On Wed, Jul 17, 2019 at 10:45 AM Yang Shi yang.shi@linux.alibaba.com 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 shakeelb@google.com Cc: Vladimir Davydov vdavydov.dev@gmail.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@suse.com Cc: Kirill Tkhai ktkhai@virtuozzo.com Cc: Roman Gushchin guro@fb.com Cc: Hugh Dickins hughd@google.com Cc: Qian Cai cai@lca.pw Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: stable@vger.kernel.org 4.19+ Signed-off-by: Yang Shi yang.shi@linux.alibaba.com
Reviewed-by: Shakeel Butt shakeelb@google.com
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