Re: [Patch bpf-next] sock_map: include sk_psock memory overhead too

Yafang Shao
2023-04-02T10:41:52Z

On Sat, Apr 1, 2023 at 9:09 AM John Fastabend <john.fastabend@gmail.com> wrote:
>
> Yafang Shao wrote:
> > On Mon, Mar 27, 2023 at 6:16 AM Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > >
> > > From: Cong Wang <cong.wang@bytedance.com>
> > >
> > > When a socket is added to a sockmap, sk_psock is allocated too as its
> > > sk_user_data, therefore it should be consider as an overhead of sockmap
> > > memory usage.
> > >
> > > Before this patch:
> > >
> > > 1: sockmap flags 0x0
> > > key 4B value 4B max_entries 2 memlock 656B
> > > pids echo-sockmap(549)
> > >
> > > After this patch:
> > >
> > > 9: sockmap flags 0x0
> > > key 4B value 4B max_entries 2 memlock 1824B
> > > pids echo-sockmap(568)
> > >
> > > Fixes: 73d2c61919e9 ("bpf, net: sock_map memory usage")
> > > Cc: Yafang Shao <laoar.shao@gmail.com>
> > > Cc: Jakub Sitnicki <jakub@cloudflare.com>
> > > Cc: John Fastabend <john.fastabend@gmail.com>
> > > Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> > > ---
> > > net/core/sock_map.c | 10 +++++++++-
> > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> > > index 7c189c2e2fbf..22197e565ece 100644
> > > --- a/net/core/sock_map.c
> > > +++ b/net/core/sock_map.c
> > > @@ -799,9 +799,17 @@ static void sock_map_fini_seq_private(void *priv_data)
> > >
> > > static u64 sock_map_mem_usage(const struct bpf_map *map)
> > > {
> > > + struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
> > > u64 usage = sizeof(struct bpf_stab);
> > > + int i;
> > >
> > > usage += (u64)map->max_entries * sizeof(struct sock *);
> > > +
> > > + for (i = 0; i < stab->map.max_entries; i++) {
> >
> > Although it adds a for-loop, the operation below is quite light. So it
> > looks good to me.
>
> We could track a count from update to avoid the loop?
>

I prefer adding a count into struct bpf_stab. We can also get the
number of socks easily with this new count, and it should be
acceptable to modify this count in the update/delete paths.

--
Regards
Yafang