxxxx>
---
 mm/page_reporting.c |  2 ++
 mm/page_reporting.h | 12 ++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 0b22db94ce2a..2f8e3d032fab 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -14,6 +14,8 @@
 #define PAGE_REPORTING_DELAY	(2 * HZ)
 #define MAX_SCAN_NUM 1024
 
+unsigned long page_report_batch_size  __read_mostly = 4 * 1024 * 1024UL;
+
 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
 
 enum {
diff --git a/mm/page_reporting.h b/mm/page_reporting.h
index 2c385dd4ddbd..b8fb3bbb345f 100644
--- a/mm/page_reporting.h
+++ b/mm/page_reporting.h
@@ -12,6 +12,8 @@
 
 #define PAGE_REPORTING_MIN_ORDER	pageblock_order
 
+extern unsigned long page_report_batch_size;
+
 #ifdef CONFIG_PAGE_REPORTING
 DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
 void __page_reporting_notify(void);
@@ -33,6 +35,8 @@ static inline bool page_reported(struct page *page)
  */
 static inline void page_reporting_notify_free(unsigned int order)
 {
+	static long batch_size;
+
 	/* Called from hot path in __free_one_page() */
 	if (!static_branch_unlikely(&page_reporting_enabled))
 		return;
@@ -41,8 +45,12 @@ static inline void page_reporting_notify_free(unsigned int order)
 	if (order < PAGE_REPORTING_MIN_ORDER)
 		return;
 
-	/* This will add a few cycles, but should be called infrequently */
-	__page_reporting_notify();
+	batch_size += (1 << order) << PAGE_SHIFT;
+	if (batch_size >= page_report_batch_size) {
+		batch_size = 0;
+		/* This add a few cycles, but should be called infrequently */
+		__page_reporting_notify();
+	}
 }
 #else /* CONFIG_PAGE_REPORTING */
 #define page_reported(_page)	false
-- 
2.18.2