[PATCH 7/7] mm: vmscan: Immediately reclaim end-of-LRU dirty pages when writeback completes

[Mel Gorman <mgorman@suse.de>]

When direct reclaim encounters a dirty page, it gets recycled around
the LRU for another cycle. This patch marks the page PageReclaim
similar to deactivate_page() so that the page gets reclaimed almost
immediately after the page gets cleaned. This is to avoid reclaiming
clean pages that are younger than a dirty page encountered at the
end of the LRU that might have been something like a use-once page.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <jweiner@redhat.com>
---
 include/linux/mmzone.h |    2 +-
 mm/vmscan.c            |   10 +++++++++-
 mm/vmstat.c            |    2 +-
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b70a0c0..c9c5797 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -100,7 +100,7 @@ enum zone_stat_item {
 	NR_UNSTABLE_NFS,	/* NFS unstable pages */
 	NR_BOUNCE,
 	NR_VMSCAN_WRITE,
-	NR_VMSCAN_WRITE_SKIP,
+	NR_VMSCAN_IMMEDIATE,	/* Prioritise for reclaim when writeback ends */
 	NR_WRITEBACK_TEMP,	/* Writeback using temporary buffers */
 	NR_ISOLATED_ANON,	/* Temporary isolated pages from anon lru */
 	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b0437f2..33882a3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -826,7 +826,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 			 */
 			if (page_is_file_cache(page) &&
 					(!current_is_kswapd() || priority >= DEF_PRIORITY - 2)) {
-				inc_zone_page_state(page, NR_VMSCAN_WRITE_SKIP);
+				/*
+				 * Immediately reclaim when written back.
+				 * Similar in principal to deactivate_page()
+				 * except we already have the page isolated
+				 * and know it's dirty
+				 */
+				inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
+				SetPageReclaim(page);
+
 				goto keep_locked;
 			}
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index fd109f3..471b20b 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -702,7 +702,7 @@ const char * const vmstat_text[] = {
 	"nr_unstable",
 	"nr_bounce",
 	"nr_vmscan_write",
-	"nr_vmscan_write_skip",
+	"nr_vmscan_immediate_reclaim",
 	"nr_writeback_temp",
 	"nr_isolated_anon",
 	"nr_isolated_file",
-- 
1.7.3.4

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