linux-kernel - Re: [PATCH] tcp: Add memory pressure flag to sockstat

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Message-ID: <30997.1689374702@famine>
Date:   Fri, 14 Jul 2023 15:45:02 -0700
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     Jamie Bainbridge <jamie.bainbridge@...il.com>
cc:     "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: Add memory pressure flag to sockstat

Jamie Bainbridge <jamie.bainbridge@...il.com> wrote:

>When tuning a system it can be helpful to know whether the protocol is
>in memory pressure state or not. This can be determined by corresponding
>the number of pages in "net.ipv4.tcp_mem" with the current allocation,
>but a global variable already tracks this as the source of truth.
>
>Expose that variable in sockstat where other protocol memory usage is
>already reported.
>
>Add "pressure" which is 0 in normal state and 1 under pressure:
>
> # grep TCP /proc/net/sockstat
> TCP: inuse 5 orphan 0 tw 0 alloc 7 mem 1 pressure 0
>
> # grep TCP /proc/net/sockstat
> TCP: inuse 5 orphan 0 tw 0 alloc 7 mem 1 pressure 1

	Isn't this already available in /proc/net/protocols?

protocol  size sockets  memory press maxhdr  slab module     cl co di ac io in de sh ss gs se re sp bi br ha uh gp em
[...]
UDP       1472      7       6   NI       0   yes  kernel      y  y  y  n  y  y  y  n  y  y  y  y  y  n  n  y  y  y  n
TCP       2512      5       1   no     320   yes  kernel      y  y  y  y  y  y  y  y  y  y  y  y  y  n  y  y  y  y  y

	-J

>Tested by writing a large value to global variable tcp_memory_pressure
>(it usually stores jiffies when memory pressure was entered) and not
>just by code review or editing example output.
>
>Signed-off-by: Jamie Bainbridge <jamie.bainbridge@...il.com>
>---
> net/ipv4/proc.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
>diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
>index eaf1d3113b62f7dc93fdc7b7c4041140ac63bf69..f4c5ced2de49d5c6d7f5d7ccdaa76c89dcf8c932 100644
>--- a/net/ipv4/proc.c
>+++ b/net/ipv4/proc.c
>@@ -51,16 +51,17 @@
> static int sockstat_seq_show(struct seq_file *seq, void *v)
> {
> 	struct net *net = seq->private;
>-	int orphans, sockets;
>+	int orphans, sockets, tcp_pressure;
> 
> 	orphans = tcp_orphan_count_sum();
> 	sockets = proto_sockets_allocated_sum_positive(&tcp_prot);
>+	tcp_pressure = READ_ONCE(tcp_memory_pressure) ? 1 : 0;
> 
> 	socket_seq_show(seq);
>-	seq_printf(seq, "TCP: inuse %d orphan %d tw %d alloc %d mem %ld\n",
>+	seq_printf(seq, "TCP: inuse %d orphan %d tw %d alloc %d mem %ld pressure %d\n",
> 		   sock_prot_inuse_get(net, &tcp_prot), orphans,
> 		   refcount_read(&net->ipv4.tcp_death_row.tw_refcount) - 1,
>-		   sockets, proto_memory_allocated(&tcp_prot));
>+		   sockets, proto_memory_allocated(&tcp_prot), tcp_pressure);
> 	seq_printf(seq, "UDP: inuse %d mem %ld\n",
> 		   sock_prot_inuse_get(net, &udp_prot),
> 		   proto_memory_allocated(&udp_prot));
>-- 
>2.41.0
>
>

---
	-Jay Vosburgh, jay.vosburgh@...onical.com