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

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

[Randy Dunlap]

Hi,

On 10/10/20 3:38 AM, Muchun Song 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
> is very difficult. On our server with 500GB RAM, sometimes we can see
> 25GB disappear through /proc/meminfo. After our analysis, we found the
> following memory allocation path which consumes the memory with page_owner
> enabled.
> 
>   849698 times:
>   Page allocated via order 3, mask 0x4052c0(GFP_NOWAIT|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP)
>    __alloc_pages_nodemask+0x11d/0x290
>    skb_page_frag_refill+0x68/0xf0
>    sk_page_frag_refill+0x19/0x70
>    tcp_sendmsg_locked+0x2f4/0xd10
>    tcp_sendmsg+0x29/0xa0
>    sock_sendmsg+0x30/0x40
>    sock_write_iter+0x8f/0x100
>    __vfs_write+0x10b/0x190
>    vfs_write+0xb0/0x190
>    ksys_write+0x5a/0xd0
>    do_syscall_64+0x5d/0x110
>    entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  drivers/base/node.c      |  2 ++
>  drivers/net/virtio_net.c |  3 +--
>  fs/proc/meminfo.c        |  1 +
>  include/linux/mmzone.h   |  1 +
>  include/linux/skbuff.h   | 43 ++++++++++++++++++++++++++++++++++++++--
>  kernel/exit.c            |  3 +--
>  mm/page_alloc.c          |  7 +++++--
>  mm/vmstat.c              |  1 +
>  net/core/sock.c          |  8 ++++----
>  net/ipv4/tcp.c           |  3 +--
>  net/xfrm/xfrm_state.c    |  3 +--
>  11 files changed, 59 insertions(+), 16 deletions(-)

Thanks for finding that.

Please update Documentation/filesystems/proc.rst "meminfo" section also.

-- 
~Randy

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

[Cong Wang]

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?

>  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().

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

[Eric Dumazet]

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 ?


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

[Cong Wang]

On Mon, Oct 12, 2020 at 2:53 AM Muchun Song <songmuchun@bytedance.com> wrote:
> We are not complaining about TCP using too much memory, but how do
> we know that TCP uses a lot of memory. When I firstly face this problem,
> I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
> If we can know the amount memory of the socket buffer via /proc/meminfo, we
> may not need to spend a lot of time troubleshooting this problem. Not everyone
> knows that a lot of memory may be used here. But I believe many people
> should know /proc/meminfo to confirm memory users.

Well, I'd bet networking people know `ss -m` better than /proc/meminfo,
generally speaking.

The practice here is that if you want some networking-specific counters,
add it to where networking people know better, that is, `ss -m` or /proc/net/...

Or maybe the problem you described is not specific to networking at all,
there must be some other places where pages are allocated but not charged.
If so, adding a general mm counter in /proc/meminfo makes sense, but
it won't be specific to networking.

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

[Eric Dumazet]

On 10/12/20 11:53 AM, Muchun Song wrote:

> We are not complaining about TCP using too much memory, but how do
> we know that TCP uses a lot of memory. When I firstly face this problem,
> I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
> If we can know the amount memory of the socket buffer via /proc/meminfo, we
> may not need to spend a lot of time troubleshooting this problem. Not everyone
> knows that a lot of memory may be used here. But I believe many people
> should know /proc/meminfo to confirm memory users.

Adding yet another operations in networking fast path is a high cost to pay
just to add one extra line in /proc/meminfo, while /proc/net/sockstat
is already a good proxy, with per protocol details, instead of a single bucket.

I reiterate that zero copy would make this counter out of sync,
unless special support is added (adding yet another operations ?)

Also your patch does not address gazillions of page allocations from drivers
in RX path.

Here at Google the majority of networking mm usage when hosts are under stress
is in RX path, when out of order queues start to grow in TCP sockets.

Allocations in TX path were greatly reduced and optimally sized with the introduction
of /proc/sys/net/ipv4/tcp_notsent_lowat.

We have gazillions of put_page()/__free_page()/__free_pages()/alloc_page()/... all
over the places, adding yet another tracking of "this page is used by networking stacks"
is going to be quite a big project.

I thought memcg was a better goal in the long run, lets focus on it.



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

[Randy Dunlap]

On 10/13/20 1:09 AM, Mike Rapoport wrote:
> On Mon, Oct 12, 2020 at 05:53:01PM +0800, Muchun Song wrote:
>> On Mon, Oct 12, 2020 at 5:24 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>>>
>>> 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.
>>
>> I think that the consumer which consumes a lot of memory should be added
>> to the /proc/meminfo. This can help us know the user of large memory.
>>
>>>
>>> If you do not want 9.37 % of physical memory being possibly used by TCP,
>>> just change /proc/sys/net/ipv4/tcp_mem accordingly ?
>>
>> We are not complaining about TCP using too much memory, but how do
>> we know that TCP uses a lot of memory. When I firstly face this problem,
>> I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
>> If we can know the amount memory of the socket buffer via /proc/meminfo, we
>> may not need to spend a lot of time troubleshooting this problem. Not everyone
>> knows that a lot of memory may be used here. But I believe many people
>> should know /proc/meminfo to confirm memory users.
> 
> If I undestand correctly, the problem you are trying to solve is to
> simplify troubleshooting of memory usage for people who may not be aware
> that networking stack can be a large memory consumer.
> 
> For that a paragraph in 'man 5 proc' maybe a good start:
> 
>>From ddbcf38576d1a2b0e36fe25a27350d566759b664 Mon Sep 17 00:00:00 2001
> From: Mike Rapoport <rppt@linux.ibm.com>
> Date: Tue, 13 Oct 2020 11:07:35 +0300
> Subject: [PATCH] proc.5: meminfo: add not anout network stack memory
>  consumption
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>  man5/proc.5 | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/man5/proc.5 b/man5/proc.5
> index ed309380b..8414676f1 100644
> --- a/man5/proc.5
> +++ b/man5/proc.5
> @@ -3478,6 +3478,14 @@ Except as noted below,
>  all of the fields have been present since at least Linux 2.6.0.
>  Some fields are displayed only if the kernel was configured
>  with various options; those dependencies are noted in the list.
> +.IP
> +Note that significant part of memory allocated by the network stack
> +is not accounted in the file.
> +The memory consumption of the network stack can be queried
> +using
> +.IR /proc/net/sockstat
> +or
> +.BR ss (8)
>  .RS
>  .TP
>  .IR MemTotal " %lu"

Hi Mike,

Could you tell us what units those values are in?
or is that already explained somewhere else?

thanks.
-- 
~Randy

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

[Randy Dunlap]

On 10/13/20 8:12 AM, Mike Rapoport wrote:
> On Tue, Oct 13, 2020 at 07:43:59AM -0700, Randy Dunlap wrote:
>> On 10/13/20 1:09 AM, Mike Rapoport wrote:
>>> On Mon, Oct 12, 2020 at 05:53:01PM +0800, Muchun Song wrote:
>>>> On Mon, Oct 12, 2020 at 5:24 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
>>>>>
>>>>> 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:
>>>>
>>>> We are not complaining about TCP using too much memory, but how do
>>>> we know that TCP uses a lot of memory. When I firstly face this problem,
>>>> I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
>>>> If we can know the amount memory of the socket buffer via /proc/meminfo, we
>>>> may not need to spend a lot of time troubleshooting this problem. Not everyone
>>>> knows that a lot of memory may be used here. But I believe many people
>>>> should know /proc/meminfo to confirm memory users.
>>>
>>> If I undestand correctly, the problem you are trying to solve is to
>>> simplify troubleshooting of memory usage for people who may not be aware
>>> that networking stack can be a large memory consumer.
>>>
>>> For that a paragraph in 'man 5 proc' maybe a good start:
>>>
>>> >From ddbcf38576d1a2b0e36fe25a27350d566759b664 Mon Sep 17 00:00:00 2001
>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>> Date: Tue, 13 Oct 2020 11:07:35 +0300
>>> Subject: [PATCH] proc.5: meminfo: add not anout network stack memory
>>>  consumption
>>>
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>> ---
>>>  man5/proc.5 | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/man5/proc.5 b/man5/proc.5
>>> index ed309380b..8414676f1 100644
>>> --- a/man5/proc.5
>>> +++ b/man5/proc.5
>>> @@ -3478,6 +3478,14 @@ Except as noted below,
>>>  all of the fields have been present since at least Linux 2.6.0.
>>>  Some fields are displayed only if the kernel was configured
>>>  with various options; those dependencies are noted in the list.
>>> +.IP
>>> +Note that significant part of memory allocated by the network stack
>>> +is not accounted in the file.
>>> +The memory consumption of the network stack can be queried
>>> +using
>>> +.IR /proc/net/sockstat
>>> +or
>>> +.BR ss (8)
>>>  .RS
>>>  .TP
>>>  .IR MemTotal " %lu"
>>
>> Hi Mike,
>>
>> Could you tell us what units those values are in?
>> or is that already explained somewhere else?
> 
> It is described a few lines above and anyway, "MemTotal" is a part of
> the diff context ;-)

with no units AFAICT.

But I was unclear. I wasn't referring to /proc/meminfo, but instead
to /proc/net/sockstat and its units:

sockets: used 1224
TCP: inuse 11 orphan 1 tw 1 alloc 26 mem 3
UDP: inuse 4 mem 2
UDPLITE: inuse 0
RAW: inuse 0
FRAG: inuse 0 memory 0

E.g., for TCP and UDP, are those socket counts or some unit of memory?
If units of memory, what unit size?

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

[Vlastimil Babka]

On 10/13/20 10:09 AM, Mike Rapoport wrote:
>> We are not complaining about TCP using too much memory, but how do
>> we know that TCP uses a lot of memory. When I firstly face this problem,
>> I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
>> If we can know the amount memory of the socket buffer via /proc/meminfo, we
>> may not need to spend a lot of time troubleshooting this problem. Not everyone
>> knows that a lot of memory may be used here. But I believe many people
>> should know /proc/meminfo to confirm memory users.
> If I undestand correctly, the problem you are trying to solve is to
> simplify troubleshooting of memory usage for people who may not be aware
> that networking stack can be a large memory consumer.
> 
> For that a paragraph in 'man 5 proc' maybe a good start:

Yeah. Another major consumer that I've seen at some point was xfs buffers. And 
there might be others, and adding everything to /proc/meminfo is not feasible. I 
have once proposed adding a counter called "Unaccounted:" which would at least 
tell the user easily if a significant portion is occupied by memory not 
explained by the other meminfo counters, and look for trends (increase = 
potential memory leak?). For specific prominent consumers not covered by meminfo 
but that have some kind of internal counters, we could document where to look, 
such as /proc/net/sockstat or maybe create some /proc/ or /sys directory with 
file per consumer so that it's still easy to check, but without the overhead of 
global counters and bloated /proc/meminfo?

>  From ddbcf38576d1a2b0e36fe25a27350d566759b664 Mon Sep 17 00:00:00 2001
> From: Mike Rapoport<rppt@linux.ibm.com>
> Date: Tue, 13 Oct 2020 11:07:35 +0300
> Subject: [PATCH] proc.5: meminfo: add not anout network stack memory
>   consumption
> 
> Signed-off-by: Mike Rapoport<rppt@linux.ibm.com>
> ---
>   man5/proc.5 | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/man5/proc.5 b/man5/proc.5
> index ed309380b..8414676f1 100644
> --- a/man5/proc.5
> +++ b/man5/proc.5
> @@ -3478,6 +3478,14 @@ Except as noted below,
>   all of the fields have been present since at least Linux 2.6.0.
>   Some fields are displayed only if the kernel was configured
>   with various options; those dependencies are noted in the list.
> +.IP
> +Note that significant part of memory allocated by the network stack
> +is not accounted in the file.
> +The memory consumption of the network stack can be queried
> +using
> +.IR /proc/net/sockstat
> +or
> +.BR ss (8)
>   .RS
>   .TP
>   .IR MemTotal " %lu"
> -- 2.25.4

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

[Minchan Kim]

On Fri, Oct 16, 2020 at 05:38:26PM +0200, Vlastimil Babka wrote:
> On 10/13/20 10:09 AM, Mike Rapoport wrote:
> > > We are not complaining about TCP using too much memory, but how do
> > > we know that TCP uses a lot of memory. When I firstly face this problem,
> > > I do not know who uses the 25GB memory and it is not shown in the /proc/meminfo.
> > > If we can know the amount memory of the socket buffer via /proc/meminfo, we
> > > may not need to spend a lot of time troubleshooting this problem. Not everyone
> > > knows that a lot of memory may be used here. But I believe many people
> > > should know /proc/meminfo to confirm memory users.
> > If I undestand correctly, the problem you are trying to solve is to
> > simplify troubleshooting of memory usage for people who may not be aware
> > that networking stack can be a large memory consumer.
> > 
> > For that a paragraph in 'man 5 proc' maybe a good start:
> 
> Yeah. Another major consumer that I've seen at some point was xfs buffers.

As well, there are other various type of memory consumers in embedded world,
depending on the features what they supprted, too. They often tempted to add
the memory consumption into /proc/meminfo or /proc/vmstat, too to get
memory visibility.

> And there might be others, and adding everything to /proc/meminfo is not
> feasible. I have once proposed adding a counter called "Unaccounted:" which
> would at least tell the user easily if a significant portion is occupied by
> memory not explained by the other meminfo counters, and look for trends
> (increase = potential memory leak?). For specific prominent consumers not
> covered by meminfo but that have some kind of internal counters, we could
> document where to look, such as /proc/net/sockstat or maybe create some
> /proc/ or /sys directory with file per consumer so that it's still easy to
> check, but without the overhead of global counters and bloated
> /proc/meminfo?

What have in my mind is to support simple general sysfs infra from MM for
driver/subysstems rather than creating each own memory stat. The API
could support flexible accounting like just global memory consumption and/or
consmption by key(e.g,. pid or each own special) for the detail.

So, they are all shown under /sys/kernel/mm/misc/ with detail as well as
/proc/meminfo with simple line for global.

Furthermore, I'd like to plug the infra into OOM message so once OOM occurs,
we could print each own hidden memory usage from driver side if the driver
believe they could be memory hogger. It would make easier to detect
such kinds of leak or hogging as well as better maintainace.
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Re: [External] Re: [PATCH] mm: proc: add Sock to /proc/meminfo

[Cong Wang]

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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