[PATCH] mm/vmscan: reclaim every zone in per-node proactive reclaim

[Gregory Price (Meta)]

user_proactive_reclaim() limits per-node reclaim to
gfp_zone(GFP_KERNEL), which is ZONE_NORMAL. Proactive reclaim serves no
allocation, but that limit makes shrink_node() skip every ZONE_MOVABLE
folio, so writing to /sys/devices/system/node/nodeN/reclaim never
reclaims a node's movable memory. A movable-only node, such as dax/kmem
or hotplugged memory onlined movable, reclaims nothing and fails with
-EAGAIN.

To reproduce, fill a movable-only node with clean page cache and write
200M to its nodeN/reclaim: the write fails with -EAGAIN and the page
cache stays. The same write to a ZONE_NORMAL node frees 200MB.

Scan every zone, as memory.reclaim does.

Fixes: b980077899ea4 ("mm: introduce per-node proactive reclaim interface")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index e82ba737c028d..90f7a7bf4e426 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -8180,7 +8180,7 @@ int user_proactive_reclaim(char *buf,
 		} else {
 			struct scan_control sc = {
 				.gfp_mask = current_gfp_context(gfp_mask),
-				.reclaim_idx = gfp_zone(gfp_mask),
+				.reclaim_idx = MAX_NR_ZONES - 1,
 				.proactive_swappiness = swappiness == -1 ? NULL : &swappiness,
 				.priority = DEF_PRIORITY,
 				.may_writepage = 1,
-- 
2.53.0-Meta