Changes since v2:
- Use single character (e.g. 'R' for MMF_OOM_SKIP) as suggested
by Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
- Add new header to oom_dump_tasks documentation
- Provide further justification
The output generated by dump_tasks() can be helpful to determine why
there was an OOM condition and which rogue task potentially caused it.
Please note that this is only provided when sysctl oom_dump_tasks is
enabled.
At the present time, when showing potential OOM victims, we do not
exclude any task that are not OOM eligible e.g. those that have
MMF_OOM_SKIP set; it is possible that the last OOM killable victim was
already OOM killed, yet the OOM reaper failed to reclaim memory and set
MMF_OOM_SKIP. This can be confusing (or perhaps even be misleading) to the
viewer. Now, we already unconditionally display a task's oom_score_adj_min
value that can be set to OOM_SCORE_ADJ_MIN which is indicative of an
"unkillable" task.
This patch provides a clear indication with regard to the OOM ineligibility
(and why) of each displayed task with the addition of a new column namely
"oom_skipped". An example is provided below:
[ 5084.524970] [ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj oom_skipped name
[ 5084.526397] [660417] 0 660417 35869 683 167936 0 -1000 M conmon
[ 5084.526400] [660452] 0 660452 175834 472 86016 0 -998 pod
[ 5084.527460] [752415] 0 752415 35869 650 172032 0 -1000 M conmon
[ 5084.527462] [752575] 1001050000 752575 184205 11158 700416 0 999 npm
[ 5084.527467] [753606] 1001050000 753606 183380 46843 2134016 0 999 node
[ 5084.527581] Memory cgroup out of memory: Killed process 753606 (node) total-vm:733520kB, anon-rss:161228kB, file-rss:26144kB, shmem-rss:0kB, UID:1001050000
So, a single character 'M' is for OOM_SCORE_ADJ_MIN, 'R' MMF_OOM_SKIP and
'V' for in_vfork().
Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
---
Documentation/admin-guide/sysctl/vm.rst | 5 ++--
mm/oom_kill.c | 31 +++++++++++++++++++++----
2 files changed, 30 insertions(+), 6 deletions(-)
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 003d5cc3751b..4c79fa00ddb3 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -650,8 +650,9 @@ oom_dump_tasks
Enables a system-wide task dump (excluding kernel threads) to be produced
when the kernel performs an OOM-killing and includes such information as
pid, uid, tgid, vm size, rss, pgtables_bytes, swapents, oom_score_adj
-score, and name. This is helpful to determine why the OOM killer was
-invoked, to identify the rogue task that caused it, and to determine why
+score, oom eligibility status and name. This is helpful to determine why
+the OOM killer was invoked, to identify the rogue task that caused it, and
+to determine why
the OOM killer chose the task it did to kill.
If this is set to zero, this information is suppressed. On very
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c729a4c4a1ac..36daa6917b62 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -160,6 +160,27 @@ static inline bool is_sysrq_oom(struct oom_control *oc)
return oc->order == -1;
}
+/**
+ * is_task_eligible_oom - determine if and why a task cannot be OOM killed
+ * @tsk: task to check
+ *
+ * Needs to be called with task_lock().
+ */
+static const char * const is_task_oom_eligible(struct task_struct *p)
+{
+ long adj;
+
+ adj = (long)p->signal->oom_score_adj;
+ if (adj == OOM_SCORE_ADJ_MIN)
+ return "M";
+ else if (test_bit(MMF_OOM_SKIP, &p->mm->flags)
+ return "R";
+ else if (in_vfork(p))
+ return "V";
+ else
+ return "";
+}
+
/* return true if the task is not adequate as candidate victim task. */
static bool oom_unkillable_task(struct task_struct *p)
{
@@ -401,12 +422,13 @@ static int dump_task(struct task_struct *p, void *arg)
return 0;
}
- pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n",
+ pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %1s %s\n",
task->pid, from_kuid(&init_user_ns, task_uid(task)),
task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
mm_pgtables_bytes(task->mm),
get_mm_counter(task->mm, MM_SWAPENTS),
- task->signal->oom_score_adj, task->comm);
+ task->signal->oom_score_adj, is_task_oom_eligible(task),
+ task->comm);
task_unlock(task);
return 0;
@@ -420,12 +442,13 @@ static int dump_task(struct task_struct *p, void *arg)
* memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
* are not shown.
* State information includes task's pid, uid, tgid, vm size, rss,
- * pgtables_bytes, swapents, oom_score_adj value, and name.
+ * pgtables_bytes, swapents, oom_score_adj value, oom eligibility status
+ * and name.
*/
static void dump_tasks(struct oom_control *oc)
{
pr_info("Tasks state (memory values in pages):\n");
- pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n");
+ pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj oom_skipped name\n");
if (is_memcg_oom(oc))
mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
--
2.31.1
