[RFC][PATCH -mm -v2 4/4] mm,vmscan: evict inactive file pages first

[Rik van Riel <riel@redhat.com>]

When a lot of streaming file IO is happening, it makes sense to
evict just the inactive file pages and leave the other LRU lists
alone.

Likewise, when driving a cgroup hierarchy into its hard limit,
or over its soft limit, it makes sense to pick a child cgroup
that has lots of inactive file pages, and evict those first.

Being over its soft limit is considered a stronger preference
than just having a lot of inactive file pages, so a well behaved
cgroup is allowed to keep its file cache when there is a "badly
behaving" one in the same hierarchy.

Signed-off-by: Rik van Riel <riel@redhat.com>
---
 mm/vmscan.c |   37 +++++++++++++++++++++++++++++++++----
 1 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 769fdcd..2884b4f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1576,6 +1576,19 @@ static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
 		return inactive_anon_is_low(lruvec);
 }
 
+/* If this lruvec has lots of inactive file pages, reclaim those only. */
+static bool reclaim_file_only(struct lruvec *lruvec, struct scan_control *sc,
+			      unsigned long anon, unsigned long file)
+{
+	if (inactive_file_is_low(lruvec))
+		return false;
+
+	if (file > (anon + file) >> sc->priority)
+		return true;
+
+	return false;
+}
+
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
 				 struct lruvec *lruvec, struct scan_control *sc)
 {
@@ -1658,6 +1671,14 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 		}
 	}
 
+	/* Lots of inactive file pages? Reclaim those only. */
+	if (reclaim_file_only(lruvec, sc, anon, file)) {
+		fraction[0] = 0;
+		fraction[1] = 1;
+		denominator = 1;
+		goto out;
+	}
+
 	/*
 	 * With swappiness at 100, anonymous and file have the same priority.
 	 * This scanning priority is essentially the inverse of IO cost.
@@ -1922,8 +1943,8 @@ static void age_recent_pressure(struct lruvec *lruvec, struct zone *zone)
  * should always be larger than recent_rotated, and the size should
  * always be larger than recent_pressure.
  */
-static u64 reclaim_score(struct mem_cgroup *memcg,
-			 struct lruvec *lruvec)
+static u64 reclaim_score(struct mem_cgroup *memcg, struct lruvec *lruvec,
+			 struct scan_control *sc)
 {
 	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
 	u64 anon, file;
@@ -1949,6 +1970,14 @@ static u64 reclaim_score(struct mem_cgroup *memcg,
 		anon *= 10000;
 	}
 
+	/*
+	 * Prefer reclaiming from an lruvec with lots of inactive file
+	 * pages. Once those have been reclaimed, the score will drop so
+	 * far we will pick another lruvec to reclaim from.
+	 */
+	if (reclaim_file_only(lruvec, sc, anon, file))
+		file *= 100;
+
 	return max(anon, file);
 }
 
@@ -1977,7 +2006,7 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
 
 		age_recent_pressure(lruvec, zone);
 
-		score = reclaim_score(memcg, lruvec);
+		score = reclaim_score(memcg, lruvec, sc);
 
 		/* Pick the lruvec with the highest score. */
 		if (score > max_score) {
@@ -2002,7 +2031,7 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
 	 */
 	do {
 		shrink_lruvec(victim_lruvec, sc);
-		score = reclaim_score(memcg, victim_lruvec);
+		score = reclaim_score(memcg, victim_lruvec, sc);
 	} while (sc->nr_to_reclaim > 0 && score > max_score / 2);
 
 	mem_cgroup_put(victim_memcg);

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