linux-kernel - [PATCH 06/10] mm: vmscan: Have kswapd writeback pages based on dirty pages encountered, not priority

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1363525456-10448-7-git-send-email-mgorman@suse.de>
Date:	Sun, 17 Mar 2013 13:04:12 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Linux-MM <linux-mm@...ck.org>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH 06/10] mm: vmscan: Have kswapd writeback pages based on dirty pages encountered, not priority

Currently kswapd queues dirty pages for writeback if scanning at an elevated
priority but the priority kswapd scans at is not related to the number
of unqueued dirty encountered.  Since commit "mm: vmscan: Flatten kswapd
priority loop", the priority is related to the size of the LRU and the
zone watermark which is no indication as to whether kswapd should write
pages or not.

This patch tracks if an excessive number of unqueued dirty pages are being
encountered at the end of the LRU.  If so, it indicates that dirty pages
are being recycled before flusher threads can clean them and flags the
zone so that kswapd will start writing pages until the zone is balanced.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 include/linux/mmzone.h |  8 ++++++++
 mm/vmscan.c            | 29 +++++++++++++++++++++++------
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ede2749..edd6b98 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -495,6 +495,9 @@ typedef enum {
 	ZONE_CONGESTED,			/* zone has many dirty pages backed by
 					 * a congested BDI
 					 */
+	ZONE_DIRTY,			/* reclaim scanning has recently found
+					 * many dirty file pages
+					 */
 } zone_flags_t;
 
 static inline void zone_set_flag(struct zone *zone, zone_flags_t flag)
@@ -517,6 +520,11 @@ static inline int zone_is_reclaim_congested(const struct zone *zone)
 	return test_bit(ZONE_CONGESTED, &zone->flags);
 }
 
+static inline int zone_is_reclaim_dirty(const struct zone *zone)
+{
+	return test_bit(ZONE_DIRTY, &zone->flags);
+}
+
 static inline int zone_is_reclaim_locked(const struct zone *zone)
 {
 	return test_bit(ZONE_RECLAIM_LOCKED, &zone->flags);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index af3bb6f..493728b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -675,13 +675,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 				      struct zone *zone,
 				      struct scan_control *sc,
 				      enum ttu_flags ttu_flags,
-				      unsigned long *ret_nr_dirty,
+				      unsigned long *ret_nr_unqueued_dirty,
 				      unsigned long *ret_nr_writeback,
 				      bool force_reclaim)
 {
 	LIST_HEAD(ret_pages);
 	LIST_HEAD(free_pages);
 	int pgactivate = 0;
+	unsigned long nr_unqueued_dirty = 0;
 	unsigned long nr_dirty = 0;
 	unsigned long nr_congested = 0;
 	unsigned long nr_reclaimed = 0;
@@ -807,14 +808,17 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 		if (PageDirty(page)) {
 			nr_dirty++;
 
+			if (!PageWriteback(page))
+				nr_unqueued_dirty++;
+
 			/*
 			 * Only kswapd can writeback filesystem pages to
-			 * avoid risk of stack overflow but do not writeback
-			 * unless under significant pressure.
+			 * avoid risk of stack overflow but only writeback
+			 * if many dirty pages have been encountered.
 			 */
 			if (page_is_file_cache(page) &&
 					(!current_is_kswapd() ||
-					 sc->priority >= DEF_PRIORITY - 2)) {
+					 !zone_is_reclaim_dirty(zone))) {
 				/*
 				 * Immediately reclaim when written back.
 				 * Similar in principal to deactivate_page()
@@ -959,7 +963,7 @@ keep:
 	list_splice(&ret_pages, page_list);
 	count_vm_events(PGACTIVATE, pgactivate);
 	mem_cgroup_uncharge_end();
-	*ret_nr_dirty += nr_dirty;
+	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
 	*ret_nr_writeback += nr_writeback;
 	return nr_reclaimed;
 }
@@ -1372,6 +1376,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 			(nr_taken >> (DEF_PRIORITY - sc->priority)))
 		wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
 
+	/*
+	 * Similarly, if many dirty pages are encountered that are not
+	 * currently being written then flag that kswapd should start
+	 * writing back pages.
+	 */
+	if (global_reclaim(sc) && nr_dirty &&
+			nr_dirty >= (nr_taken >> (DEF_PRIORITY - sc->priority)))
+		zone_set_flag(zone, ZONE_DIRTY);
+
 	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
 		zone_idx(zone),
 		nr_scanned, nr_reclaimed,
@@ -2735,8 +2748,12 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				end_zone = i;
 				break;
 			} else {
-				/* If balanced, clear the congested flag */
+				/*
+				 * If balanced, clear the dirty and congested
+				 * flags
+				 */
 				zone_clear_flag(zone, ZONE_CONGESTED);
+				zone_clear_flag(zone, ZONE_DIRTY);
 			}
 		}
 
-- 
1.8.1.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/