netdev - Re: [Patch bpf-next] sock_map: include sk

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Date:   Sun, 2 Apr 2023 18:41:08 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: Re: [Patch bpf-next] sock_map: include sk_psock memory overhead too

On Sat, Apr 1, 2023 at 9:09 AM John Fastabend <john.fastabend@...il.com> wrote:
>
> Yafang Shao wrote:
> > On Mon, Mar 27, 2023 at 6:16 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> > >
> > > From: Cong Wang <cong.wang@...edance.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@...il.com>
> > > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > > Cc: John Fastabend <john.fastabend@...il.com>
> > > Signed-off-by: Cong Wang <cong.wang@...edance.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