When file pages are lower than the watermark on a node, we try to
force scan anonymous pages to counter-act the balancing algorithms
preference for new file pages when they are likely thrashing. This is
node-level decision, but it's currently made each time we look at an
lruvec. This is unnecessarily expensive and also a layering violation
that makes the code harder to understand.
Clean this up by making the check once per node and setting a flag in
the scan_control.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/vmscan.c | 80 ++++++++++++++++++++++++++++-------------------------
1 file changed, 42 insertions(+), 38 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb535c572733..cabf94dfa92d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -104,6 +104,9 @@ struct scan_control {
/* One of the zones is ready for compaction */
unsigned int compaction_ready:1;
+ /* The file pages on the current node are dangerously low */
+ unsigned int file_is_tiny:1;
+
/* Allocation order */
s8 order;
@@ -2219,45 +2222,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
}
/*
- * Prevent the reclaimer from falling into the cache trap: as
- * cache pages start out inactive, every cache fault will tip
- * the scan balance towards the file LRU. And as the file LRU
- * shrinks, so does the window for rotation from references.
- * This means we have a runaway feedback loop where a tiny
- * thrashing file LRU becomes infinitely more attractive than
- * anon pages. Try to detect this based on file LRU size.
+ * If the system is almost out of file pages, force-scan anon.
+ * But only if there are enough inactive anonymous pages on
+ * the LRU. Otherwise, the small LRU gets thrashed.
*/
- if (!cgroup_reclaim(sc)) {
- unsigned long pgdatfile;
- unsigned long pgdatfree;
- int z;
- unsigned long total_high_wmark = 0;
-
- pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
- pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
- node_page_state(pgdat, NR_INACTIVE_FILE);
-
- for (z = 0; z < MAX_NR_ZONES; z++) {
- struct zone *zone = &pgdat->node_zones[z];
- if (!managed_zone(zone))
- continue;
-
- total_high_wmark += high_wmark_pages(zone);
- }
-
- if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
- /*
- * Force SCAN_ANON if there are enough inactive
- * anonymous pages on the LRU in eligible zones.
- * Otherwise, the small LRU gets thrashed.
- */
- if (!inactive_list_is_low(lruvec, false, sc, false) &&
- lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
- >> sc->priority) {
- scan_balance = SCAN_ANON;
- goto out;
- }
- }
+ if (sc->file_is_tiny &&
+ !inactive_list_is_low(lruvec, false, sc, false) &&
+ lruvec_lru_size(lruvec, LRU_INACTIVE_ANON,
+ sc->reclaim_idx) >> sc->priority) {
+ scan_balance = SCAN_ANON;
+ goto out;
}
/*
@@ -2718,6 +2692,36 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
nr_reclaimed = sc->nr_reclaimed;
nr_scanned = sc->nr_scanned;
+ /*
+ * Prevent the reclaimer from falling into the cache trap: as
+ * cache pages start out inactive, every cache fault will tip
+ * the scan balance towards the file LRU. And as the file LRU
+ * shrinks, so does the window for rotation from references.
+ * This means we have a runaway feedback loop where a tiny
+ * thrashing file LRU becomes infinitely more attractive than
+ * anon pages. Try to detect this based on file LRU size.
+ */
+ if (!cgroup_reclaim(sc)) {
+ unsigned long file;
+ unsigned long free;
+ int z;
+ unsigned long total_high_wmark = 0;
+
+ free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
+ file = node_page_state(pgdat, NR_ACTIVE_FILE) +
+ node_page_state(pgdat, NR_INACTIVE_FILE);
+
+ for (z = 0; z < MAX_NR_ZONES; z++) {
+ struct zone *zone = &pgdat->node_zones[z];
+ if (!managed_zone(zone))
+ continue;
+
+ total_high_wmark += high_wmark_pages(zone);
+ }
+
+ sc->file_is_tiny = file + free <= total_high_wmark;
+ }
+
shrink_node_memcgs(pgdat, sc);
if (reclaim_state) {
--
2.21.0
