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

[Muchun Song]

On Mon, Oct 12, 2020 at 2:39 AM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>
> On Sat, Oct 10, 2020 at 3:39 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> 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