On 14.08.2015 20:03, Vladimir Davydov wrote:
> If an oom victim process has a low prio (nice or via cpu cgroup), it may
> take it very long to complete, which is bad, because the system cannot
> make progress until it dies. To avoid that, this patch makes oom killer
> set victim task prio to the highest possible.
>
> It might be worth submitting this patch upstream. I will probably try.
>
> Signed-off-by: Vladimir Davydov <[email protected]>
> ---
> mm/oom_kill.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 0e6f7535a565..ca765a82fa1a 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -294,6 +294,15 @@ enum oom_scan_t oom_scan_process_thread(struct
> task_struct *task,
> return OOM_SCAN_OK;
> }
>
> +static void boost_dying_task(struct task_struct *p)
> +{
> + /*
> + * Set the dying task scheduling priority to the highest possible so
> + * that it will die quickly irrespective of its scheduling policy.
> + */
> + sched_boost_task(p, 0);
> +}
> +
> /*
> * Simple selection loop. We chose the process with the highest
> * number of 'points'.
> @@ -321,6 +330,7 @@ static struct task_struct *select_bad_process(unsigned
> int *ppoints,
> case OOM_SCAN_CONTINUE:
> continue;
> case OOM_SCAN_ABORT:
> + boost_dying_task(p);
This is potential livelock as you are holding at least try_set_zonelist_oom()
bits locked
and concurrent thread may use GFP_NOFAIL in __alloc_pages_slowpath(). This case
it will be
looping forever.
Furthermore, you manually do schedule_timeout_killable() in out_of_memory(), so
this problem
is a problem of !PREEMPTIBLE kernel too.
You mustn't leave processor before you're cleared the bits.
> rcu_read_unlock();
> return ERR_PTR(-1UL);
> case OOM_SCAN_OK:
> @@ -426,8 +436,7 @@ void oom_kill_process(struct task_struct *p, gfp_t
> gfp_mask, int order,
> */
> if (p->flags & PF_EXITING) {
> set_tsk_thread_flag(p, TIF_MEMDIE);
> - put_task_struct(p);
> - return;
> + goto out;
> }
>
> if (__ratelimit(&oom_rs))
> @@ -512,6 +521,9 @@ void oom_kill_process(struct task_struct *p, gfp_t
> gfp_mask, int order,
> set_tsk_thread_flag(victim, TIF_MEMDIE);
> do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
> mem_cgroup_note_oom_kill(memcg, victim);
> +out:
> + if (!memcg)
> + boost_dying_task(victim);
> put_task_struct(victim);
> }
> #undef K
> @@ -638,6 +650,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t
> gfp_mask,
> */
> if (fatal_signal_pending(current) || current->flags & PF_EXITING) {
> set_thread_flag(TIF_MEMDIE);
> + boost_dying_task(current);
> return;
> }
>
>
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