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Subject[patch] mm, vmscan: avoid thrashing anon lru when free + file is low
The purpose of the code that commit 623762517e23 ("revert 'mm: vmscan: do
not swap anon pages just because free+file is low'") reintroduces is to
prefer swapping anonymous memory rather than trashing the file lru.

If all anonymous memory is unevictable, however, this insistance on
SCAN_ANON ends up thrashing that lru instead.

Check that enough evictable anon memory is actually on this lruvec before
insisting on SCAN_ANON. SWAP_CLUSTER_MAX is used as the threshold to
determine if only scanning anon is beneficial.

Otherwise, fallback to balanced reclaim so the file lru doesn't remain
untouched.

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/vmscan.c | 41 +++++++++++++++++++++++------------------
1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2186,26 +2186,31 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
* anon pages. Try to detect this based on file LRU size.
*/
if (global_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;
+ anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, sc->reclaim_idx) +
+ lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx);
+ if (likely(anon >= SWAP_CLUSTER_MAX)) {
+ unsigned long total_high_wmark = 0;
+ unsigned long pgdatfile;
+ unsigned long pgdatfree;
+ int z;
+
+ 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);
- }
+ total_high_wmark += high_wmark_pages(zone);
+ }

- if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
- scan_balance = SCAN_ANON;
- goto out;
+ if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
+ scan_balance = SCAN_ANON;
+ goto out;
+ }
}
}

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