[PATCH 5/6] mm,oom: Re-enable OOM killer using timers.

[Tetsuo Handa]

>From 6f07b71c97766ec111d26c3424bded465ca48195 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 17 Feb 2016 16:37:01 +0900
Subject: [PATCH 5/6] mm,oom: Re-enable OOM killer using timers.

We are trying to reduce the possibility of hitting OOM livelock by
introducing the OOM reaper, but there are situations where the OOM reaper
cannot reap the victim's memory. We want to introduce the OOM reaper as
simple as possible and make the OOM reaper better via incremental
development.

This patch adds a timer for handling corner cases where a TIF_MEMDIE
thread got stuck by reasons not handled by the initial version of the
OOM reaper. Since "mm,oom: exclude TIF_MEMDIE processes from candidates."
made sure that we won't choose the same OOM victim forever and this patch
makes sure that the kernel automatically presses SysRq-f upon OOM stalls,
we will not OOM stall forever as long as the OOM killer is called.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 mm/oom_kill.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ebc6764..fba2c62 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -45,6 +45,11 @@ int sysctl_oom_dump_tasks = 1;
 
 DEFINE_MUTEX(oom_lock);
 
+static void oomkiller_reset(unsigned long arg)
+{
+}
+static DEFINE_TIMER(oomkiller_victim_wait_timer, oomkiller_reset, 0, 0);
+
 #ifdef CONFIG_NUMA
 /**
  * has_intersects_mems_allowed() - check task eligiblity for kill
@@ -299,7 +304,8 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
 	 */
 	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
 		if (!is_sysrq_oom(oc))
-			return OOM_SCAN_ABORT;
+			return timer_pending(&oomkiller_victim_wait_timer) ?
+				OOM_SCAN_ABORT : OOM_SCAN_CONTINUE;
 	}
 	if (!task->mm)
 		return OOM_SCAN_CONTINUE;
@@ -452,6 +458,8 @@ void mark_oom_victim(struct task_struct *tsk)
 	 */
 	__thaw_task(tsk);
 	atomic_inc(&oom_victims);
+	/* Make sure that we won't wait for this task forever. */
+	mod_timer(&oomkiller_victim_wait_timer, jiffies + 5 * HZ);
 }
 
 /**
-- 
1.8.3.1