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Message-ID: <20260114205305.2869796-3-bingjiao@google.com>
Date: Wed, 14 Jan 2026 20:53:03 +0000
From: Bing Jiao <bingjiao@...gle.com>
To: bingjiao@...gle.com
Cc: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...nel.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Axel Rasmussen <axelrasmussen@...gle.com>,
Yuanchu Xie <yuanchu@...gle.com>, Wei Xu <weixugc@...gle.com>,
Johannes Weiner <hannes@...xchg.org>, Qi Zheng <zhengqi.arch@...edance.com>,
Shakeel Butt <shakeel.butt@...ux.dev>, Gregory Price <gourry@...rry.net>,
Joshua Hahn <joshua.hahnjy@...il.com>, muchun.song@...ux.dev, roman.gushchin@...ux.dev,
tj@...nel.org, longman@...hat.com, chenridong@...weicloud.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: [PATCH v9 2/2] mm/vmscan: select the closest perferred node in demote_folio_list()
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.
Signed-off-by: Bing Jiao <bingjiao@...gle.com>
---
v7 -> v8:
Fix bugs in v7.
Remove the while loop of getting the preferred node via
next_demotion_node().
Use find_next_best_node() to find the closest demotion target.
v8 -> v9:
Move allowed node checks and identification of the closest demotion
target into next_demotion_node() for better function splitting.
include/linux/memory-tiers.h | 6 +++---
mm/memory-tiers.c | 21 ++++++++++++++++-----
mm/vmscan.c | 5 ++---
3 files changed, 21 insertions(+), 11 deletions(-)
diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h
index 7a805796fcfd..96987d9d95a8 100644
--- a/include/linux/memory-tiers.h
+++ b/include/linux/memory-tiers.h
@@ -53,11 +53,11 @@ struct memory_dev_type *mt_find_alloc_memory_type(int adist,
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_type(int node, struct memory_dev_type *memt
}
-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;
}
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 864811fff409..2d6c3754e6a8 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -320,16 +320,17 @@ void node_get_allowed_targets(pg_data_t *pgdat, nodemask_t *targets)
/**
* 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)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5ea1dd2b8cce..7a631de46064 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1048,12 +1048,11 @@ static unsigned int demote_folio_list(struct list_head *demote_folios,
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 */
--
2.52.0.457.g6b5491de43-goog
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