Re: [PATCH net-next] tcp: add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb()
From: Eric Dumazet
Date: Wed Sep 01 2021 - 11:16:22 EST
On Wed, Sep 1, 2021 at 8:06 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Wed, Sep 1, 2021 at 3:52 AM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> >
> > On Wed, 2021-09-01 at 18:39 +0800, Yunsheng Lin wrote:
> > > Since tcp_tx_skb_cache is disabled by default in:
> > > commit 0b7d7f6b2208 ("tcp: add tcp_tx_skb_cache sysctl")
> > >
> > > Add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb() to
> > > avoid possible branch-misses.
> > >
> > > Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
> >
> > Note that MPTCP is currently exploiting sk->sk_tx_skb_cache. If we get
> > this patch goes in as-is, it will break mptcp.
> >
> > One possible solution would be to let mptcp usage enable sk-
> > >sk_tx_skb_cache, but that has relevant side effects on plain TCP.
> >
> > Another options would be re-work once again the mptcp xmit path to
> > avoid using sk->sk_tx_skb_cache.
> >
>
> Hmmm, I actually wrote a revert of this feature but forgot to submit
> it last year.
>
> commit c36cfbd791f62c0f7c6b32132af59dfdbe6be21b (HEAD -> listener_scale4)
> Author: Eric Dumazet <edumazet@xxxxxxxxxx>
> Date: Wed May 20 06:38:38 2020 -0700
>
> tcp: remove sk_{tr}x_skb_cache
>
> This reverts the following patches :
>
> 2e05fcae83c41eb2df10558338dc600dc783af47 ("tcp: fix compile error
> if !CONFIG_SYSCTL")
> 4f661542a40217713f2cee0bb6678fbb30d9d367 ("tcp: fix zerocopy and
> notsent_lowat issues")
> 472c2e07eef045145bc1493cc94a01c87140780a ("tcp: add one skb cache for tx")
> 8b27dae5a2e89a61c46c6dbc76c040c0e6d0ed4c ("tcp: add one skb cache for rx")
>
> Having a cache of one skb (in each direction) per TCP socket is fragile,
> since it can cause a significant increase of memory needs,
> and not good enough for high speed flows anyway where more than one skb
> is needed.
>
> We want instead to add a generic infrastructure, with more flexible per-cpu
> caches, for alien NUMA nodes.
>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> I will update this commit to also remove the part in MPTCP.
>
> Let's remove this feature and replace it with something less costly.
Paolo, can you work on MPTP side, so that my revert can be then applied ?
Thanks !
From c36cfbd791f62c0f7c6b32132af59dfdbe6be21b Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Wed, 20 May 2020 06:38:38 -0700
Subject: [PATCH net-next] tcp: remove sk_{tr}x_skb_cache
This reverts the following patches :
2e05fcae83c41eb2df10558338dc600dc783af47 ("tcp: fix compile error if !CONFIG_SYSCTL")
4f661542a40217713f2cee0bb6678fbb30d9d367 ("tcp: fix zerocopy and notsent_lowat issues")
472c2e07eef045145bc1493cc94a01c87140780a ("tcp: add one skb cache for tx")
8b27dae5a2e89a61c46c6dbc76c040c0e6d0ed4c ("tcp: add one skb cache for rx")
Having a cache of one skb (in each direction) per TCP socket is fragile,
since it can cause a significant increase of memory needs,
and not good enough for high speed flows anyway where more than one skb
is needed.
We want instead to add a generic infrastructure, with more flexible per-cpu
caches, for alien NUMA nodes.
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
---
Documentation/networking/ip-sysctl.rst | 8 --------
include/net/sock.h | 19 -------------------
net/ipv4/af_inet.c | 4 ----
net/ipv4/sysctl_net_ipv4.c | 12 ------------
net/ipv4/tcp.c | 26 --------------------------
net/ipv4/tcp_ipv4.c | 6 ------
net/ipv6/tcp_ipv6.c | 6 ------
7 files changed, 81 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index d91ab28718d493bf5196f2b08cb59ec2c138e8e4..16b8bf72feaf42753121c368530a4f2e864a658f 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -989,14 +989,6 @@ tcp_challenge_ack_limit - INTEGER
in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
Default: 1000
-tcp_rx_skb_cache - BOOLEAN
- Controls a per TCP socket cache of one skb, that might help
- performance of some workloads. This might be dangerous
- on systems with a lot of TCP sockets, since it increases
- memory usage.
-
- Default: 0 (disabled)
-
UDP variables
=============
diff --git a/include/net/sock.h b/include/net/sock.h
index 66a9a90f9558e4c739e01192b3f8cee9fa271ae9..708b9de3cdbb116eb2d1e63ecbc8672d556f0951 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -262,7 +262,6 @@ struct bpf_local_storage;
* @sk_dst_cache: destination cache
* @sk_dst_pending_confirm: need to confirm neighbour
* @sk_policy: flow policy
- * @sk_rx_skb_cache: cache copy of recently accessed RX skb
* @sk_receive_queue: incoming packets
* @sk_wmem_alloc: transmit queue bytes committed
* @sk_tsq_flags: TCP Small Queues flags
@@ -328,7 +327,6 @@ struct bpf_local_storage;
* @sk_peek_off: current peek_offset value
* @sk_send_head: front of stuff to transmit
* @tcp_rtx_queue: TCP re-transmit queue [union with @sk_send_head]
- * @sk_tx_skb_cache: cache copy of recently accessed TX skb
* @sk_security: used by security modules
* @sk_mark: generic packet mark
* @sk_cgrp_data: cgroup data for this cgroup
@@ -393,7 +391,6 @@ struct sock {
atomic_t sk_drops;
int sk_rcvlowat;
struct sk_buff_head sk_error_queue;
- struct sk_buff *sk_rx_skb_cache;
struct sk_buff_head sk_receive_queue;
/*
* The backlog queue is special, it is always used with
@@ -442,7 +439,6 @@ struct sock {
struct sk_buff *sk_send_head;
struct rb_root tcp_rtx_queue;
};
- struct sk_buff *sk_tx_skb_cache;
struct sk_buff_head sk_write_queue;
__s32 sk_peek_off;
int sk_write_pending;
@@ -1555,18 +1551,10 @@ static inline void sk_mem_uncharge(struct sock *sk, int size)
__sk_mem_reclaim(sk, 1 << 20);
}
-DECLARE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key);
static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb)
{
sk_wmem_queued_add(sk, -skb->truesize);
sk_mem_uncharge(sk, skb->truesize);
- if (static_branch_unlikely(&tcp_tx_skb_cache_key) &&
- !sk->sk_tx_skb_cache && !skb_cloned(skb)) {
- skb_ext_reset(skb);
- skb_zcopy_clear(skb, true);
- sk->sk_tx_skb_cache = skb;
- return;
- }
__kfree_skb(skb);
}
@@ -2575,7 +2563,6 @@ static inline void skb_setup_tx_timestamp(struct sk_buff *skb, __u16 tsflags)
&skb_shinfo(skb)->tskey);
}
-DECLARE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key);
/**
* sk_eat_skb - Release a skb if it is no longer needed
* @sk: socket to eat this skb from
@@ -2587,12 +2574,6 @@ DECLARE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key);
static inline void sk_eat_skb(struct sock *sk, struct sk_buff *skb)
{
__skb_unlink(skb, &sk->sk_receive_queue);
- if (static_branch_unlikely(&tcp_rx_skb_cache_key) &&
- !sk->sk_rx_skb_cache) {
- sk->sk_rx_skb_cache = skb;
- skb_orphan(skb);
- return;
- }
__kfree_skb(skb);
}
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 1d816a5fd3eb914e0e3a071a7ae159d7311073f8..40558033f857c0ca7d98b778f70487e194f3d066 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -133,10 +133,6 @@ void inet_sock_destruct(struct sock *sk)
struct inet_sock *inet = inet_sk(sk);
__skb_queue_purge(&sk->sk_receive_queue);
- if (sk->sk_rx_skb_cache) {
- __kfree_skb(sk->sk_rx_skb_cache);
- sk->sk_rx_skb_cache = NULL;
- }
__skb_queue_purge(&sk->sk_error_queue);
sk_mem_reclaim(sk);
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 6f1e64d492328777bf8f167b56c01bc96b182e98..6eb43dc91218cea14134b66dfd2232ff2659babb 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -594,18 +594,6 @@ static struct ctl_table ipv4_table[] = {
.extra1 = &sysctl_fib_sync_mem_min,
.extra2 = &sysctl_fib_sync_mem_max,
},
- {
- .procname = "tcp_rx_skb_cache",
- .data = &tcp_rx_skb_cache_key.key,
- .mode = 0644,
- .proc_handler = proc_do_static_key,
- },
- {
- .procname = "tcp_tx_skb_cache",
- .data = &tcp_tx_skb_cache_key.key,
- .mode = 0644,
- .proc_handler = proc_do_static_key,
- },
{ }
};
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e8b48df73c852a48e51754ea98b1e08bf024bb9e..4a37500f4bd4422bda2609de520b83056c2cb01a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -325,11 +325,6 @@ struct tcp_splice_state {
unsigned long tcp_memory_pressure __read_mostly;
EXPORT_SYMBOL_GPL(tcp_memory_pressure);
-DEFINE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key);
-EXPORT_SYMBOL(tcp_rx_skb_cache_key);
-
-DEFINE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key);
-
void tcp_enter_memory_pressure(struct sock *sk)
{
unsigned long val;
@@ -866,18 +861,6 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
{
struct sk_buff *skb;
- if (likely(!size)) {
- skb = sk->sk_tx_skb_cache;
- if (skb) {
- skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
- sk->sk_tx_skb_cache = NULL;
- pskb_trim(skb, 0);
- INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
- skb_shinfo(skb)->tx_flags = 0;
- memset(TCP_SKB_CB(skb), 0, sizeof(struct tcp_skb_cb));
- return skb;
- }
- }
/* The TCP header must be at least 32-bit aligned. */
size = ALIGN(size, 4);
@@ -2920,11 +2903,6 @@ void tcp_write_queue_purge(struct sock *sk)
sk_wmem_free_skb(sk, skb);
}
tcp_rtx_queue_purge(sk);
- skb = sk->sk_tx_skb_cache;
- if (skb) {
- __kfree_skb(skb);
- sk->sk_tx_skb_cache = NULL;
- }
INIT_LIST_HEAD(&tcp_sk(sk)->tsorted_sent_queue);
sk_mem_reclaim(sk);
tcp_clear_all_retrans_hints(tcp_sk(sk));
@@ -2961,10 +2939,6 @@ int tcp_disconnect(struct sock *sk, int flags)
tcp_clear_xmit_timers(sk);
__skb_queue_purge(&sk->sk_receive_queue);
- if (sk->sk_rx_skb_cache) {
- __kfree_skb(sk->sk_rx_skb_cache);
- sk->sk_rx_skb_cache = NULL;
- }
WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
tp->urg_data = 0;
tcp_write_queue_purge(sk);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2e62e0d6373a6ee5d98756fb1967bff9743ffa02..29a57bd159f0aa99e892bac56b75961c107f803a 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1941,7 +1941,6 @@ static void tcp_v4_fill_cb(struct sk_buff *skb, const struct iphdr *iph,
int tcp_v4_rcv(struct sk_buff *skb)
{
struct net *net = dev_net(skb->dev);
- struct sk_buff *skb_to_free;
int sdif = inet_sdif(skb);
int dif = inet_iif(skb);
const struct iphdr *iph;
@@ -2082,17 +2081,12 @@ int tcp_v4_rcv(struct sk_buff *skb)
tcp_segs_in(tcp_sk(sk), skb);
ret = 0;
if (!sock_owned_by_user(sk)) {
- skb_to_free = sk->sk_rx_skb_cache;
- sk->sk_rx_skb_cache = NULL;
ret = tcp_v4_do_rcv(sk, skb);
} else {
if (tcp_add_backlog(sk, skb))
goto discard_and_relse;
- skb_to_free = NULL;
}
bh_unlock_sock(sk);
- if (skb_to_free)
- __kfree_skb(skb_to_free);
put_and_return:
if (refcounted)
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 0ce52d46e4f81b221a6acd4a0dd7b0d462dbac7a..8cf5ff2e95043ec1a2b27661aae884eb13dcf9eb 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1618,7 +1618,6 @@ static void tcp_v6_fill_cb(struct sk_buff *skb, const struct ipv6hdr *hdr,
INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
{
- struct sk_buff *skb_to_free;
int sdif = inet6_sdif(skb);
int dif = inet6_iif(skb);
const struct tcphdr *th;
@@ -1754,17 +1753,12 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
tcp_segs_in(tcp_sk(sk), skb);
ret = 0;
if (!sock_owned_by_user(sk)) {
- skb_to_free = sk->sk_rx_skb_cache;
- sk->sk_rx_skb_cache = NULL;
ret = tcp_v6_do_rcv(sk, skb);
} else {
if (tcp_add_backlog(sk, skb))
goto discard_and_relse;
- skb_to_free = NULL;
}
bh_unlock_sock(sk);
- if (skb_to_free)
- __kfree_skb(skb_to_free);
put_and_return:
if (refcounted)
sock_put(sk);
--
2.33.0.153.gba50c8fa24-goog