lkml.org 
[lkml]   [2018]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer.
From
Date
On 2018/06/27 8:50, Paul E. McKenney wrote:
> On Wed, Jun 27, 2018 at 05:10:48AM +0900, Tetsuo Handa wrote:
>> As far as I can see,
>>
>> - atomic_set(&oom_callback_count, 1);
>> + atomic_inc(&oom_callback_count);
>>
>> should be sufficient.
>
> I don't see how that helps. For example, suppose that two tasks
> invoked rcu_oom_notify() at about the same time. Then they could
> both see oom_callback_count equal to zero, both atomically increment
> oom_callback_count, then both do the IPI invoking rcu_oom_notify_cpu()
> on each online CPU.
>
> So far, so good. But rcu_oom_notify_cpu() enqueues a per-CPU RCU
> callback, and enqueuing the same callback twice in quick succession
> would fatally tangle RCU's callback lists.
>
> What am I missing here?
>
> Thanx, Paul

You are pointing out that "number of rsp->call() is called" > "number of
rcu_oom_callback() is called" can happen if concurrently called, aren't you?
Then, you are not missing anything. You will need to use something equivalent
to oom_lock even if you can convert rcu_oom_notify() to use shrinkers.

\
 
 \ /
  Last update: 2018-06-27 12:53    [W:0.104 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site