+ mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list.patch added to mm-new branch

+ mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/vmscan: select the closest preferred node in demote_folio_list()
has been added to the -mm mm-new branch.  Its filename is
     mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

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------------------------------------------------------
From: Bing Jiao <bingjiao@google.com>
Subject: mm/vmscan: select the closest preferred node in demote_folio_list()
Date: Wed, 14 Jan 2026 20:53:03 +0000

The preferred demotion node (migration_target_control.nid) should be the
one closest to the source node to minimize migration latency.  Currently,
a discrepancy exists where demote_folio_list() randomly selects an allowed
node if the preferred node from next_demotion_node() is not set in
mems_effective.

To address it, update next_demotion_node() to select a preferred target
against allowed nodes; and to return the closest demotion target if all
preferred nodes are not in mems_effective via next_demotion_node().

It ensures that the preferred demotion target is consistently the closest
available node to the source node.

Link: https://lkml.kernel.org/r/20260114205305.2869796-3-bingjiao@google.com
Signed-off-by: Bing Jiao <bingjiao@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Gregory Price <gourry@gourry.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/memory-tiers.h |    6 +++---
 mm/memory-tiers.c            |   21 ++++++++++++++++-----
 mm/vmscan.c                  |    5 ++---
 3 files changed, 21 insertions(+), 11 deletions(-)

--- a/include/linux/memory-tiers.h~mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list
+++ a/include/linux/memory-tiers.h
@@ -53,11 +53,11 @@ struct memory_dev_type *mt_find_alloc_me
 						  struct list_head *memory_types);
 void mt_put_memory_types(struct list_head *memory_types);
 #ifdef CONFIG_MIGRATION
-int next_demotion_node(int node);
+int next_demotion_node(int node, const nodemask_t *allowed_mask);
 void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets);
 bool node_is_toptier(int node);
 #else
-static inline int next_demotion_node(int node)
+static inline int next_demotion_node(int node, const nodemask_t *allowed_mask)
 {
 	return NUMA_NO_NODE;
 }
@@ -101,7 +101,7 @@ static inline void clear_node_memory_typ
 
 }
 
-static inline int next_demotion_node(int node)
+static inline int next_demotion_node(int node, const nodemask_t *allowed_mask)
 {
 	return NUMA_NO_NODE;
 }
--- a/mm/memory-tiers.c~mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list
+++ a/mm/memory-tiers.c
@@ -320,16 +320,17 @@ void node_get_allowed_targets(pg_data_t
 /**
  * next_demotion_node() - Get the next node in the demotion path
  * @node: The starting node to lookup the next node
+ * @allowed_mask: The pointer to allowed node mask
  *
  * Return: node id for next memory node in the demotion path hierarchy
  * from @node; NUMA_NO_NODE if @node is terminal.  This does not keep
  * @node online or guarantee that it *continues* to be the next demotion
  * target.
  */
-int next_demotion_node(int node)
+int next_demotion_node(int node, const nodemask_t *allowed_mask)
 {
 	struct demotion_nodes *nd;
-	int target;
+	nodemask_t mask;
 
 	if (!node_demotion)
 		return NUMA_NO_NODE;
@@ -344,6 +345,10 @@ int next_demotion_node(int node)
 	 * node_demotion[] reads need to be consistent.
 	 */
 	rcu_read_lock();
+	/* Filter out nodes that are not in allowed_mask. */
+	nodes_and(mask, nd->preferred, *allowed_mask);
+	rcu_read_unlock();
+
 	/*
 	 * If there are multiple target nodes, just select one
 	 * target node randomly.
@@ -356,10 +361,16 @@ int next_demotion_node(int node)
 	 * caching issue, which seems more complicated. So selecting
 	 * target node randomly seems better until now.
 	 */
-	target = node_random(&nd->preferred);
-	rcu_read_unlock();
+	if (!nodes_empty(mask))
+		return node_random(&mask);
 
-	return target;
+	/*
+	 * Preferred nodes are not in allowed_mask. Filp bits in
+	 * allowed_mask as used node mask. Then, use it to get the
+	 * closest demotion target.
+	 */
+	nodes_complement(mask, *allowed_mask);
+	return find_next_best_node(node, &mask);
 }
 
 static void disable_all_demotion_targets(void)
--- a/mm/vmscan.c~mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list
+++ a/mm/vmscan.c
@@ -1027,12 +1027,11 @@ static unsigned int demote_folio_list(st
 	if (nodes_empty(allowed_mask))
 		return 0;
 
-	target_nid = next_demotion_node(pgdat->node_id);
+	target_nid = next_demotion_node(pgdat->node_id, &allowed_mask);
 	if (target_nid == NUMA_NO_NODE)
 		/* No lower-tier nodes or nodes were hot-unplugged. */
 		return 0;
-	if (!node_isset(target_nid, allowed_mask))
-		target_nid = node_random(&allowed_mask);
+
 	mtc.nid = target_nid;
 
 	/* Demotion ignores all cpuset and mempolicy settings */
_

Patches currently in -mm which might be from bingjiao@google.com are

mm-vmscan-fix-demotion-targets-checks-in-reclaim-demotion.patch
mm-vmscan-select-the-closest-perferred-node-in-demote_folio_list.patch