[PATCH 4/4] mm/vmscan: Consider anonymous pages without swap

[Dave Hansen]

From: Keith Busch <keith.busch@xxxxxxxxx>

Age and reclaim anonymous pages if a migration path is available. The
node has other recourses for inactive anonymous pages beyond swap,

Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
Co-developed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---

 b/include/linux/swap.h |   20 ++++++++++++++++++++
 b/mm/vmscan.c          |   10 +++++-----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff -puN include/linux/swap.h~0006-mm-vmscan-Consider-anonymous-pages-without-swap include/linux/swap.h
--- a/include/linux/swap.h~0006-mm-vmscan-Consider-anonymous-pages-without-swap	2019-10-16 15:06:59.474952590 -0700
+++ b/include/linux/swap.h	2019-10-16 15:06:59.481952590 -0700
@@ -680,5 +680,25 @@ static inline bool mem_cgroup_swap_full(
 }
 #endif
 
+static inline bool reclaim_anon_pages(struct mem_cgroup *memcg,
+				      int node_id)
+{
+	/* Always age anon pages when we have swap */
+	if (memcg == NULL) {
+		if (get_nr_swap_pages() > 0)
+			return true;
+	} else {
+		if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
+			return true;
+	}
+
+	/* Also age anon pages if we can auto-migrate them */
+	if (next_migration_node(node_id) >= 0)
+		return true;
+
+	/* No way to reclaim anon pages */
+	return false;
+}
+
 #endif /* __KERNEL__*/
 #endif /* _LINUX_SWAP_H */
diff -puN mm/vmscan.c~0006-mm-vmscan-Consider-anonymous-pages-without-swap mm/vmscan.c
--- a/mm/vmscan.c~0006-mm-vmscan-Consider-anonymous-pages-without-swap	2019-10-16 15:06:59.477952590 -0700
+++ b/mm/vmscan.c	2019-10-16 15:06:59.482952590 -0700
@@ -327,7 +327,7 @@ unsigned long zone_reclaimable_pages(str
 
 	nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
 		zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
-	if (get_nr_swap_pages() > 0)
+	if (reclaim_anon_pages(NULL, zone_to_nid(zone)))
 		nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
 			zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
 
@@ -2166,7 +2166,7 @@ static bool inactive_list_is_low(struct
 	 * If we don't have swap space, anonymous page deactivation
 	 * is pointless.
 	 */
-	if (!file && !total_swap_pages)
+	if (!file && !reclaim_anon_pages(NULL, pgdat->node_id))
 		return false;
 
 	inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
@@ -2241,7 +2241,7 @@ static void get_scan_count(struct lruvec
 	enum lru_list lru;
 
 	/* If we have no swap space, do not bother scanning anon pages. */
-	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
+	if (!sc->may_swap || !reclaim_anon_pages(memcg, pgdat->node_id)) {
 		scan_balance = SCAN_FILE;
 		goto out;
 	}
@@ -2604,7 +2604,7 @@ static inline bool should_continue_recla
 	 */
 	pages_for_compaction = compact_gap(sc->order);
 	inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
-	if (get_nr_swap_pages() > 0)
+	if (!reclaim_anon_pages(NULL, pgdat->node_id))
 		inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
 	if (sc->nr_reclaimed < pages_for_compaction &&
 			inactive_lru_pages > pages_for_compaction)
@@ -3289,7 +3289,7 @@ static void age_active_anon(struct pglis
 {
 	struct mem_cgroup *memcg;
 
-	if (!total_swap_pages)
+	if (!reclaim_anon_pages(NULL, pgdat->node_id))
 		return;
 
 	memcg = mem_cgroup_iter(NULL, NULL, NULL);
_