Re: [PATCH bpf-next v2] bpf: increase supported cgroup storage value size

Yonghong Song
2021-07-26T00:37:37Z

On 7/23/21 4:54 PM, Stanislav Fomichev wrote:
> Current max cgroup storage value size is 4k (PAGE_SIZE). The other local
> storages accept up to 64k (BPF_LOCAL_STORAGE_MAX_VALUE_SIZE). Let's align
> max cgroup value size with the other storages.
>
> For percpu, the max is 32k (PCPU_MIN_UNIT_SIZE) because percpu
> allocator is not happy about larger values.
>
> netcnt test is extended to exercise those maximum values
> (non-percpu max size is close to, but not real max).
>
> v2:
> * cap max_value_size instead of BUILD_BUG_ON (Martin KaFai Lau)
>
> Cc: Martin KaFai Lau <kafai@fb.com>
> Signed-off-by: Stanislav Fomichev <sdf@google.com>
> ---
> kernel/bpf/local_storage.c | 11 +++++-
> tools/testing/selftests/bpf/netcnt_common.h | 38 +++++++++++++++----
> .../testing/selftests/bpf/progs/netcnt_prog.c | 29 +++++++-------
> tools/testing/selftests/bpf/test_netcnt.c | 25 +++++++-----
> 4 files changed, 72 insertions(+), 31 deletions(-)
>
> diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> index 7ed2a14dc0de..035e9e3a7132 100644
> --- a/kernel/bpf/local_storage.c
> +++ b/kernel/bpf/local_storage.c
> @@ -1,6 +1,7 @@
> //SPDX-License-Identifier: GPL-2.0
> #include <linux/bpf-cgroup.h>
> #include <linux/bpf.h>
> +#include <linux/bpf_local_storage.h>
> #include <linux/btf.h>
> #include <linux/bug.h>
> #include <linux/filter.h>
> @@ -283,9 +284,17 @@ static int cgroup_storage_get_next_key(struct bpf_map *_map, void *key,
>
> static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
> {
> + __u32 max_value_size = BPF_LOCAL_STORAGE_MAX_VALUE_SIZE;
> int numa_node = bpf_map_attr_numa_node(attr);
> struct bpf_cgroup_storage_map *map;
>
> + /* percpu is bound by PCPU_MIN_UNIT_SIZE, non-percu
> + * is the same as other local storages.
> + */
> + if (attr->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE)
> + max_value_size = min_t(__u32, max_value_size,
> + PCPU_MIN_UNIT_SIZE);
> +
> if (attr->key_size != sizeof(struct bpf_cgroup_storage_key) &&
> attr->key_size != sizeof(__u64))
> return ERR_PTR(-EINVAL);
> @@ -293,7 +302,7 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
> if (attr->value_size == 0)
> return ERR_PTR(-EINVAL);
>
> - if (attr->value_size > PAGE_SIZE)
> + if (attr->value_size > max_value_size)
> return ERR_PTR(-E2BIG);
>
> if (attr->map_flags & ~LOCAL_STORAGE_CREATE_FLAG_MASK ||
> diff --git a/tools/testing/selftests/bpf/netcnt_common.h b/tools/testing/selftests/bpf/netcnt_common.h
> index 81084c1c2c23..dfcf184ff713 100644
> --- a/tools/testing/selftests/bpf/netcnt_common.h
> +++ b/tools/testing/selftests/bpf/netcnt_common.h
> @@ -6,19 +6,43 @@
>
> #define MAX_PERCPU_PACKETS 32
>
> +/* sizeof(struct bpf_local_storage_elem):
> + *
> + * It really is about 128 bytes, but allocate more to account for possible

Maybe more specific to be 128 bytes on x86_64? As suggested below, 32bit
architecture may have smaller size.

Looks like that the size of struct bpf_local_storage_elem won't change
anytime soon, so it is probably okay to mention 128 bytes here.

> + * layout changes, different architectures, etc.
> + * It will wrap up to PAGE_SIZE internally anyway.

What will be wrap up to PAGE_SIZE? More explanations?

> + */
> +#define SIZEOF_BPF_LOCAL_STORAGE_ELEM 256
> +
> +/* Try to estimate kernel's BPF_LOCAL_STORAGE_MAX_VALUE_SIZE: */
> +#define BPF_LOCAL_STORAGE_MAX_VALUE_SIZE (0xFFFF - \
> + SIZEOF_BPF_LOCAL_STORAGE_ELEM)
> +
> +#define PCPU_MIN_UNIT_SIZE 32768
> +
> struct percpu_net_cnt {
> - __u64 packets;
> - __u64 bytes;
> + union {
> + struct {
> + __u64 packets;
> + __u64 bytes;
>
> - __u64 prev_ts;
> + __u64 prev_ts;
>
> - __u64 prev_packets;
> - __u64 prev_bytes;
> + __u64 prev_packets;
> + __u64 prev_bytes;
> + } val;

You don't need 'val' here. This way the code churn can be reduced.

> + __u8 data[PCPU_MIN_UNIT_SIZE];
> + };
> };
>
> struct net_cnt {
> - __u64 packets;
> - __u64 bytes;
> + union {
> + struct {
> + __u64 packets;
> + __u64 bytes;
> + } val;

The same here. 'val' is not needed.

> + __u8 data[BPF_LOCAL_STORAGE_MAX_VALUE_SIZE];
> + };
> };
>
> #endif
> diff --git a/tools/testing/selftests/bpf/progs/netcnt_prog.c b/tools/testing/selftests/bpf/progs/netcnt_prog.c
> index d071adf178bd..4b0884239892 100644
> --- a/tools/testing/selftests/bpf/progs/netcnt_prog.c
> +++ b/tools/testing/selftests/bpf/progs/netcnt_prog.c
> @@ -34,34 +34,35 @@ int bpf_nextcnt(struct __sk_buff *skb)
> cnt = bpf_get_local_storage(&netcnt, 0);
> percpu_cnt = bpf_get_local_storage(&percpu_netcnt, 0);
>
> - percpu_cnt->packets++;
> - percpu_cnt->bytes += skb->len;
> + percpu_cnt->val.packets++;
> + percpu_cnt->val.bytes += skb->len;
>
> - if (percpu_cnt->packets > MAX_PERCPU_PACKETS) {
> - __sync_fetch_and_add(&cnt->packets,
> - percpu_cnt->packets);
> - percpu_cnt->packets = 0;
> + if (percpu_cnt->val.packets > MAX_PERCPU_PACKETS) {
> + __sync_fetch_and_add(&cnt->val.packets,
> + percpu_cnt->val.packets);
> + percpu_cnt->val.packets = 0;
>
> - __sync_fetch_and_add(&cnt->bytes,
> - percpu_cnt->bytes);
> - percpu_cnt->bytes = 0;
> + __sync_fetch_and_add(&cnt->val.bytes,
> + percpu_cnt->val.bytes);
> + percpu_cnt->val.bytes = 0;
> }
>
> ts = bpf_ktime_get_ns();
> - dt = ts - percpu_cnt->prev_ts;
> + dt = ts - percpu_cnt->val.prev_ts;
>
> dt *= MAX_BPS;
> dt /= NS_PER_SEC;
>
> - if (cnt->bytes + percpu_cnt->bytes - percpu_cnt->prev_bytes < dt)
> + if (cnt->val.bytes + percpu_cnt->val.bytes -
> + percpu_cnt->val.prev_bytes < dt)
> ret = 1;
> else
> ret = 0;
>
> if (dt > REFRESH_TIME_NS) {
> - percpu_cnt->prev_ts = ts;
> - percpu_cnt->prev_packets = cnt->packets;
> - percpu_cnt->prev_bytes = cnt->bytes;
> + percpu_cnt->val.prev_ts = ts;
> + percpu_cnt->val.prev_packets = cnt->val.packets;
> + percpu_cnt->val.prev_bytes = cnt->val.bytes;
> }
>
> return !!ret;
> diff --git a/tools/testing/selftests/bpf/test_netcnt.c b/tools/testing/selftests/bpf/test_netcnt.c
> index a7b9a69f4fd5..1138765406a5 100644
> --- a/tools/testing/selftests/bpf/test_netcnt.c
> +++ b/tools/testing/selftests/bpf/test_netcnt.c
> @@ -33,11 +33,11 @@ static int bpf_find_map(const char *test, struct bpf_object *obj,
>
> int main(int argc, char **argv)
> {
> - struct percpu_net_cnt *percpu_netcnt;
> + struct percpu_net_cnt *percpu_netcnt = NULL;

Assigning NULL is not needed, right?

> struct bpf_cgroup_storage_key key;
> + struct net_cnt *netcnt = NULL;
> int map_fd, percpu_map_fd;
> int error = EXIT_FAILURE;
> - struct net_cnt netcnt;
> struct bpf_object *obj;
> int prog_fd, cgroup_fd;
> unsigned long packets;
> @@ -52,6 +52,12 @@ int main(int argc, char **argv)
> goto err;
> }
>
> + netcnt = malloc(sizeof(*netcnt));
> + if (!netcnt) {
> + printf("Not enough memory for non-per-cpu area\n");
> + goto err;
> + }
> +
> if (bpf_prog_load(BPF_PROG, BPF_PROG_TYPE_CGROUP_SKB,
> &obj, &prog_fd)) {
> printf("Failed to load bpf program\n");
> @@ -96,7 +102,7 @@ int main(int argc, char **argv)
> goto err;
> }
>
> - if (bpf_map_lookup_elem(map_fd, &key, &netcnt)) {
> + if (bpf_map_lookup_elem(map_fd, &key, netcnt)) {
> printf("Failed to lookup cgroup storage\n");
> goto err;
> }
> @@ -109,17 +115,17 @@ int main(int argc, char **argv)
> /* Some packets can be still in per-cpu cache, but not more than
> * MAX_PERCPU_PACKETS.
> */
> - packets = netcnt.packets;
> - bytes = netcnt.bytes;
> + packets = netcnt->val.packets;
> + bytes = netcnt->val.bytes;
> for (cpu = 0; cpu < nproc; cpu++) {
> - if (percpu_netcnt[cpu].packets > MAX_PERCPU_PACKETS) {
> + if (percpu_netcnt[cpu].val.packets > MAX_PERCPU_PACKETS) {
> printf("Unexpected percpu value: %llu\n",
> - percpu_netcnt[cpu].packets);
> + percpu_netcnt[cpu].val.packets);
> goto err;
> }
>
> - packets += percpu_netcnt[cpu].packets;
> - bytes += percpu_netcnt[cpu].bytes;
> + packets += percpu_netcnt[cpu].val.packets;
> + bytes += percpu_netcnt[cpu].val.bytes;
> }
>
> /* No packets should be lost */
> @@ -142,6 +148,7 @@ int main(int argc, char **argv)
> err:
> cleanup_cgroup_environment();
> free(percpu_netcnt);
> + free(netcnt);

Let us do
free(netcnt);
free(percpu_netcnt);
to follow the allocation order in a reverse way.

>
> out:
> return error;
>