From: Eric Dumazet <eric.dumazet@gmail.com>
To: Muchun Song <songmuchun@bytedance.com>,
Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Greg KH <gregkh@linuxfoundation.org>,
rafael@kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
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Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
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Linux Kernel Network Developers <netdev@vger.kernel.org>,
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Subject: Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo
Date: Mon, 12 Oct 2020 11:24:05 +0200 [thread overview]
Message-ID: <9262ea44-fc3a-0b30-54dd-526e16df85d1@gmail.com> (raw)
In-Reply-To: <CAMZfGtXVKER_GM-wwqxrUshDzcEg9FkS3x_BaMTVyeqdYPGSkw@mail.gmail.com>
On 10/12/20 10:39 AM, Muchun Song wrote:
> On Mon, Oct 12, 2020 at 3:42 PM Eric Dumazet <edumazet@google.com> wrote:
>>
>> On Mon, Oct 12, 2020 at 6:22 AM 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
>>> 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.
>
> The 'mem' item in the /proc/net/sockstat does not represent real
> memory usage. This is just the total amount of charged memory.
>
> For example, if a task sends a 10-byte message, it only charges one
> page to memcg. But the system may allocate 8 pages. Therefore, it
> does not truly reflect the memory allocated by the above memory
> allocation path. We can see the difference via the following message.
>
> cat /proc/net/sockstat
> sockets: used 698
> TCP: inuse 70 orphan 0 tw 617 alloc 134 mem 13
> UDP: inuse 90 mem 4
> UDPLITE: inuse 0
> RAW: inuse 1
> FRAG: inuse 0 memory 0
>
> cat /proc/meminfo | grep Sock
> Sock: 13664 kB
>
> The /proc/net/sockstat only shows us that there are 17*4 kB TCP
> memory allocations. But apply this patch, we can see that we truly
> allocate 13664 kB(May be greater than this value because of per-cpu
> stat cache). Of course the load of the example here is not high. In
> some high load cases, I believe the difference here will be even
> greater.
>
This is great, but you have not addressed my feedback.
TCP memory allocations are bounded by /proc/sys/net/ipv4/tcp_mem
Fact that the memory is forward allocated or not is a detail.
If you think we must pre-allocate memory, instead of forward allocations,
your patch does not address this. Adding one line per consumer in /proc/meminfo looks
wrong to me.
If you do not want 9.37 % of physical memory being possibly used by TCP,
just change /proc/sys/net/ipv4/tcp_mem accordingly ?
next prev parent reply other threads:[~2020-10-12 9:24 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 [this message]
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
2020-10-13 3:29 ` Muchun Song
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