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

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.

Link: https://lore.kernel.org/20261019185002.3428594-1-gourry@gourry.net
Fixes: b980077899 ("mm: introduce per-node proactive reclaim interface")
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Harry Yoo (Meta) <harry@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Yosry Ahmed <yosry@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Reviewed-by: Balbir Singh <balbirs@nvidia.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Xueyuan Chen <xueyuan.chen21@gmail.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: Vishal Moola (Fractile) <vishal.moola@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Qi Zheng <qi.zheng@linux.dev>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>

mm/vmscan.c

@@ -8185,7 +8185,7 @@ 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,