Re: [PATCH v2] mm, memcg: avoid oom if cgroup is not populated

[Michal Hocko <mhocko@kernel.org>]

On Tue 26-11-19 20:28:37, Yafang Shao wrote:
> There's one case that the processes in a memcg are all exit (due to OOM
> group or some other reasons), but the file page caches are still exist.
> These file page caches may be protected by memory.min so can't be
> reclaimed. If we can't success to restart the processes in this memcg or
> don't want to make this memcg offline, then we want to drop the file page
> caches.
> The advantage of droping this file caches is it can avoid the reclaimer
> (either kswapd or direct) scanning and reclaiming pages from all memcgs
> exist in this system, because currently the reclaimer will fairly reclaim
> pages from all memcgs if the system is under memory pressure.
> The possible method to drop these file page caches is setting the
> hard limit of this memcg to 0. Unfortunately this may invoke the OOM killer
> and generates lots of outputs, that should not happen.
> The OOM output is not expected by the admin if he or she wants to drop
> the cahes and knows there're no processes in this memcg.
> 
> If memcg is not populated, we should not invoke the OOM killer because
> there's nothing to kill. Next time when you start a new process and if the
> max is still bellow usage, the OOM killer will be invoked and your new
> process is killed, so we can cosider it as lazy OOM, that is we have been
> always doing in the kernel.
> 
> Fixes: b6e6edcf ("mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage")
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.com>

due to reasons explained repeatedly
Nacked-by: Michal Hocko <mhocko@suse.com>

And I really find it highly annoying that you keep ignoring the review
feedback.
-- 
Michal Hocko
SUSE Labs