The patch titled
Subject: hung_task: add detect count for hung tasks
has been added to the -mm mm-nonmm-unstable branch. Its filename is
hung_task-add-detect-count-for-hung-tasks.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hung_task-add-detect-count-for-hung-tasks.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lance Yang <ioworker0@xxxxxxxxx>
Subject: hung_task: add detect count for hung tasks
Date: Sun, 27 Oct 2024 20:07:46 +0800
Patch series "add detect count for hung tasks", v2.
This patchset adds a counter, hung_task_detect_count, to track the number
of times hung tasks are detected.
IHMO, hung tasks are a critical metric. Currently, we detect them by
periodically parsing dmesg. However, this method isn't as user-friendly
as using a counter.
Sometimes, a short-lived issue with NIC or hard drive can quickly decrease
the hung_task_warnings to zero. Without warnings, we must directly access
the node to ensure that there are no more hung tasks and that the system
has recovered. After all, load average alone cannot provide a clear
picture.
Once this counter is in place, in a high-density deployment pattern, we
plan to set hung_task_timeout_secs to a lower number to improve stability,
even though this might result in false positives. And then we can set a
time-based threshold: if hung tasks last beyond this duration, we will
automatically migrate containers to other nodes. Based on past
experience, this approach could help avoid many production disruptions.
Moreover, just like other important events such as OOM that already have
counters, having a dedicated counter for hung tasks makes sense ;)
This patch (of 2):
This commit adds a counter, hung_task_detect_count, to track the number of
times hung tasks are detected.
IHMO, hung tasks are a critical metric. Currently, we detect them by
periodically parsing dmesg. However, this method isn't as user-friendly as
using a counter.
Sometimes, a short-lived issue with NIC or hard drive can quickly decrease
the hung_task_warnings to zero. Without warnings, we must directly access
the node to ensure that there are no more hung tasks and that the system
has recovered. After all, load average alone cannot provide a clear
picture.
Once this counter is in place, in a high-density deployment pattern, we
plan to set hung_task_timeout_secs to a lower number to improve stability,
even though this might result in false positives. And then we can set a
time-based threshold: if hung tasks last beyond this duration, we will
automatically migrate containers to other nodes. Based on past experience,
this approach could help avoid many production disruptions.
Moreover, just like other important events such as OOM that already have
counters, having a dedicated counter for hung tasks makes sense.
Link: https://lkml.kernel.org/r/20241027120747.42833-1-ioworker0@xxxxxxxxx
Link: https://lkml.kernel.org/r/20241027120747.42833-2-ioworker0@xxxxxxxxx
Signed-off-by: Mingzhe Yang <mingzhe.yang@xxxxxx>
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Bang Li <libang.li@xxxxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Huang Cun <cunhuang@xxxxxxxxxxx>
Cc: Joel Granados <j.granados@xxxxxxxxxxx>
Cc: Joel Granados <joel.granados@xxxxxxxxxx>
Cc: John Siddle <jsiddle@xxxxxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Thomas WeiÃ?schuh <linux@xxxxxxxxxxxxxx>
Cc: Yongliang Gao <leonylgao@xxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/hung_task.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
--- a/kernel/hung_task.c~hung_task-add-detect-count-for-hung-tasks
+++ a/kernel/hung_task.c
@@ -31,6 +31,11 @@
static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
/*
+ * Total number of tasks detected as hung since boot:
+ */
+static unsigned long __read_mostly sysctl_hung_task_detect_count;
+
+/*
* Limit number of tasks checked in a batch.
*
* This value controls the preemptibility of khungtaskd since preemption
@@ -115,6 +120,12 @@ static void check_hung_task(struct task_
if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
return;
+ /*
+ * This counter tracks the total number of tasks detected as hung
+ * since boot.
+ */
+ sysctl_hung_task_detect_count++;
+
trace_sched_process_hang(t);
if (sysctl_hung_task_panic) {
@@ -314,6 +325,13 @@ static struct ctl_table hung_task_sysctl
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_NEG_ONE,
},
+ {
+ .procname = "hung_task_detect_count",
+ .data = &sysctl_hung_task_detect_count,
+ .maxlen = sizeof(unsigned long),
+ .mode = 0444,
+ .proc_handler = proc_dointvec,
+ },
};
static void __init hung_task_sysctl_init(void)
_
Patches currently in -mm which might be from ioworker0@xxxxxxxxx are
hung_task-add-detect-count-for-hung-tasks.patch
hung_task-add-docs-for-hung_task_detect_count.patch
