On 2020/07/14 11:58, Yafang Shao wrote:
> On Tue, Jul 14, 2020 at 10:42 AM Tetsuo Handa
> <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>>
>> On 2020/07/14 11:13, Yafang Shao wrote:
>>> But it seems the proposal that using trylock in
>>> mem_cgroup_out_of_memory() should be better?
>>> The trylock could also solve the problem that different processes are
>>> doing oom at the same time.
>>
>> I think trylock is worse. The trylock needlessly wastes CPU time which could
>> have been utilized by the OOM killer/reaper for reclaiming memory.
>
> If it may wastes the CPU time, we can shed it out for 1 second like
> what it does in __alloc_pages_may_oom():
>
> __alloc_pages_may_oom
> if (!mutex_trylock(&oom_lock)) {
> schedule_timeout_uninterruptible(1); // to avoid wasting CPU time
1 second is HZ. 1 means 1 millisecond if CONFIG_HZ=1000. :-)
> return;
> }
>
> But I find that we doesn't sched it out in pagefault path,
>
> pagefault_out_of_memory
> if (!mutex_trylock(&oom_lock))
> return;
>
> I haven't thought deeply what the difference is ...
David Rientjes is proposing it for avoiding soft lockup, and Michal Hocko is refusing it.
How to give the OOM killer/reaper enough CPU time for reclaiming memory is a dogfight. :-(
https://lkml.kernel.org/r/alpine.DEB.2.21.2003181458100.70237@xxxxxxxxxxxxxxxxxxxxxxxxx
