netdev - Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo

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Date:   Mon, 12 Oct 2020 09:42:37 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Shakeel Butt <shakeelb@...gle.com>,
        Will Deacon <will@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Roman Gushchin <guro@...com>, Neil Brown <neilb@...e.de>,
        rppt@...nel.org, Sami Tolvanen <samitolvanen@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Feng Tang <feng.tang@...el.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Florian Westphal <fw@...len.de>, gustavoars@...nel.org,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>, dave@...olabs.net,
        Michel Lespinasse <walken@...gle.com>,
        Jann Horn <jannh@...gle.com>, chenqiwu@...omi.com,
        christophe.leroy@....fr, Minchan Kim <minchan@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo

On Mon, Oct 12, 2020 at 6:22 AM Muchun Song <songmuchun@...edance.com> wrote:
>
> On Mon, Oct 12, 2020 at 2:39 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > On Sat, Oct 10, 2020 at 3:39 AM Muchun Song <songmuchun@...edance.com> wrote:
> > >
> > > 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 kernel
> >
> > 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 user
> can't think of the socket buffer, naturally they will not `ss -m`. The
> end result
> is that we still don’t know where the memory is consumed. And we add the
> Sock to the /proc/meminfo just like the memcg does('sock' item in the cgroup
> 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 = 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.
>

Pages can be transferred from pipe to socket, socket to pipe (splice()
and zerocopy friends...)

 If you want to track TCP memory allocations, you always can look at
/proc/net/sockstat,
without adding yet another expensive memory accounting.