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

[sdf@google.com]

On 07/23, Martin KaFai Lau wrote:
> On Thu, Jul 22, 2021 at 05:27:47PM -0700, 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).
> >
> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > ---
> >  kernel/bpf/local_storage.c                    | 12 +++++-
> >  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, 73 insertions(+), 31 deletions(-)
> >
> > diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> > index 7ed2a14dc0de..a276da74c20a 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>
> > @@ -284,8 +285,17 @@ 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)
> >  {
> >  	int numa_node = bpf_map_attr_numa_node(attr);
> > +	__u32 max_value_size = PCPU_MIN_UNIT_SIZE;
> >  	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_CGROUP_STORAGE)
> > +		max_value_size = BPF_LOCAL_STORAGE_MAX_VALUE_SIZE;
> > +
> > +	BUILD_BUG_ON(PCPU_MIN_UNIT_SIZE > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE);
> If PCPU_MIN_UNIT_SIZE did become larger, I assume it would be bounded by
> BPF_LOCAL_STORAGE_MAX_VALUE_SIZE again?

> Instead of BUILD_BUG_ON, how about a min_t here:

> 	if (attr->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE)
> 		max_value_size = min_t(__u32,
> 					BPF_LOCAL_STORAGE_MAX_VALUE_SIZE,
> 					PCPU_MIN_UNIT_SIZE);

Sounds like a much better idea, thanks, will incorporate into v2.