Messages in this thread | | | From | Cong Wang <> | Date | Mon, 12 Oct 2020 14:46:51 -0700 | Subject | Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo |
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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.
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