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

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Message-ID: <CAMZfGtUhVx_iYY3bJZRY5s1PG0N1mCsYGS9Oku8cTqPiMDze-g@mail.gmail.com>
Date:   Mon, 12 Oct 2020 12:22:16 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     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>,
        Eric Dumazet <edumazet@...gle.com>,
        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>, 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 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.

Thanks.

>
> Thanks.



-- 
Yours,
Muchun