[PATCH v3 2/2] mm/vmscan: add tracepoint and reason for kswapd_failures reset
From: Jiayuan Chen
Date: Wed Jan 14 2026 - 02:41:30 EST
From: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
Currently, kswapd_failures is reset in multiple places (kswapd,
direct reclaim, PCP freeing, memory-tiers), but there's no way to
trace when and why it was reset, making it difficult to debug
memory reclaim issues.
This patch:
1. Introduce pgdat_reset_kswapd_failures() as a wrapper function to
centralize kswapd_failures reset logic.
2. Add reset_kswapd_failures_reason enum to distinguish reset sources:
- RESET_KSWAPD_FAILURES_KSWAPD: reset from kswapd context
- RESET_KSWAPD_FAILURES_DIRECT: reset from direct reclaim
- RESET_KSWAPD_FAILURES_PCP: reset from PCP page freeing
- RESET_KSWAPD_FAILURES_OTHER: reset from other paths
3. Add tracepoints for better observability:
- mm_vmscan_reset_kswapd_failures: traces each reset with reason
- mm_vmscan_kswapd_reclaim_fail: traces each kswapd reclaim failure
---
Test results:
$ trace-cmd record -e vmscan:mm_vmscan_reset_kswapd_failures -e vmscan:mm_vmscan_kswapd_reclaim_fail
$ # generate memory pressure
$ trace-cmd report
cpus=4
kswapd1-73 [002] 24.863112: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=1
kswapd1-73 [002] 24.863472: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=2
kswapd1-73 [002] 24.863813: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=3
kswapd1-73 [002] 24.864141: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=4
kswapd1-73 [002] 24.864462: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=5
kswapd1-73 [002] 24.864779: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=6
kswapd1-73 [002] 24.865103: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=7
kswapd1-73 [002] 24.865421: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=8
kswapd1-73 [002] 24.865737: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=9
kswapd1-73 [002] 24.866070: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=10
kswapd1-73 [002] 24.866385: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=11
kswapd1-73 [002] 24.866701: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=12
kswapd1-73 [002] 24.867016: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=13
kswapd1-73 [002] 24.867333: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=14
kswapd1-73 [002] 24.867649: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=15
kswapd1-73 [002] 24.867965: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=16
kswapd0-72 [001] 25.020464: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=1
kswapd0-72 [001] 25.021054: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=2
kswapd0-72 [001] 25.021628: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=3
kswapd0-72 [001] 25.022217: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=4
kswapd0-72 [001] 25.022790: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=5
kswapd0-72 [001] 25.023366: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=6
kswapd0-72 [001] 25.023937: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=7
kswapd0-72 [001] 25.024511: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=8
kswapd0-72 [001] 25.025092: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=9
kswapd0-72 [001] 25.025665: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=10
kswapd0-72 [001] 25.026249: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=11
kswapd0-72 [001] 25.026824: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=12
kswapd0-72 [001] 25.027398: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=13
kswapd0-72 [001] 25.027976: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=14
kswapd0-72 [001] 25.028554: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=15
kswapd0-72 [001] 25.029140: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=16
ann-416 [002] 25.577925: mm_vmscan_reset_kswapd_failures: nid=0 reason=PCP
dd-417 [002] 35.111721: mm_vmscan_reset_kswapd_failures: nid=1 reason=DIRECT
Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
---
include/linux/mmzone.h | 9 +++++++
include/trace/events/vmscan.h | 51 +++++++++++++++++++++++++++++++++++
mm/memory-tiers.c | 2 +-
mm/page_alloc.c | 2 +-
mm/vmscan.c | 16 +++++++----
5 files changed, 73 insertions(+), 7 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 75ef7c9f9307..3f4d2928d8dc 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1531,6 +1531,15 @@ static inline unsigned long pgdat_end_pfn(pg_data_t *pgdat)
return pgdat->node_start_pfn + pgdat->node_spanned_pages;
}
+enum reset_kswapd_failures_reason {
+ RESET_KSWAPD_FAILURES_OTHER = 0,
+ RESET_KSWAPD_FAILURES_KSWAPD,
+ RESET_KSWAPD_FAILURES_DIRECT,
+ RESET_KSWAPD_FAILURES_PCP,
+};
+
+void pgdat_reset_kswapd_failures(pg_data_t *pgdat, enum reset_kswapd_failures_reason reason);
+
#include <linux/memory_hotplug.h>
void build_all_zonelists(pg_data_t *pgdat);
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 490958fa10de..0747ad2f7932 100644
--- a/include/trace/events/vmscan.h
+++ b/include/trace/events/vmscan.h
@@ -40,6 +40,16 @@
{_VMSCAN_THROTTLE_CONGESTED, "VMSCAN_THROTTLE_CONGESTED"} \
) : "VMSCAN_THROTTLE_NONE"
+TRACE_DEFINE_ENUM(RESET_KSWAPD_FAILURES_OTHER);
+TRACE_DEFINE_ENUM(RESET_KSWAPD_FAILURES_KSWAPD);
+TRACE_DEFINE_ENUM(RESET_KSWAPD_FAILURES_DIRECT);
+TRACE_DEFINE_ENUM(RESET_KSWAPD_FAILURES_PCP);
+
+#define reset_kswapd_src \
+ {RESET_KSWAPD_FAILURES_KSWAPD, "KSWAPD"}, \
+ {RESET_KSWAPD_FAILURES_DIRECT, "DIRECT"}, \
+ {RESET_KSWAPD_FAILURES_PCP, "PCP"}, \
+ {RESET_KSWAPD_FAILURES_OTHER, "OTHER"}
#define trace_reclaim_flags(file) ( \
(file ? RECLAIM_WB_FILE : RECLAIM_WB_ANON) | \
@@ -535,6 +545,47 @@ TRACE_EVENT(mm_vmscan_throttled,
__entry->usec_delayed,
show_throttle_flags(__entry->reason))
);
+
+TRACE_EVENT(mm_vmscan_kswapd_reclaim_fail,
+
+ TP_PROTO(int nid, int failures),
+
+ TP_ARGS(nid, failures),
+
+ TP_STRUCT__entry(
+ __field(int, nid)
+ __field(int, failures)
+ ),
+
+ TP_fast_assign(
+ __entry->nid = nid;
+ __entry->failures = failures;
+ ),
+
+ TP_printk("nid=%d failures=%d",
+ __entry->nid, __entry->failures)
+);
+
+TRACE_EVENT(mm_vmscan_reset_kswapd_failures,
+
+ TP_PROTO(int nid, int reason),
+
+ TP_ARGS(nid, reason),
+
+ TP_STRUCT__entry(
+ __field(int, nid)
+ __field(int, reason)
+ ),
+
+ TP_fast_assign(
+ __entry->nid = nid;
+ __entry->reason = reason;
+ ),
+
+ TP_printk("nid=%d reason=%s",
+ __entry->nid,
+ __print_symbolic(__entry->reason, reset_kswapd_src))
+);
#endif /* _TRACE_VMSCAN_H */
/* This part must be outside protection */
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 864811fff409..8188f341bd77 100644
--- a/mm/memory-tiers.c
+++ b/mm/memory-tiers.c
@@ -956,7 +956,7 @@ static ssize_t demotion_enabled_store(struct kobject *kobj,
struct pglist_data *pgdat;
for_each_online_pgdat(pgdat)
- atomic_set(&pgdat->kswapd_failures, 0);
+ pgdat_reset_kswapd_failures(pgdat, RESET_KSWAPD_FAILURES_OTHER);
}
return count;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c380f063e8b7..cadf2c8b06a5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2918,7 +2918,7 @@ static bool free_frozen_page_commit(struct zone *zone,
*/
if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES &&
next_memory_node(pgdat->node_id) < MAX_NUMNODES)
- atomic_set(&pgdat->kswapd_failures, 0);
+ pgdat_reset_kswapd_failures(pgdat, RESET_KSWAPD_FAILURES_PCP);
}
return ret;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6fd100130987..8d9f3d29fe3b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2650,9 +2650,11 @@ static bool can_age_anon_pages(struct lruvec *lruvec,
lruvec_memcg(lruvec));
}
-static void pgdat_reset_kswapd_failures(pg_data_t *pgdat)
+void pgdat_reset_kswapd_failures(pg_data_t *pgdat, enum reset_kswapd_failures_reason reason)
{
- atomic_set(&pgdat->kswapd_failures, 0);
+ /* Only trace actual resets, not redundant zero-to-zero */
+ if (atomic_xchg(&pgdat->kswapd_failures, 0))
+ trace_mm_vmscan_reset_kswapd_failures(pgdat->node_id, reason);
}
/*
@@ -2666,7 +2668,8 @@ static inline void pgdat_try_reset_kswapd_failures(struct pglist_data *pgdat,
struct scan_control *sc)
{
if (pgdat_balanced(pgdat, sc->order, sc->reclaim_idx))
- pgdat_reset_kswapd_failures(pgdat);
+ pgdat_reset_kswapd_failures(pgdat, current_is_kswapd() ?
+ RESET_KSWAPD_FAILURES_KSWAPD : RESET_KSWAPD_FAILURES_DIRECT);
}
#ifdef CONFIG_LRU_GEN
@@ -7153,8 +7156,11 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
* watermark_high at this point. We need to avoid increasing the
* failure count to prevent the kswapd thread from stopping.
*/
- if (!sc.nr_reclaimed && !boosted)
- atomic_inc(&pgdat->kswapd_failures);
+ if (!sc.nr_reclaimed && !boosted) {
+ int fail_cnt = atomic_inc_return(&pgdat->kswapd_failures);
+ /* kswapd context, low overhead to trace every failure */
+ trace_mm_vmscan_kswapd_reclaim_fail(pgdat->node_id, fail_cnt);
+ }
out:
clear_reclaim_active(pgdat, highest_zoneidx);
--
2.43.0