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mm/vmscan: add tracepoint and reason for kswapd_failures reset

Browse source 
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

Link: https://lkml.kernel.org/r/20260120024402.387576-3-jiayuan.chen@linux.dev
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>	[tracing]
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jiayuan Chen 2026-01-20 10:43:49 +08:00 • committed by Andrew Morton
parent dc9fe9b705
commit a45088376d
7 changed files with 91 additions and 19 deletions
Download patch file Download diff file Expand all files Collapse all files

19
include/linux/mmzone.h
View file

@ -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.

51
include/trace/events/vmscan.h
View file

@ -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 */

2
mm/memory-tiers.c
View file

@ -955,7 +955,7 @@ 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;

4
mm/page_alloc.c
View file

@ -2945,9 +2945,9 @@ 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;
}

3
mm/show_mem.c
View file

@ -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)));
}

29
mm/vmscan.c
View file

@ -506,7 +506,7 @@ 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;
/*
@ -6437,7 +6437,7 @@ 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) {
@ -6846,7 +6846,7 @@ 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)) {
@ -7111,8 +7111,11 @@ restart:
* 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);
@ -7371,7 +7374,7 @@ 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))) {
/*
@ -7391,9 +7394,11 @@ 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);
}
/*
@ -7406,7 +7411,13 @@ 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

2
mm/vmstat.c
View file

@ -1840,7 +1840,7 @@ 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);