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.
