On Thu 06-09-18 23:06:40, Tetsuo Handa wrote:
> On 2018/09/06 22:56, Michal Hocko wrote:
> > On Thu 06-09-18 22:40:24, Tetsuo Handa wrote:
> >> On 2018/09/06 21:05, Michal Hocko wrote:
> >>>> If you are too busy, please show "the point of no-blocking" using source code
> >>>> instead. If such "the point of no-blocking" really exists, it can be executed
> >>>> by allocating threads.
> >>>
> >>> I would have to study this much deeper but I _suspect_ that we are not
> >>> taking any blocking locks right after we return from unmap_vmas. In
> >>> other words the place we used to have synchronization with the
> >>> oom_reaper in the past.
> >>
> >> See commit 97b1255cb27c551d ("mm,oom_reaper: check for MMF_OOM_SKIP before
> >> complaining"). Since this dependency is inode-based (i.e. irrelevant with
> >> OOM victims), waiting for this lock can livelock.
> >>
> >> So, where is safe "the point of no-blocking" ?
> >
> > Ohh, right unlink_file_vma and its i_mmap_rwsem lock. As I've said I
> > have to think about that some more. Maybe we can split those into two parts.
> >
>
> Meanwhile, I'd really like to use timeout based back off. Like I wrote at
> http://lkml.kernel.org/r/201809060703.w8673Kbs076435@xxxxxxxxxxxxxxxxxxx ,
> we need to wait for some period after all.
>
> We can replace timeout based back off after we got safe "the point of no-blocking" .
Why don't you invest your time in the long term solution rather than
playing with something that doesn't solve anything just papers over the
issue?
--
Michal Hocko
SUSE Labs
