Re: [PATCH] oom_reaper: switch to struct list_head for reap queue

[Aleksa Sarai]

> > > This is an extra pointer to task_struct and more lines of code to
> > > accomplish the same thing. Why would we want to do that?
> >
> > I don't think it's more "actual" lines of code (I think the wrapping is
> > inflating the line number count),
>
> I too think it doesn't make sense to blow task_struct and the generated code.
> And to me this patch doesn't make the source code more clean.
>
> > but switching it means that it's more in
> > line with other queues in the kernel (it took me a bit to figure out what
> > was going on with oom_reaper_list beforehand).
>
> perhaps you can turn oom_reaper_list into llist_head then. This will also
> allow to remove oom_reaper_lock. Not sure this makes sense too.

Actually, I just noticed that the original implementation is a stack not 
a queue. So the reaper will always reap the *most recent* task to get 
OOMed as opposed to the least recent. Since select_bad_process() will 
always pick worse processes first, this means that the reaper will reap 
"less bad" processes (lower oom score) before it reaps worse ones 
(higher oom score).

While it's not a /huge/ deal (N is going to be small in most OOM cases), 
is this something that we should consider?

RE: llist_head, the problem with that is that appending to the end is an 
O(n) operation. Though, as I said, n is not going to be very large in 
most cases.

--
Aleksa Sarai
Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/