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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Mon, 12 Oct 2020 12:22:16 +0800
Message-ID: <CAMZfGtUhVx_iYY3bJZRY5s1PG0N1mCsYGS9Oku8cTqPiMDze-g@mail.gmail.com>
Subject: Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo
To:     Cong Wang <xiyou.wangcong@gmail.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>, rafael@kernel.org,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Eric Dumazet <edumazet@google.com>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Shakeel Butt <shakeelb@google.com>,
        Will Deacon <will@kernel.org>, Michal Hocko <mhocko@suse.com>,
        Roman Gushchin <guro@fb.com>, Neil Brown <neilb@suse.de>,
        rppt@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Feng Tang <feng.tang@intel.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Willem de Bruijn <willemb@google.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Florian Westphal <fw@strlen.de>, gustavoars@kernel.org,
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        Linux Kernel Network Developers <netdev@vger.kernel.org>,
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On Mon, Oct 12, 2020 at 2:39 AM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> On Sat, Oct 10, 2020 at 3:39 AM Muchun Song <songmuchun@bytedance.com> wr=
ote:
> >
> > The amount of memory allocated to sockets buffer can become significant=
.
> > However, we do not display the amount of memory consumed by sockets
> > buffer. In this case, knowing where the memory is consumed by the kerne=
l
>
> We do it via `ss -m`. Is it not sufficient? And if not, why not adding it=
 there
> rather than /proc/meminfo?

If the system has little free memory, we can know where the memory is via
/proc/meminfo. If a lot of memory is consumed by socket buffer, we cannot
know it when the Sock is not shown in the /proc/meminfo. If the unaware use=
r
can't think of the socket buffer, naturally they will not `ss -m`. The
end result
is that we still don=E2=80=99t know where the memory is consumed. And we ad=
d the
Sock to the /proc/meminfo just like the memcg does('sock' item in the cgrou=
p
v2 memory.stat). So I think that adding to /proc/meminfo is sufficient.

>
> >  static inline void __skb_frag_unref(skb_frag_t *frag)
> >  {
> > -       put_page(skb_frag_page(frag));
> > +       struct page *page =3D skb_frag_page(frag);
> > +
> > +       if (put_page_testzero(page)) {
> > +               dec_sock_node_page_state(page);
> > +               __put_page(page);
> > +       }
> >  }
>
> You mix socket page frag with skb frag at least, not sure this is exactly
> what you want, because clearly skb page frags are frequently used
> by network drivers rather than sockets.
>
> Also, which one matches this dec_sock_node_page_state()? Clearly
> not skb_fill_page_desc() or __skb_frag_ref().

Yeah, we call inc_sock_node_page_state() in the skb_page_frag_refill().
So if someone gets the page returned by skb_page_frag_refill(), it must
put the page via __skb_frag_unref()/skb_frag_unref(). We use PG_private
to indicate that we need to dec the node page state when the refcount of
page reaches zero.

Thanks.

>
> Thanks.


--=20
Yours,
Muchun