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

sdf
2021-07-26T15:39:13Z

On 07/25, Yonghong Song wrote:

> 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.
SG, I'll clarify that it's x86_64 only. Or do you want me to use 128
as SIZEOF_BPF_LOCAL_STORAGE_ELEM ?

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

> What will be wrap up to PAGE_SIZE? More explanations?

I'll reword to the following:

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.

(clarify that the kernel will wrap it up internally)

> > + */
> > +#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.
Good idea, dropping for both.

> > + __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?
Yeah, it's not needed, but I'd prefer to have it for consistency
(so both free() work regardless of the ordering and future changes).
Let me know if you strongly disagree, I can drop it.

> > 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.
Sure.

> > out:
> > return error;
> >