On Wed, Jul 17, 2019 at 10:45 AM Yang Shi <[email protected]> wrote: > > Shakeel Butt reported premature oom on kernel with > "cgroup_disable=memory" since mem_cgroup_is_root() returns false even > though memcg is actually NULL. The drop_caches is also broken. > > It is because commit aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() > calls in shrink_node()") removed the !memcg check before > !mem_cgroup_is_root(). And, surprisingly root memcg is allocated even > though memory cgroup is disabled by kernel boot parameter. > > Add mem_cgroup_disabled() check to make reclaimer work as expected. > > Fixes: aeed1d325d42 ("mm/vmscan.c: generalize shrink_slab() calls in > shrink_node()") > Reported-by: Shakeel Butt <[email protected]> > Cc: Vladimir Davydov <[email protected]> > Cc: Johannes Weiner <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Kirill Tkhai <[email protected]> > Cc: Roman Gushchin <[email protected]> > Cc: Hugh Dickins <[email protected]> > Cc: Qian Cai <[email protected]> > Cc: Kirill A. Shutemov <[email protected]> > Cc: [email protected] 4.19+ > Signed-off-by: Yang Shi <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]> > --- > mm/vmscan.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f8e3dcd..c10dc02 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -684,7 +684,14 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, > unsigned long ret, freed = 0; > struct shrinker *shrinker; > > - if (!mem_cgroup_is_root(memcg)) > + /* > + * The root memcg might be allocated even though memcg is disabled > + * via "cgroup_disable=memory" boot parameter. This could make > + * mem_cgroup_is_root() return false, then just run memcg slab > + * shrink, but skip global shrink. This may result in premature > + * oom. > + */ > + if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) > return shrink_slab_memcg(gfp_mask, nid, memcg, priority); > > if (!down_read_trylock(&shrinker_rwsem)) > -- > 1.8.3.1 >
