From e26f7a91de5ca806a3413ef7dbdd3343a6aca8b7 Mon Sep 17 00:00:00 2001 From: Ridong Chen Date: Fri, 24 Jul 2026 11:34:32 +0800 Subject: [PATCH] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max Patch series "mm/vmscan: fix swappiness=max and clean up per-node proactive reclaim", v4. Fixes and one cleanup. Patch 1 fixes "swappiness=max": the anon-only test in get_scan_count() sat after the "cannot reclaim anon" check, so when no anon was reclaimable the request fell back to SCAN_FILE and evicted page cache instead. Patch 2 fixes reclaim_store() collapsing every error into -EAGAIN, so callers can no longer tell an invalid argument from a busy interface; propagate the real error code, matching the memcg path. Patch 3 drops the now-unused gfp_mask parameter from __node_reclaim(). Patch 4 fixes the same "swappiness=max" issue for MGLRU. This patch (of 4): As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks in get_scan_count(), file pages may still be evicted if can_reclaim_anon_pages() returns false, which contradicts the semantics of SWAPPINESS_ANON_ONLY. Reproducer in a cgroup holding 64M of file cache, with no swap configured: Before (file cache is wrongly evicted): # cat memory.stat anon 196608 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 4096 <- page cache evicted pgsteal_proactive 16400 pgscan_proactive 16400 After (file cache is left intact): # cat memory.stat anon 200704 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 208896 file 67178496 <- page cache untouched pgsteal_proactive 0 pgscan_proactive 0 Fix this by bailing out early when SWAPPINESS_ANON_ONLY is set and no anonymous pages are reclaimable, before falling back to file reclaim. Link: https://lore.kernel.org/20260724033435.2573323-1-ridong.chen@linux.dev Link: https://lore.kernel.org/20260724033435.2573323-2-ridong.chen@linux.dev Link: https://lore.kernel.org/cgroups/7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev/ [1] Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim") Signed-off-by: Ridong Chen Suggested-by: Qi Zheng Acked-by: Shakeel Butt Acked-by: Johannes Weiner Reviewed-by: Muchun Song Reviewed-by: Qi Zheng Reviewed-by: Barry Song Cc: Axel Rasmussen Cc: David Hildenbrand Cc: Davidlohr Bueso Cc: Kairui Song Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Roman Gushchin Cc: Wei Xu Cc: Yuanchu Xie Cc: Zhongkun He Cc: Baolin Wang Signed-off-by: Andrew Morton --- mm/vmscan.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 006829efceca..af0c42daa77d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2494,6 +2494,23 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, enum scan_balance scan_balance; enum lru_list lru; + /* + * 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), bail out instead of falling back to evicting file pages, + * which would violate the anon-only semantics. + */ + if (swappiness == SWAPPINESS_ANON_ONLY) { + WARN_ON_ONCE(!sc->proactive); + if (!can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) { + memset(nr, 0, sizeof(*nr) * NR_LRU_LISTS); + return; + } + scan_balance = SCAN_ANON; + goto out; + } + /* If we have no swap space, do not bother scanning anon folios. */ if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) { scan_balance = SCAN_FILE; @@ -2512,13 +2529,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, goto out; } - /* Proactive reclaim initiated by userspace for anonymous memory only */ - if (swappiness == SWAPPINESS_ANON_ONLY) { - WARN_ON_ONCE(!sc->proactive); - scan_balance = SCAN_ANON; - goto out; - } - /* * Do not apply any pressure balancing cleverness when the * system is close to OOM, scan both anon and file equally