From: MengEn Sun <mengensun@xxxxxxxxxxx>
When a cpu entring NOHZ full, quiet_vmstat may flush percpu
zonestats and nodestats.
The vmstat_shepherd only check percpu zonestats and nodestats
to determine whether it is necessary to fire vmstat_update on
the target cpu for now.
If a process on a certain CPU allocates a large amount of memory,
then frees that memory, and subsequently the CPU enters NOHZ, and
the process not freeing and allocating memory anymore,the
vmstat_update not being executed on the cpu. Because
vmstat_shepherd may not see zonestats and nodestats of the cpu
changed, so may resulting in vmstat_update on the cpu not fired
for a long time.
While, This seems to be fine:
- if freeing and allocating memory occur later, it may the
high_max may be adjust automatically
- If memory is tight, the memory reclamation process will
release the pcp
Whatever, we make vmstat_shepherd to checking whether we need
decay pcp high_max, and fire pcp_decay_high early if we need.
Fixes: 51a755c56dc0 ("mm: tune PCP high automatically")
Reviewed-by: Jinliang Zheng <alexjlzheng@xxxxxxxxxxx>
Signed-off-by: MengEn Sun <mengensun@xxxxxxxxxxx>
---
changelog:
v1: https://lore.kernel.org/lkml/20241012154328.015f57635566485ad60712f3@xxxxxxxxxxxxxxxxxxxx/T/#t
v2: Make the commit message clearer by adding some comments.
---
mm/vmstat.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1917c034c045..07b494b06872 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -2024,8 +2024,17 @@ static bool need_update(int cpu)
for_each_populated_zone(zone) {
struct per_cpu_zonestat *pzstats = per_cpu_ptr(zone->per_cpu_zonestats, cpu);
+ struct per_cpu_pages *pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
struct per_cpu_nodestat *n;
+ /* per_cpu_nodestats and per_cpu_zonestats maybe flush when cpu
+ * entering NOHZ full, see quiet_vmstat. so, we check pcp
+ * high_{min,max} to determine whether it is necessary to run
+ * decay_pcp_high on the corresponding CPU
+ */
+ if (pcp->high_max > pcp->high_min)
+ return true;
+
/*
* The fast way of checking if there are any vmstat diffs.
*/
--
2.43.5
