[RFC PATCH 1/4] mm: reduce the impaction of page reporing worker

[liliangleo]

When scaning the free list, 'page_reporting_cycle' may hold the
zone->lock for a long time when there are no reported page in the
free list. Setting PAGE_REPORTING_MIN_ORDER to a lower oder will
make this issue worse.

Two ways were used to reduce the impact:
   1. Release zone lock periodicly
   2. Yield cpu voluntarily if needed.

Signed-off-by: liliangleo <liliangleo@xxxxxxxxxxxxxx>
---
 mm/page_reporting.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index 3bbd471cfc81..3a7084e508e1 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -6,11 +6,14 @@
 #include <linux/export.h>
 #include <linux/delay.h>
 #include <linux/scatterlist.h>
+#include <linux/sched.h>
 
 #include "page_reporting.h"
 #include "internal.h"
 
 #define PAGE_REPORTING_DELAY	(2 * HZ)
+#define MAX_SCAN_NUM 1024
+
 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
 
 enum {
@@ -115,7 +118,7 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 	unsigned int page_len = PAGE_SIZE << order;
 	struct page *page, *next;
 	long budget;
-	int err = 0;
+	int err = 0, scan_cnt = 0;
 
 	/*
 	 * Perform early check, if free area is empty there is
@@ -145,8 +148,14 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 	/* loop through free list adding unreported pages to sg list */
 	list_for_each_entry_safe(page, next, list, lru) {
 		/* We are going to skip over the reported pages. */
-		if (PageReported(page))
+		if (PageReported(page)) {
+			if (++scan_cnt >= MAX_SCAN_NUM) {
+				err = scan_cnt;
+				break;
+			}
 			continue;
+		}
+
 
 		/*
 		 * If we fully consumed our budget then update our
@@ -219,6 +228,26 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 	return err;
 }
 
+static int
+reporting_order_type(struct page_reporting_dev_info *prdev, struct zone *zone,
+		     unsigned int order, unsigned int mt,
+		     struct scatterlist *sgl, unsigned int *offset)
+{
+	int ret = 0;
+	unsigned long total = 0;
+
+	might_sleep();
+	do {
+		cond_resched();
+		ret = page_reporting_cycle(prdev, zone, order, mt,
+					   sgl, offset);
+		if (ret > 0)
+			total += ret;
+	} while (ret > 0 && total < zone->free_area[order].nr_free);
+
+	return ret;
+}
+
 static int
 page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 			    struct scatterlist *sgl, struct zone *zone)
@@ -245,7 +274,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 			if (is_migrate_isolate(mt))
 				continue;
 
-			err = page_reporting_cycle(prdev, zone, order, mt,
+			err = reporting_order_type(prdev, zone, order, mt,
 						   sgl, &offset);
 			if (err)
 				return err;
-- 
2.14.1