[PATCH v4 2/2] mm/vmscan: add tracepoint and reason for kswapd_failures reset
From: Jiayuan Chen
Date: Mon Jan 19 2026 - 21:45:04 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 kswapd_clear_hopeless() as a wrapper function to
centralize kswapd_failures reset logic.
2. Introduce kswapd_test_hopeless() to encapsulate hopeless node
checks, replacing all open-coded kswapd_failures comparisons.
3. Add kswapd_clear_hopeless_reason enum to distinguish reset sources:
- KSWAPD_CLEAR_HOPELESS_KSWAPD: reset from kswapd context
- KSWAPD_CLEAR_HOPELESS_DIRECT: reset from direct reclaim
- KSWAPD_CLEAR_HOPELESS_PCP: reset from PCP page freeing
- KSWAPD_CLEAR_HOPELESS_OTHER: reset from other paths
4. Add tracepoints for better observability:
- mm_vmscan_kswapd_clear_hopeless: traces each reset with reason
- mm_vmscan_kswapd_reclaim_fail: traces each kswapd reclaim failure
Test results:
$ trace-cmd record -e vmscan:mm_vmscan_kswapd_clear_hopeless -e vmscan:mm_vmscan_kswapd_reclaim_fail
$ # generate memory pressure
$ trace-cmd report
cpus=4
kswapd0-71 [000] 27.216563: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=1
kswapd0-71 [000] 27.217169: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=2
kswapd0-71 [000] 27.217764: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=3
kswapd0-71 [000] 27.218353: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=4
kswapd0-71 [000] 27.218993: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=5
kswapd0-71 [000] 27.219744: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=6
kswapd0-71 [000] 27.220488: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=7
kswapd0-71 [000] 27.221206: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=8
kswapd0-71 [000] 27.221806: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=9
kswapd0-71 [000] 27.222634: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=10
kswapd0-71 [000] 27.223286: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=11
kswapd0-71 [000] 27.223894: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=12
kswapd0-71 [000] 27.224712: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=13
kswapd0-71 [000] 27.225424: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=14
kswapd0-71 [000] 27.226082: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=15
kswapd0-71 [000] 27.226810: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=16
kswapd1-72 [002] 27.386869: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=1
kswapd1-72 [002] 27.387435: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=2
kswapd1-72 [002] 27.388016: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=3
kswapd1-72 [002] 27.388586: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=4
kswapd1-72 [002] 27.389155: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=5
kswapd1-72 [002] 27.389723: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=6
kswapd1-72 [002] 27.390292: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=7
kswapd1-72 [002] 27.392364: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=8
kswapd1-72 [002] 27.392934: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=9
kswapd1-72 [002] 27.393504: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=10
kswapd1-72 [002] 27.394073: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=11
kswapd1-72 [002] 27.394899: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=12
kswapd1-72 [002] 27.395472: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=13
kswapd1-72 [002] 27.396055: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=14
kswapd1-72 [002] 27.396628: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=15
kswapd1-72 [002] 27.397199: mm_vmscan_kswapd_reclaim_fail: nid=1 failures=16
kworker/u18:0-40 [002] 27.410151: mm_vmscan_kswapd_clear_hopeless: nid=0 reason=DIRECT
kswapd0-71 [000] 27.439454: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=1
kswapd0-71 [000] 27.440048: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=2
kswapd0-71 [000] 27.440634: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=3
kswapd0-71 [000] 27.441211: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=4
kswapd0-71 [000] 27.441787: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=5
kswapd0-71 [000] 27.442363: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=6
kswapd0-71 [000] 27.443030: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=7
kswapd0-71 [000] 27.443725: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=8
kswapd0-71 [000] 27.444315: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=9
kswapd0-71 [000] 27.444898: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=10
kswapd0-71 [000] 27.445476: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=11
kswapd0-71 [000] 27.446053: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=12
kswapd0-71 [000] 27.446646: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=13
kswapd0-71 [000] 27.447230: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=14
kswapd0-71 [000] 27.447812: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=15
kswapd0-71 [000] 27.448391: mm_vmscan_kswapd_reclaim_fail: nid=0 failures=16
ann-423 [003] 28.028285: mm_vmscan_kswapd_clear_hopeless: nid=0 reason=PCP
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
---
include/linux/mmzone.h | 19 ++++++++++---
include/trace/events/vmscan.h | 51 +++++++++++++++++++++++++++++++++++
mm/memory-tiers.c | 2 +-
mm/page_alloc.c | 4 +--
mm/show_mem.c | 3 +--
mm/vmscan.c | 29 +++++++++++++-------
mm/vmstat.c | 2 +-
7 files changed, 91 insertions(+), 19 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 3a0f52188ff6..d26fdd48f106 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1534,16 +1534,27 @@ static inline unsigned long pgdat_end_pfn(pg_data_t *pgdat)
#include <linux/memory_hotplug.h>
void build_all_zonelists(pg_data_t *pgdat);
-void wakeup_kswapd(struct zone *zone, gfp_t gfp_mask, int order,
- enum zone_type highest_zoneidx);
-void kswapd_try_clear_hopeless(struct pglist_data *pgdat,
- unsigned int order, int highest_zoneidx);
bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
int highest_zoneidx, unsigned int alloc_flags,
long free_pages);
bool zone_watermark_ok(struct zone *z, unsigned int order,
unsigned long mark, int highest_zoneidx,
unsigned int alloc_flags);
+
+enum kswapd_clear_hopeless_reason {
+ KSWAPD_CLEAR_HOPELESS_OTHER = 0,
+ KSWAPD_CLEAR_HOPELESS_KSWAPD,
+ KSWAPD_CLEAR_HOPELESS_DIRECT,
+ KSWAPD_CLEAR_HOPELESS_PCP,
+};
+
+void wakeup_kswapd(struct zone *zone, gfp_t gfp_mask, int order,
+ enum zone_type highest_zoneidx);
+void kswapd_try_clear_hopeless(struct pglist_data *pgdat,
+ unsigned int order, int highest_zoneidx);
+void kswapd_clear_hopeless(pg_data_t *pgdat, enum kswapd_clear_hopeless_reason reason);
+bool kswapd_test_hopeless(pg_data_t *pgdat);
+
/*
* Memory initialization context, use to differentiate memory added by
* the platform statically or via memory hotplug interface.
diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
index 490958fa10de..ea58e4656abf 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(KSWAPD_CLEAR_HOPELESS_OTHER);
+TRACE_DEFINE_ENUM(KSWAPD_CLEAR_HOPELESS_KSWAPD);
+TRACE_DEFINE_ENUM(KSWAPD_CLEAR_HOPELESS_DIRECT);
+TRACE_DEFINE_ENUM(KSWAPD_CLEAR_HOPELESS_PCP);
+
+#define kswapd_clear_hopeless_reason_ops \
+ {KSWAPD_CLEAR_HOPELESS_KSWAPD, "KSWAPD"}, \
+ {KSWAPD_CLEAR_HOPELESS_DIRECT, "DIRECT"}, \
+ {KSWAPD_CLEAR_HOPELESS_PCP, "PCP"}, \
+ {KSWAPD_CLEAR_HOPELESS_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_kswapd_clear_hopeless,
+
+ 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, kswapd_clear_hopeless_reason_ops))
+);
#endif /* _TRACE_VMSCAN_H */
/* This part must be outside protection */
diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
index 864811fff409..d6ef5ba8e70a 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);
+ kswapd_clear_hopeless(pgdat, KSWAPD_CLEAR_HOPELESS_OTHER);
}
return count;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c380f063e8b7..1b1dedc7ede1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2916,9 +2916,9 @@ static bool free_frozen_page_commit(struct zone *zone,
* 'hopeless node' to stay in that state for a while. Let
* kswapd work again by resetting kswapd_failures.
*/
- if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES &&
+ if (kswapd_test_hopeless(pgdat) &&
next_memory_node(pgdat->node_id) < MAX_NUMNODES)
- atomic_set(&pgdat->kswapd_failures, 0);
+ kswapd_clear_hopeless(pgdat, KSWAPD_CLEAR_HOPELESS_PCP);
}
return ret;
}
diff --git a/mm/show_mem.c b/mm/show_mem.c
index 3a4b5207635d..24078ac3e6bc 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -278,8 +278,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
#endif
K(node_page_state(pgdat, NR_PAGETABLE)),
K(node_page_state(pgdat, NR_SECONDARY_PAGETABLE)),
- str_yes_no(atomic_read(&pgdat->kswapd_failures) >=
- MAX_RECLAIM_RETRIES),
+ str_yes_no(kswapd_test_hopeless(pgdat)),
K(node_page_state(pgdat, NR_BALLOON_PAGES)));
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ecd019b8b452..0ec2baa4ed4e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -507,7 +507,7 @@ static bool skip_throttle_noprogress(pg_data_t *pgdat)
* If kswapd is disabled, reschedule if necessary but do not
* throttle as the system is likely near OOM.
*/
- if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES)
+ if (kswapd_test_hopeless(pgdat))
return true;
/*
@@ -6453,7 +6453,7 @@ static bool allow_direct_reclaim(pg_data_t *pgdat)
int i;
bool wmark_ok;
- if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES)
+ if (kswapd_test_hopeless(pgdat))
return true;
for_each_managed_zone_pgdat(zone, pgdat, i, ZONE_NORMAL) {
@@ -6862,7 +6862,7 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order,
wake_up_all(&pgdat->pfmemalloc_wait);
/* Hopeless node, leave it to direct reclaim */
- if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES)
+ if (kswapd_test_hopeless(pgdat))
return true;
if (pgdat_balanced(pgdat, order, highest_zoneidx)) {
@@ -7134,8 +7134,11 @@ 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);
@@ -7394,7 +7397,7 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
return;
/* Hopeless node, leave it to direct reclaim if possible */
- if (atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES ||
+ if (kswapd_test_hopeless(pgdat) ||
(pgdat_balanced(pgdat, order, highest_zoneidx) &&
!pgdat_watermark_boosted(pgdat, highest_zoneidx))) {
/*
@@ -7414,9 +7417,11 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
wake_up_interruptible(&pgdat->kswapd_wait);
}
-static void kswapd_clear_hopeless(pg_data_t *pgdat)
+void kswapd_clear_hopeless(pg_data_t *pgdat, enum kswapd_clear_hopeless_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_kswapd_clear_hopeless(pgdat->node_id, reason);
}
/*
@@ -7429,7 +7434,13 @@ void kswapd_try_clear_hopeless(struct pglist_data *pgdat,
unsigned int order, int highest_zoneidx)
{
if (pgdat_balanced(pgdat, order, highest_zoneidx))
- kswapd_clear_hopeless(pgdat);
+ kswapd_clear_hopeless(pgdat, current_is_kswapd() ?
+ KSWAPD_CLEAR_HOPELESS_KSWAPD : KSWAPD_CLEAR_HOPELESS_DIRECT);
+}
+
+bool kswapd_test_hopeless(pg_data_t *pgdat)
+{
+ return atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES;
}
#ifdef CONFIG_HIBERNATION
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 65de88cdf40e..3d65f5c9c224 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1855,7 +1855,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
"\n start_pfn: %lu"
"\n reserved_highatomic: %lu"
"\n free_highatomic: %lu",
- atomic_read(&pgdat->kswapd_failures) >= MAX_RECLAIM_RETRIES,
+ kswapd_test_hopeless(pgdat),
zone->zone_start_pfn,
zone->nr_reserved_highatomic,
zone->nr_free_highatomic);
--
2.43.0