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Date: Mon, 1 Aug 2022 21:55:31 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Yafang Shao <laoar.shao@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
kafai@...com, songliubraving@...com, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
haoluo@...gle.com, jolsa@...nel.org, hannes@...xchg.org,
mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
songmuchun@...edance.com, akpm@...ux-foundation.org,
netdev@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH bpf-next 15/15] bpf: Introduce selectable memcg for
bpf map
On Fri, Jul 29, 2022 at 03:23:16PM +0000, Yafang Shao wrote:
> A new member memcg_fd is introduced into bpf attr of BPF_MAP_CREATE
> command, which is the fd of an opened cgroup directory. In this cgroup,
> the memory subsystem must be enabled. This value is valid only when
> BPF_F_SELECTABLE_MEMCG is set in map_flags. Once the kernel get the
> memory cgroup from this fd, it will set this memcg into bpf map, then
> all the subsequent memory allocation of this map will be charge to the
> memcg.
>
> The map creation paths in libbpf are also changed consequently.
>
> Currently it is only supported for cgroup2 directory.
>
> The usage of this new member as follows,
> struct bpf_map_create_opts map_opts = {
> .sz = sizeof(map_opts),
> .map_flags = BPF_F_SELECTABLE_MEMCG,
> };
> int memcg_fd, int map_fd;
> int key, value;
>
> memcg_fd = open("/cgroup2", O_DIRECTORY);
> if (memcg_fd < 0) {
> perror("memcg dir open");
> return -1;
> }
>
> map_opts.memcg_fd = memcg_fd;
> map_fd = bpf_map_create(BPF_MAP_TYPE_HASH, "map_for_memcg",
> sizeof(key), sizeof(value),
> 1024, &map_opts);
> if (map_fd <= 0) {
> perror("map create");
> return -1;
> }
Overall the api extension makes sense.
The flexibility of selecting memcg is useful.
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
> include/uapi/linux/bpf.h | 2 ++
> kernel/bpf/syscall.c | 47 ++++++++++++++++++++++++++--------
> tools/include/uapi/linux/bpf.h | 2 ++
> tools/lib/bpf/bpf.c | 1 +
> tools/lib/bpf/bpf.h | 3 ++-
> tools/lib/bpf/libbpf.c | 2 ++
> 6 files changed, 46 insertions(+), 11 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d5fc1ea70b59..a6e02c8be924 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1296,6 +1296,8 @@ union bpf_attr {
> * struct stored as the
> * map value
> */
> + __s32 memcg_fd; /* selectable memcg */
> + __s32 :32; /* hole */
new fields cannot be inserted in the middle of uapi struct.
> /* Any per-map-type extra fields
> *
> * BPF_MAP_TYPE_BLOOM_FILTER - the lowest 4 bits indicate the
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 6401cc417fa9..9900e2b87315 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -402,14 +402,30 @@ 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)
> +static int bpf_map_save_memcg(struct bpf_map *map, union bpf_attr *attr)
> {
> - /* 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();
> + struct obj_cgroup *objcg;
> + struct cgroup *cgrp;
> +
> + if (attr->map_flags & BPF_F_SELECTABLE_MEMCG) {
The flag is unnecessary. Just add memcg_fd to the end of attr and use != 0
as a condition that it should be used instead of get_obj_cgroup_from_current().
There are other parts of bpf uapi that have similar fd handling logic.
> + cgrp = cgroup_get_from_fd(attr->memcg_fd);
> + if (IS_ERR(cgrp))
> + return -EINVAL;
> +
> + objcg = get_obj_cgroup_from_cgroup(cgrp);
> + if (IS_ERR(objcg))
> + return PTR_ERR(objcg);
> + } else {
> + /* 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.
> + */
> + objcg = get_obj_cgroup_from_current();
> + }
> +
> + map->objcg = objcg;
> + return 0;
> }
>
> static void bpf_map_release_memcg(struct bpf_map *map)
> @@ -485,8 +501,9 @@ void __percpu *bpf_map_alloc_percpu(const struct bpf_map *map, size_t size,
> }
>
> #else
> -static void bpf_map_save_memcg(struct bpf_map *map)
> +static int bpf_map_save_memcg(struct bpf_map *map, union bpf_attr *attr)
> {
> + return 0;
> }
>
> static void bpf_map_release_memcg(struct bpf_map *map)
> @@ -530,13 +547,18 @@ void *bpf_map_container_alloc(union bpf_attr *attr, u64 size, int numa_node)
High level uapi struct should not be passed into low level helper like this.
Pls pass memcg_fd instead.
> {
> struct bpf_map *map;
> void *container;
> + int ret;
>
> container = __bpf_map_area_alloc(size, numa_node, false);
> if (!container)
> return ERR_PTR(-ENOMEM);
>
> map = (struct bpf_map *)container;
> - bpf_map_save_memcg(map);
> + ret = bpf_map_save_memcg(map, attr);
> + if (ret) {
> + bpf_map_area_free(container);
> + return ERR_PTR(ret);
> + }
>
> return container;
> }
> @@ -547,6 +569,7 @@ void *bpf_map_container_mmapable_alloc(union bpf_attr *attr, u64 size,
> struct bpf_map *map;
> void *container;
> void *ptr;
> + int ret;
>
> /* kmalloc'ed memory can't be mmap'ed, use explicit vmalloc */
> ptr = __bpf_map_area_alloc(size, numa_node, true);
> @@ -555,7 +578,11 @@ void *bpf_map_container_mmapable_alloc(union bpf_attr *attr, u64 size,
>
> container = ptr + align - offset;
> map = (struct bpf_map *)container;
> - bpf_map_save_memcg(map);
> + ret = bpf_map_save_memcg(map, attr);
> + if (ret) {
> + bpf_map_area_free(ptr);
> + return ERR_PTR(ret);
> + }
>
> return ptr;
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index d5fc1ea70b59..a6e02c8be924 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -1296,6 +1296,8 @@ union bpf_attr {
> * struct stored as the
> * map value
> */
> + __s32 memcg_fd; /* selectable memcg */
> + __s32 :32; /* hole */
> /* Any per-map-type extra fields
> *
> * BPF_MAP_TYPE_BLOOM_FILTER - the lowest 4 bits indicate the
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 5eb0df90eb2b..662ce5808386 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -199,6 +199,7 @@ int bpf_map_create(enum bpf_map_type map_type,
> attr.map_extra = OPTS_GET(opts, map_extra, 0);
> attr.numa_node = OPTS_GET(opts, numa_node, 0);
> attr.map_ifindex = OPTS_GET(opts, map_ifindex, 0);
> + attr.memcg_fd = OPTS_GET(opts, memcg_fd, 0);
>
> fd = sys_bpf_fd(BPF_MAP_CREATE, &attr, attr_sz);
> return libbpf_err_errno(fd);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 88a7cc4bd76f..481aad49422b 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -51,8 +51,9 @@ struct bpf_map_create_opts {
>
> __u32 numa_node;
> __u32 map_ifindex;
> + __u32 memcg_fd;
> };
> -#define bpf_map_create_opts__last_field map_ifindex
> +#define bpf_map_create_opts__last_field memcg_fd
>
> LIBBPF_API int bpf_map_create(enum bpf_map_type map_type,
> const char *map_name,
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 50d41815f431..86916d550031 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -505,6 +505,7 @@ struct bpf_map {
> bool pinned;
> bool reused;
> bool autocreate;
> + __s32 memcg_fd;
> __u64 map_extra;
> };
>
> @@ -4928,6 +4929,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
> create_attr.map_ifindex = map->map_ifindex;
> create_attr.map_flags = def->map_flags;
> create_attr.numa_node = map->numa_node;
> + create_attr.memcg_fd = map->memcg_fd;
> create_attr.map_extra = map->map_extra;
>
> if (bpf_map__is_struct_ops(map))
> --
> 2.17.1
>
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