From: Roman Gushchin <guro@xxxxxx> Subject: mm: kmem: make memcg_kmem_enabled() irreversible Historically the kernel memory accounting was an opt-in feature, which could be enabled for individual cgroups. But now it's not true, and it's on by default both on cgroup v1 and cgroup v2. And as long as a user has at least one non-root memory cgroup, the kernel memory accounting is on. So in most setups it's either always on (if memory cgroups are in use and kmem accounting is not disabled), either always off (otherwise). memcg_kmem_enabled() is used in many places to guard the kernel memory accounting code. If memcg_kmem_enabled() can reverse from returning true to returning false (as now), we can't rely on it on release paths and have to check if it was on before. If we'll make memcg_kmem_enabled() irreversible (always returning true after returning it for the first time), it'll make the general logic more simple and robust. It also will allow to guard some checks which otherwise would stay unguarded. Link: http://lkml.kernel.org/r/20200702180926.1330769-1-guro@xxxxxx Signed-off-by: Roman Gushchin <guro@xxxxxx> Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) --- a/mm/memcontrol.c~mm-kmem-make-memcg_kmem_enabled-irreversible +++ a/mm/memcontrol.c @@ -3416,7 +3416,8 @@ static int memcg_online_kmem(struct mem_ if (memcg_id < 0) return memcg_id; - static_branch_inc(&memcg_kmem_enabled_key); + static_branch_enable(&memcg_kmem_enabled_key); + /* * A memory cgroup is considered kmem-online as soon as it gets * kmemcg_id. Setting the id after enabling static branching will @@ -3486,11 +3487,6 @@ static void memcg_free_kmem(struct mem_c /* css_alloc() failed, offlining didn't happen */ if (unlikely(memcg->kmem_state == KMEM_ONLINE)) memcg_offline_kmem(memcg); - - if (memcg->kmem_state == KMEM_ALLOCATED) { - WARN_ON(!list_empty(&memcg->kmem_caches)); - static_branch_dec(&memcg_kmem_enabled_key); - } } #else static int memcg_online_kmem(struct mem_cgroup *memcg) _
