Re: [PATCH 1/2] mm, oom: introduce oom reaper

[Andrew Morton]

On Tue, 15 Dec 2015 19:36:15 +0100 Michal Hocko <mho...@kernel.org> wrote:

> This patch reduces the probability of such a lockup by introducing a
> specialized kernel thread (oom_reaper) 

CONFIG_MMU=n:

slub.c:(.text+0x4184): undefined reference to `tlb_gather_mmu'
slub.c:(.text+0x41bc): undefined reference to `unmap_page_range'
slub.c:(.text+0x41d8): undefined reference to `tlb_finish_mmu'

I did the below so I can get an mmotm out the door, but hopefully
there's a cleaner way.

--- a/mm/oom_kill.c~mm-oom-introduce-oom-reaper-fix-3
+++ a/mm/oom_kill.c
@@ -415,6 +415,7 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_victi
 
 bool oom_killer_disabled __read_mostly;
 
+#ifdef CONFIG_MMU
 /*
  * OOM Reaper kernel thread which tries to reap the memory used by the OOM
  * victim (if that is possible) to help the OOM killer to move on.
@@ -517,6 +518,27 @@ static void wake_oom_reaper(struct mm_st
                mmdrop(mm);
 }
 
+static int __init oom_init(void)
+{
+       oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
+       if (IS_ERR(oom_reaper_th)) {
+               pr_err("Unable to start OOM reaper %ld. Continuing 
regardless\n",
+                               PTR_ERR(oom_reaper_th));
+               oom_reaper_th = NULL;
+       } else {
+               struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+
+               /*
+                * Make sure our oom reaper thread will get scheduled when
+                * ASAP and that it won't get preempted by malicious userspace.
+                */
+               sched_setscheduler(oom_reaper_th, SCHED_FIFO, &param);
+       }
+       return 0;
+}
+module_init(oom_init)
+#endif
+
 /**
  * mark_oom_victim - mark the given task as OOM victim
  * @tsk: task to mark
@@ -626,7 +648,9 @@ void oom_kill_process(struct oom_control
        unsigned int victim_points = 0;
        static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
                                              DEFAULT_RATELIMIT_BURST);
+#ifdef CONFIG_MMU
        bool can_oom_reap = true;
+#endif
 
        /*
         * If the task is already exiting, don't alarm the sysadmin or kill
@@ -719,6 +743,7 @@ void oom_kill_process(struct oom_control
                        continue;
                if (is_global_init(p))
                        continue;
+#ifdef CONFIG_MMU
                if (unlikely(p->flags & PF_KTHREAD) ||
                    p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
                        /*
@@ -729,13 +754,16 @@ void oom_kill_process(struct oom_control
                        can_oom_reap = false;
                        continue;
                }
-
+#endif
                do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
        }
        rcu_read_unlock();
 
+#ifdef CONFIG_MMU
        if (can_oom_reap)
                wake_oom_reaper(mm);
+#endif
+
        mmdrop(mm);
        put_task_struct(victim);
 }
@@ -887,23 +915,3 @@ void pagefault_out_of_memory(void)
 
        mutex_unlock(&oom_lock);
 }
-
-static int __init oom_init(void)
-{
-       oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
-       if (IS_ERR(oom_reaper_th)) {
-               pr_err("Unable to start OOM reaper %ld. Continuing 
regardless\n",
-                               PTR_ERR(oom_reaper_th));
-               oom_reaper_th = NULL;
-       } else {
-               struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
-
-               /*
-                * Make sure our oom reaper thread will get scheduled when
-                * ASAP and that it won't get preempted by malicious userspace.
-                */
-               sched_setscheduler(oom_reaper_th, SCHED_FIFO, &param);
-       }
-       return 0;
-}
-module_init(oom_init)
_

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