On Wed 01-07-20 11:45:52, Roman Gushchin wrote: [...] > >From c97afecd32c0db5e024be9ba72f43d22974f5bcd Mon Sep 17 00:00:00 2001 > From: Roman Gushchin <guro@xxxxxx> > Date: Wed, 1 Jul 2020 11:05:32 -0700 > Subject: [PATCH] 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. > > Signed-off-by: Roman Gushchin <guro@xxxxxx> > --- > mm/memcontrol.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 50ae77f3985e..2d018a51c941 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3582,7 +3582,8 @@ static int memcg_online_kmem(struct mem_cgroup *memcg) > objcg->memcg = memcg; > rcu_assign_pointer(memcg->objcg, objcg); > > - static_branch_inc(&memcg_kmem_enabled_key); > + if (!memcg_kmem_enabled()) > + static_branch_inc(&memcg_kmem_enabled_key); Wouldn't be static_branch_enable() more readable? > /* > * A memory cgroup is considered kmem-online as soon as it gets > * kmemcg_id. Setting the id after enabling static branching will > @@ -3643,9 +3644,6 @@ static void memcg_free_kmem(struct mem_cgroup *memcg) > /* css_alloc() failed, offlining didn't happen */ > if (unlikely(memcg->kmem_state == KMEM_ONLINE)) > memcg_offline_kmem(memcg); > - > - if (memcg->kmem_state == KMEM_ALLOCATED) > - static_branch_dec(&memcg_kmem_enabled_key); > } > #else > static int memcg_online_kmem(struct mem_cgroup *memcg) > -- > 2.26.2 -- Michal Hocko SUSE Labs
