From 430e4cdcc6002db49814780e105b8e534b614fcc Mon Sep 17 00:00:00 2001 From: Ridong Chen Date: Fri, 24 Jul 2026 11:34:35 +0800 Subject: [PATCH] mm/mglru: fix anon-only reclaim evicting file pages when swappiness=max The previous patch fixed this issue for the traditional LRU. The same problem exists in MGLRU [1]: when swappiness=max (SWAPPINESS_ANON_ONLY) is set, reclaim is expected to evict anonymous pages exclusively, but file pages can still be reclaimed when anonymous pages cannot be reclaimed (e.g. no swap and no demotion target). Fix it the same way as the traditional LRU: keep returning SWAPPINESS_ANON_ONLY in get_swappiness(), and return 0 from get_nr_to_scan() when SWAPPINESS_ANON_ONLY is set but anon pages cannot be reclaimed. Since get_nr_to_scan() decides how much MGLRU scans, returning 0 skips the scan entirely and avoids the useless scan work when there is nothing eligible to reclaim. The test result: Before fix: # cat /sys/kernel/mm/lru_gen/enabled 0x0007 # cat memory.stat anon 204800 file 67108864 ... pgsteal_proactive 0 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 0 ... pgsteal_proactive 16384 pgscan_proactive 16384 After fix: # cat memory.stat anon 188416 file 67215360 kernel 1970176 ... pgsteal_proactive 0 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 204800 file 67215360 ... pgsteal_proactive 0 pgscan_proactive 0 Link: https://lore.kernel.org/20260724033435.2573323-5-ridong.chen@linux.dev Link: https://sashiko.dev/#/patchset/20260717113300.214717-1-ridong.chen@linux.dev [1] Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim") Signed-off-by: Ridong Chen Reviewed-by: Kairui Song Reviewed-by: Barry Song Reviewed-by: Baolin Wang Cc: Axel Rasmussen Cc: David Hildenbrand Cc: Davidlohr Bueso Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Muchun Song Cc: Qi Zheng Cc: Roman Gushchin Cc: Shakeel Butt Cc: Wei Xu Cc: Yuanchu Xie Cc: Zhongkun He Signed-off-by: Andrew Morton --- mm/vmscan.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index b992f4e2e698..bc324e37c5f1 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2701,6 +2701,10 @@ static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc) { struct mem_cgroup *memcg = lruvec_memcg(lruvec); struct pglist_data *pgdat = lruvec_pgdat(lruvec); + int swappiness = sc_swappiness(sc, memcg); + + if (swappiness == SWAPPINESS_ANON_ONLY) + return swappiness; if (!sc->may_swap) return 0; @@ -2709,7 +2713,7 @@ static int get_swappiness(struct lruvec *lruvec, struct scan_control *sc) mem_cgroup_get_nr_swap_pages(memcg) < MIN_LRU_BATCH) return 0; - return sc_swappiness(sc, memcg); + return swappiness; } static int get_nr_gens(struct lruvec *lruvec, int type) @@ -4911,6 +4915,20 @@ static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, struct mem_cgroup *memcg, int swappiness) { unsigned long nr_to_scan, evictable; + struct pglist_data *pgdat = lruvec_pgdat(lruvec); + + /* + * Proactive reclaim initiated by userspace for anonymous memory only. + * SWAPPINESS_ANON_ONLY is set only on the proactive reclaim path, so + * warn if it shows up elsewhere. When anon cannot be reclaimed (e.g. + * no swap), return 0 to skip the scan entirely, avoiding useless scan + * work when there is nothing eligible to reclaim. + */ + if (swappiness == SWAPPINESS_ANON_ONLY) { + WARN_ON_ONCE(!sc->proactive); + if (!can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) + return 0; + } evictable = lruvec_evictable_size(lruvec, swappiness);