On Tue, 21 Aug 2018, Michal Hocko wrote:

quoted

Ok, so it appears you're suggesting a per-mm counter of oom reaper retries 
and once it reaches a certain threshold, either give up and set 
MMF_OOM_SKIP or declare that exit_mmap() is responsible for it.  That's 
fine, but obviously I'll be suggesting that the threshold is rather large.  
So if I adjust my patch to be a retry counter rather than timestamp, do 
you have any other reservations?

It absolutely has to be an internal thing without any user API to be
set. Also I still haven't heard any specific argument why would oom
reaper need to do per-task attempt and loop over all victims on the
list. Maybe you have some examples though.

It would be per-mm in this case, the task itself is no longer important 
other than printing to the kernel log.  I think we could simply print that 
the oom reaper has reaped mm->owner.

The oom reaper would need to loop over the per-mm list because the retry 
counter is going to have a high threshold so that processes have the 
ability to free their memory before the oom reaper declares it can no 
longer make forward progress.  We cannot stall trying to reap a single mm 
with a high retry threshold from a memcg hierarchy when another memcg 
hierarchy is also oom.  The ability for one victim to make forward 
progress can depend on a lock held by another oom memcg hierarchy where 
reaping would allow it to be dropped.