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Subject[RFC PATCH] mm/oom_kill: show oom eligibility when displaying the current memory state of all tasks
Date
At the present time, when showing potential OOM victims, we do not
exclude tasks which already 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 misleading, to the reader of the
OOM report. 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 i.e. is not eligible.

This patch provides a clear indication with regard to the OOM
eligibility of each displayed task.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
mm/oom_kill.c | 31 +++++++++++++++++++++++++++----
1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index eefd3f5fde46..70781d681a6e 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 * is_task_oom_eligible(struct task_struct *p)
+{
+ long adj;
+
+ adj = (long)p->signal->oom_score_adj;
+ if (adj == OOM_SCORE_ADJ_MIN)
+ return "no: oom score";
+ else if (test_bit(MMF_OOM_SKIP, &p->mm->flags)
+ return "no: oom reaped";
+ else if (in_vfork(p))
+ return "no: in vfork";
+ else
+ return "yes";
+}
+
/* 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 %-15s %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 eligible 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 eligible? name\n");

if (is_memcg_oom(oc))
mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
--
2.26.3
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