From: Cong Wang <xiyou.wangcong@gmail.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
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Subject: Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo
Date: Mon, 12 Oct 2020 14:46:51 -0700 [thread overview]
Message-ID: <CAM_iQpXLX1xXN02idk-yU1T=AGb9JmGiLkfRGCJOxjCw-OWpfQ@mail.gmail.com> (raw)
In-Reply-To: <CAMZfGtUhVx_iYY3bJZRY5s1PG0N1mCsYGS9Oku8cTqPiMDze-g@mail.gmail.com>
On Sun, Oct 11, 2020 at 9:22 PM Muchun Song <songmuchun@bytedance.com> wrote:
>
> 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> 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
Interesting, we already have a few counters related to socket buffers,
are you saying these are not accounted in /proc/meminfo either?
If yes, why are page frags so special here? If not, they are more
important than page frags, so you probably want to deal with them
first.
> 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.
It looks like actually the socket page frag is already accounted,
for example, the tcp_sendmsg_locked():
copy = min_t(int, copy, pfrag->size - pfrag->offset);
if (!sk_wmem_schedule(sk, copy))
goto wait_for_memory;
>
> >
> > > 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().
How is skb_page_frag_refill() possibly paired with __skb_frag_unref()?
> 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.
skb_page_frag_refill() is called on frags not within an skb, for instance,
sk_page_frag_refill() uses it for a per-socket or per-process page frag.
But, __skb_frag_unref() is specifically used for skb frags, which are
supposed to be filled by skb_fill_page_desc() (page is allocated by driver).
They are different things you are mixing them up, which looks clearly
wrong or at least misleading.
Thanks.
next prev parent reply other threads:[~2020-10-12 21:47 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-10 10:38 [PATCH] mm: proc: add Sock to /proc/meminfo Muchun Song
2020-10-10 16:36 ` Randy Dunlap
2020-10-11 4:42 ` [External] " Muchun Song
2020-10-11 13:52 ` Mike Rapoport
2020-10-11 16:00 ` [External] " Muchun Song
2020-10-11 18:39 ` Cong Wang
2020-10-12 4:22 ` [External] " Muchun Song
2020-10-12 7:42 ` Eric Dumazet
2020-10-12 8:39 ` Muchun Song
2020-10-12 9:24 ` Eric Dumazet
2020-10-12 9:53 ` Muchun Song
2020-10-12 22:12 ` Cong Wang
2020-10-13 3:52 ` Muchun Song
2020-10-13 6:55 ` Eric Dumazet
2020-10-13 8:09 ` Mike Rapoport
2020-10-13 14:43 ` Randy Dunlap
2020-10-13 15:12 ` Mike Rapoport
2020-10-13 15:21 ` Randy Dunlap
2020-10-14 5:34 ` Mike Rapoport
2020-10-13 15:28 ` Muchun Song
2020-10-16 15:38 ` Vlastimil Babka
2020-10-16 20:53 ` Minchan Kim
2020-10-19 17:23 ` Shakeel Butt
2020-10-12 21:46 ` Cong Wang [this message]
2020-10-13 3:29 ` Muchun Song
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