On Tue, Jul 12, 2022 at 2:49 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Mon, Jul 11, 2022 at 9:28 AM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote:
> >
> > The memory consumed by a mpf map is always accounted to the memory
> > cgroup of the process which created the map. The map can outlive
> > the memory cgroup if it's used by processes in other cgroups or
> > is pinned on bpffs. In this case the map pins the original cgroup
> > in the dying state.
> >
> > For other types of objects (slab objects, non-slab kernel allocations,
> > percpu objects and recently LRU pages) there is a reparenting process
> > implemented: on cgroup offlining charged objects are getting
> > reassigned to the parent cgroup. Because all charges and statistics
> > are fully recursive it's a fairly cheap operation.
> >
> > For efficiency and consistency with other types of objects, let's do
> > the same for bpf maps. Fortunately thanks to the objcg API, the
> > required changes are minimal.
> >
> > Please, note that individual allocations (slabs, percpu and large
> > kmallocs) already have the reparenting mechanism. This commit adds
> > it to the saved map->memcg pointer by replacing it to map->objcg.
> > Because dying cgroups are not visible for a user and all charges are
> > recursive, this commit doesn't bring any behavior changes for a user.
> >
> > v2:
> > added a missing const qualifier
> >
> > Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > ---
> > include/linux/bpf.h | 2 +-
> > kernel/bpf/syscall.c | 35 +++++++++++++++++++++++++++--------
> > 2 files changed, 28 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 2b21f2a3452f..85a4db3e0536 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -221,7 +221,7 @@ struct bpf_map {
> > u32 btf_vmlinux_value_type_id;
> > struct btf *btf;
> > #ifdef CONFIG_MEMCG_KMEM
> > - struct mem_cgroup *memcg;
> > + struct obj_cgroup *objcg;
> > #endif
> > char name[BPF_OBJ_NAME_LEN];
> > struct bpf_map_off_arr *off_arr;
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index ab688d85b2c6..ef60dbc21b17 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -419,35 +419,52 @@ void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock)
> > #ifdef CONFIG_MEMCG_KMEM
> > static void bpf_map_save_memcg(struct bpf_map *map)
> > {
> > - map->memcg = get_mem_cgroup_from_mm(current->mm);
> > + /* Currently if a map is created by a process belonging to the root
> > + * memory cgroup, get_obj_cgroup_from_current() will return NULL.
> > + * So we have to check map->objcg for being NULL each time it's
> > + * being used.
> > + */
> > + map->objcg = get_obj_cgroup_from_current();
> > }
> >
> > static void bpf_map_release_memcg(struct bpf_map *map)
> > {
> > - mem_cgroup_put(map->memcg);
> > + if (map->objcg)
> > + obj_cgroup_put(map->objcg);
> > +}
> > +
> > +static struct mem_cgroup *bpf_map_get_memcg(const struct bpf_map *map) {
> > + if (map->objcg)
> > + return get_mem_cgroup_from_objcg(map->objcg);
> > +
> > + return root_mem_cgroup;
> > }
> >
> > void *bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags,
> > int node)
> > {
> > - struct mem_cgroup *old_memcg;
> > + struct mem_cgroup *memcg, *old_memcg;
> > void *ptr;
> >
> > - old_memcg = set_active_memcg(map->memcg);
> > + memcg = bpf_map_get_memcg(map);
> > + old_memcg = set_active_memcg(memcg);
> > ptr = kmalloc_node(size, flags | __GFP_ACCOUNT, node);
> > set_active_memcg(old_memcg);
> > + mem_cgroup_put(memcg);
>
> Here we might css_put root_mem_cgroup.
> Should we css_get it when returning or
> it's marked as CSS_NO_REF ?
> But mem_cgroup_alloc() doesn't seem to be doing that marking.
> I'm lost at that code.
CSS_NO_REF is set for root_mem_cgroup in cgroup_init_subsys().
