On Mon, 10 Sep 2018, Roman Gushchin wrote: > The memcg OOM killer is never invoked due to a failed high-order > allocation, however the MEMCG_OOM event can be easily raised. > > Under some memory pressure it can happen easily because of a > concurrent allocation. Let's look at try_charge(). Even if we were > able to reclaim enough memory, this check can fail due to a race > with another allocation: > > if (mem_cgroup_margin(mem_over_limit) >= nr_pages) > goto retry; > > For regular pages the following condition will save us from triggering > the OOM: > > if (nr_reclaimed && nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER)) > goto retry; > > But for high-order allocation this condition will intentionally fail. > The reason behind is that we'll likely fall to regular pages anyway, > so it's ok and even preferred to return ENOMEM. > > In this case the idea of raising the MEMCG_OOM event looks dubious. > > Fix this by moving MEMCG_OOM raising to mem_cgroup_oom() after > allocation order check, so that the event won't be raised for high > order allocations. > > Signed-off-by: Roman Gushchin <guro@xxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
