* [PATCH -v4 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter
[not found] <20260723032434.2016749-1-ridong.chen@linux.dev>
@ 2026-07-23 3:24 ` Ridong
2026-07-24 15:53 ` Shakeel Butt
0 siblings, 1 reply; 2+ messages in thread
From: Ridong @ 2026-07-23 3:24 UTC (permalink / raw)
To: Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt,
Andrew Morton, Chris Li, Kairui Song
Cc: Muchun Song, Kemeng Shi, Nhat Pham, Baoquan He, Barry Song,
Youngjun Park, David Hildenbrand, Qi Zheng, Lorenzo Stoakes,
Axel Rasmussen, Yuanchu Xie, Wei Xu, Davidlohr Bueso, cgroups,
linux-mm, linux-kernel, Song Hu, Ridong Chen, Ridong Chen, stable
From: Ridong Chen <chenridong@xiaomi.com>
sc_swappiness() had two separate definitions depending on
CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
vm_swappiness, ignoring the proactive_swappiness value passed
through scan_control. This caused the swappiness parameter
written to /sys/devices/system/node/nodeX/reclaim to have no
effect when CONFIG_MEMCG is disabled.
Fix this by consolidating sc_swappiness() into a single definition
that checks sc->proactive_swappiness first, then falls back to
mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
and !CONFIG_MEMCG.
Before fix (swappiness=max ignored, mostly file pages reclaimed):
# cat /proc/sys/vm/swappiness
60
# cat /proc/vmstat | grep pgsteal
pgsteal_kswapd 0
pgsteal_direct 0
pgsteal_khugepaged 0
pgsteal_proactive 1840
pgsteal_anon 25
pgsteal_file 1815
# echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
# cat /proc/vmstat | grep pgsteal
pgsteal_kswapd 0
pgsteal_direct 0
pgsteal_khugepaged 0
pgsteal_proactive 18013
pgsteal_anon 337
pgsteal_file 17676
After fix (swappiness=max honored, anon pages reclaimed as expected):
# cat /proc/vmstat | grep pgsteal
pgsteal_kswapd 0
pgsteal_direct 0
pgsteal_khugepaged 0
pgsteal_proactive 0
pgsteal_anon 0
pgsteal_file 0
# echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
# cat /proc/vmstat | grep pgsteal
pgsteal_kswapd 0
pgsteal_direct 0
pgsteal_khugepaged 0
pgsteal_proactive 16283
pgsteal_anon 16283
pgsteal_file 0
Cc: stable@vger.kernel.org # 6.17+
Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Qi Zheng <qi.zheng@linux.dev>
Tested-by: Song Hu <husong@kylinos.cn>
Reviewed-by: Song Hu <husong@kylinos.cn>
Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
---
mm/vmscan.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 06e103f9781e..155167b3614b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -199,6 +199,13 @@ struct scan_control {
*/
int vm_swappiness = 60;
+static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
+{
+ if (sc->proactive && sc->proactive_swappiness)
+ return *sc->proactive_swappiness;
+ return mem_cgroup_swappiness(memcg);
+}
+
#ifdef CONFIG_MEMCG
/* Returns true for reclaim through cgroup limits or cgroup interfaces. */
@@ -239,13 +246,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
#endif
return false;
}
-
-static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
-{
- if (sc->proactive && sc->proactive_swappiness)
- return *sc->proactive_swappiness;
- return mem_cgroup_swappiness(memcg);
-}
#else
static bool cgroup_reclaim(struct scan_control *sc)
{
@@ -261,11 +261,6 @@ static bool writeback_throttling_sane(struct scan_control *sc)
{
return true;
}
-
-static int sc_swappiness(struct scan_control *sc, struct mem_cgroup *memcg)
-{
- return READ_ONCE(vm_swappiness);
-}
#endif
static void set_task_reclaim_state(struct task_struct *task,
--
2.34.1
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