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Date: Tue, 27 Jul 2021 12:32:33 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Stanislav Fomichev <sdf@...gle.com>
Cc: Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next v3] bpf: increase supported cgroup storage value size
On Mon, Jul 26, 2021 at 4:00 PM Stanislav Fomichev <sdf@...gle.com> 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).
>
> v3:
> * refine SIZEOF_BPF_LOCAL_STORAGE_ELEM comment (Yonghong Song)
> * anonymous struct in percpu_net_cnt & net_cnt (Yonghong Song)
> * reorder free (Yonghong Song)
>
> v2:
> * cap max_value_size instead of BUILD_BUG_ON (Martin KaFai Lau)
>
> Cc: Martin KaFai Lau <kafai@...com>
> Cc: Yonghong Song <yhs@...com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> kernel/bpf/local_storage.c | 11 +++++-
> tools/testing/selftests/bpf/netcnt_common.h | 38 +++++++++++++++++----
> tools/testing/selftests/bpf/test_netcnt.c | 17 ++++++---
> 3 files changed, 53 insertions(+), 13 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..87f5b97e1932 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 on x86_64, but allocate more to account for
> + * possible layout changes, different architectures, etc.
> + * The kernel will wrap up to PAGE_SIZE internally anyway.
> + */
> +#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 {
so you have a struct with a single anonymous union inside, isn't that
right? Any problems with just making struct percpu_net_cnt into union
percpu_net_cnt?
> + struct {
> + __u64 packets;
> + __u64 bytes;
>
> - __u64 prev_ts;
> + __u64 prev_ts;
>
> - __u64 prev_packets;
> - __u64 prev_bytes;
> + __u64 prev_packets;
> + __u64 prev_bytes;
> + };
> + __u8 data[PCPU_MIN_UNIT_SIZE];
> + };
> };
>
> struct net_cnt {
> - __u64 packets;
> - __u64 bytes;
> + union {
similarly here
> + struct {
> + __u64 packets;
> + __u64 bytes;
> + };
> + __u8 data[BPF_LOCAL_STORAGE_MAX_VALUE_SIZE];
> + };
> };
>
> #endif
> diff --git a/tools/testing/selftests/bpf/test_netcnt.c b/tools/testing/selftests/bpf/test_netcnt.c
> index a7b9a69f4fd5..372afccf2d17 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;
> 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));
curious, was it too big to be just allocated on the stack? Isn't the
thread stack size much bigger than 64KB (at least by default)?
> + 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;
> }
> @@ -109,8 +115,8 @@ 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->packets;
> + bytes = netcnt->bytes;
> for (cpu = 0; cpu < nproc; cpu++) {
> if (percpu_netcnt[cpu].packets > MAX_PERCPU_PACKETS) {
> printf("Unexpected percpu value: %llu\n",
> @@ -141,6 +147,7 @@ int main(int argc, char **argv)
>
> err:
> cleanup_cgroup_environment();
> + free(netcnt);
> free(percpu_netcnt);
>
> out:
> --
> 2.32.0.432.gabb21c7263-goog
>
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