The more sockets we have in the hash table, the more time we spend
looking up the socket. While running a number of small workloads on
the same host, they penalise each other and cause performance degradation.
Also, the root cause might be a single workload that consumes much more
resources than the others. It often happens on a cloud service where
different workloads share the same computing resource.
To resolve the issue, we introduce an optional per-netns hash table for
TCP, but it's just ehash, and we still share the global bhash and lhash2.
With a smaller ehash, we can look up non-listener sockets faster and
isolate such noisy neighbours. Also, we can reduce lock contention.
We can control the ehash size by a new sysctl knob. However, depending
on workloads, it will require very sensitive tuning, so we disable the
feature by default (net.ipv4.tcp_child_ehash_entries == 0). Moreover,
we can fall back to using the global ehash in case we fail to allocate
enough memory for a new ehash.
We can check the current ehash size by another read-only sysctl knob,
net.ipv4.tcp_ehash_entries. A negative value means the netns shares
the global ehash (per-netns ehash is disabled or failed to allocate
memory).
# dmesg | cut -d ' ' -f 5- | grep "established hash"
TCP established hash table entries: 524288 (order: 10, 4194304 bytes, vmalloc hugepage)
# sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = 524288 # can be changed by thash_entries
# sysctl net.ipv4.tcp_child_ehash_entries
net.ipv4.tcp_child_ehash_entries = 0 # disabled by default
# ip netns add test1
# ip netns exec test1 sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = -524288 # share the global ehash
# sysctl -w net.ipv4.tcp_child_ehash_entries=100
net.ipv4.tcp_child_ehash_entries = 100
# sysctl net.ipv4.tcp_child_ehash_entries
net.ipv4.tcp_child_ehash_entries = 128 # rounded up to 2^n
# ip netns add test2
# ip netns exec test2 sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = 128 # own per-netns ehash
When more than two processes in the same netns create per-netns ehash
concurrently with different sizes, we need to guarantee the size in
one of the following ways:
1) Share the global ehash and create per-netns ehash
First, unshare() with tcp_child_ehash_entries==0. It creates dedicated
netns sysctl knobs where we can safely change tcp_child_ehash_entries
and clone()/unshare() to create a per-netns ehash.
2) Lock the sysctl knob
We can use flock(LOCK_MAND) or BPF_PROG_TYPE_CGROUP_SYSCTL to allow/deny
read/write on sysctl knobs.
Note the default values of two sysctl knobs depend on the ehash size and
should be tuned carefully:
tcp_max_tw_buckets : tcp_child_ehash_entries / 2
tcp_max_syn_backlog : max(128, tcp_child_ehash_entries / 128)
Also, we could optimise ehash lookup/iteration further by removing netns
comparison for the per-netns ehash in the future.
As a bonus, we can dismantle netns faster. Currently, while destroying
netns, we call inet_twsk_purge(), which walks through the global ehash.
It can be potentially big because it can have many sockets other than
TIME_WAIT in all netns. Splitting ehash changes that situation, where
it's only necessary for inet_twsk_purge() to clean up TIME_WAIT sockets
in each netns.
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---
Documentation/networking/ip-sysctl.rst | 20 +++++++++
include/net/inet_hashtables.h | 6 +++
include/net/netns/ipv4.h | 1 +
net/dccp/proto.c | 2 +
net/ipv4/inet_hashtables.c | 57 ++++++++++++++++++++++++++
net/ipv4/inet_timewait_sock.c | 4 +-
net/ipv4/sysctl_net_ipv4.c | 57 ++++++++++++++++++++++++++
net/ipv4/tcp.c | 1 +
net/ipv4/tcp_ipv4.c | 53 ++++++++++++++++++++----
net/ipv6/tcp_ipv6.c | 12 +++++-
10 files changed, 202 insertions(+), 11 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 56cd4ea059b2..97a0952b11e3 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1037,6 +1037,26 @@ tcp_challenge_ack_limit - INTEGER
in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
Default: 1000
+tcp_ehash_entries - INTEGER
+ Read-only number of hash buckets for TCP sockets in the current
+ networking namespace.
+
+ A negative value means the networking namespace does not own its
+ hash buckets and shares the initial networking namespace's one.
+
+tcp_child_ehash_entries - INTEGER
+ Control the number of hash buckets for TCP sockets in the child
+ networking namespace, which must be set before clone() or unshare().
+
+ The written value except for 0 is rounded up to 2^n. 0 is a special
+ value, meaning the child networking namespace will share the initial
+ networking namespace's hash buckets.
+
+ Note that the child will use the global one in case the kernel
+ fails to allocate enough memory.
+
+ Default: 0
+
UDP variables
=============
diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 2c866112433e..039440936ab2 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -168,6 +168,8 @@ struct inet_hashinfo {
/* The 2nd listener table hashed by local port and address */
unsigned int lhash2_mask;
struct inet_listen_hashbucket *lhash2;
+
+ bool pernet;
};
static inline struct inet_hashinfo *inet_get_hashinfo(const struct sock *sk)
@@ -214,6 +216,10 @@ static inline void inet_ehash_locks_free(struct inet_hashinfo *hashinfo)
hashinfo->ehash_locks = NULL;
}
+struct inet_hashinfo *inet_pernet_hashinfo_alloc(struct inet_hashinfo *hashinfo,
+ unsigned int ehash_entries);
+void inet_pernet_hashinfo_free(struct inet_hashinfo *hashinfo);
+
struct inet_bind_bucket *
inet_bind_bucket_create(struct kmem_cache *cachep, struct net *net,
struct inet_bind_hashbucket *head,
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index c7320ef356d9..6d9c01879027 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -170,6 +170,7 @@ struct netns_ipv4 {
int sysctl_tcp_pacing_ca_ratio;
int sysctl_tcp_wmem[3];
int sysctl_tcp_rmem[3];
+ unsigned int sysctl_tcp_child_ehash_entries;
unsigned long sysctl_tcp_comp_sack_delay_ns;
unsigned long sysctl_tcp_comp_sack_slack_ns;
int sysctl_max_syn_backlog;
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 7cd4a6cc99fc..c548ca3e9b0e 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1197,6 +1197,8 @@ static int __init dccp_init(void)
INIT_HLIST_HEAD(&dccp_hashinfo.bhash2[i].chain);
}
+ dccp_hashinfo.pernet = false;
+
rc = dccp_mib_init();
if (rc)
goto out_free_dccp_bhash2;
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 5eb21a95179b..a57932b14bc6 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -1145,3 +1145,60 @@ int inet_ehash_locks_alloc(struct inet_hashinfo *hashinfo)
return 0;
}
EXPORT_SYMBOL_GPL(inet_ehash_locks_alloc);
+
+struct inet_hashinfo *inet_pernet_hashinfo_alloc(struct inet_hashinfo *hashinfo,
+ unsigned int ehash_entries)
+{
+ struct inet_hashinfo *new_hashinfo;
+ int i;
+
+ new_hashinfo = kmalloc(sizeof(*new_hashinfo), GFP_KERNEL);
+ if (!new_hashinfo)
+ goto err;
+
+ new_hashinfo->ehash = kvmalloc_array(ehash_entries,
+ sizeof(struct inet_ehash_bucket),
+ GFP_KERNEL);
+ if (!new_hashinfo->ehash)
+ goto free_hashinfo;
+
+ new_hashinfo->ehash_mask = ehash_entries - 1;
+
+ if (inet_ehash_locks_alloc(new_hashinfo))
+ goto free_ehash;
+
+ for (i = 0; i < ehash_entries; i++)
+ INIT_HLIST_NULLS_HEAD(&new_hashinfo->ehash[i].chain, i);
+
+ new_hashinfo->bind_bucket_cachep = hashinfo->bind_bucket_cachep;
+ new_hashinfo->bhash = hashinfo->bhash;
+ new_hashinfo->bind2_bucket_cachep = hashinfo->bind2_bucket_cachep;
+ new_hashinfo->bhash2 = hashinfo->bhash2;
+ new_hashinfo->bhash_size = hashinfo->bhash_size;
+
+ new_hashinfo->lhash2_mask = hashinfo->lhash2_mask;
+ new_hashinfo->lhash2 = hashinfo->lhash2;
+
+ new_hashinfo->pernet = true;
+
+ return new_hashinfo;
+
+free_ehash:
+ kvfree(new_hashinfo->ehash);
+free_hashinfo:
+ kfree(new_hashinfo);
+err:
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(inet_pernet_hashinfo_alloc);
+
+void inet_pernet_hashinfo_free(struct inet_hashinfo *hashinfo)
+{
+ if (!hashinfo->pernet)
+ return;
+
+ inet_ehash_locks_free(hashinfo);
+ kvfree(hashinfo->ehash);
+ kfree(hashinfo);
+}
+EXPORT_SYMBOL_GPL(inet_pernet_hashinfo_free);
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 47ccc343c9fb..a5d40acde9d6 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -59,8 +59,10 @@ static void inet_twsk_kill(struct inet_timewait_sock *tw)
inet_twsk_bind_unhash(tw, hashinfo);
spin_unlock(&bhead->lock);
- if (refcount_dec_and_test(&tw->tw_dr->tw_refcount))
+ if (refcount_dec_and_test(&tw->tw_dr->tw_refcount)) {
+ inet_pernet_hashinfo_free(hashinfo);
kfree(tw->tw_dr);
+ }
inet_twsk_put(tw);
}
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 5490c285668b..03a3187c4705 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -382,6 +382,48 @@ static int proc_tcp_available_ulp(struct ctl_table *ctl,
return ret;
}
+static int proc_tcp_ehash_entries(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct net *net = container_of(table->data, struct net,
+ ipv4.sysctl_tcp_child_ehash_entries);
+ struct inet_hashinfo *hinfo = net->ipv4.tcp_death_row->hashinfo;
+ int tcp_ehash_entries;
+ struct ctl_table tbl;
+
+ tcp_ehash_entries = hinfo->ehash_mask + 1;
+
+ /* A negative number indicates that the child netns
+ * shares the global ehash.
+ */
+ if (!net_eq(net, &init_net) && !hinfo->pernet)
+ tcp_ehash_entries *= -1;
+
+ tbl.data = &tcp_ehash_entries;
+ tbl.maxlen = sizeof(int);
+
+ return proc_dointvec(&tbl, write, buffer, lenp, ppos);
+}
+
+static int proc_tcp_child_ehash_entries(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ unsigned int tcp_child_ehash_entries;
+ int ret;
+
+ ret = proc_douintvec(table, write, buffer, lenp, ppos);
+ if (!write || ret)
+ return ret;
+
+ tcp_child_ehash_entries = READ_ONCE(*(unsigned int *)table->data);
+ if (tcp_child_ehash_entries)
+ tcp_child_ehash_entries = roundup_pow_of_two(tcp_child_ehash_entries);
+
+ WRITE_ONCE(*(unsigned int *)table->data, tcp_child_ehash_entries);
+
+ return 0;
+}
+
#ifdef CONFIG_IP_ROUTE_MULTIPATH
static int proc_fib_multipath_hash_policy(struct ctl_table *table, int write,
void *buffer, size_t *lenp,
@@ -1321,6 +1363,21 @@ static struct ctl_table ipv4_net_table[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
+ {
+ .procname = "tcp_ehash_entries",
+ .data = &init_net.ipv4.sysctl_tcp_child_ehash_entries,
+ .mode = 0444,
+ .proc_handler = proc_tcp_ehash_entries,
+ },
+ {
+ .procname = "tcp_child_ehash_entries",
+ .data = &init_net.ipv4.sysctl_tcp_child_ehash_entries,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_tcp_child_ehash_entries,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_INT_MAX,
+ },
{
.procname = "udp_rmem_min",
.data = &init_net.ipv4.sysctl_udp_rmem_min,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index baf6adb723ad..f8ce673e32cb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4788,6 +4788,7 @@ void __init tcp_init(void)
INIT_HLIST_HEAD(&tcp_hashinfo.bhash2[i].chain);
}
+ tcp_hashinfo.pernet = false;
cnt = tcp_hashinfo.ehash_mask + 1;
sysctl_tcp_max_orphans = cnt / 2;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index b07930643b11..604119f46b52 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -3109,14 +3109,23 @@ static void __net_exit tcp_sk_exit(struct net *net)
if (net->ipv4.tcp_congestion_control)
bpf_module_put(net->ipv4.tcp_congestion_control,
net->ipv4.tcp_congestion_control->owner);
- if (refcount_dec_and_test(&tcp_death_row->tw_refcount))
+ if (refcount_dec_and_test(&tcp_death_row->tw_refcount)) {
+ inet_pernet_hashinfo_free(tcp_death_row->hashinfo);
kfree(tcp_death_row);
+ }
}
-static int __net_init tcp_sk_init(struct net *net)
+static void __net_init tcp_set_hashinfo(struct net *net, struct inet_hashinfo *hinfo)
{
- int cnt;
+ int ehash_entries = hinfo->ehash_mask + 1;
+ net->ipv4.tcp_death_row->hashinfo = hinfo;
+ net->ipv4.tcp_death_row->sysctl_max_tw_buckets = ehash_entries / 2;
+ net->ipv4.sysctl_max_syn_backlog = max(128, ehash_entries / 128);
+}
+
+static int __net_init tcp_sk_init(struct net *net)
+{
net->ipv4.sysctl_tcp_ecn = 2;
net->ipv4.sysctl_tcp_ecn_fallback = 1;
@@ -3145,12 +3154,10 @@ static int __net_init tcp_sk_init(struct net *net)
net->ipv4.tcp_death_row = kzalloc(sizeof(struct inet_timewait_death_row), GFP_KERNEL);
if (!net->ipv4.tcp_death_row)
return -ENOMEM;
+
refcount_set(&net->ipv4.tcp_death_row->tw_refcount, 1);
- cnt = tcp_hashinfo.ehash_mask + 1;
- net->ipv4.tcp_death_row->sysctl_max_tw_buckets = cnt / 2;
- net->ipv4.tcp_death_row->hashinfo = &tcp_hashinfo;
+ tcp_set_hashinfo(net, &tcp_hashinfo);
- net->ipv4.sysctl_max_syn_backlog = max(128, cnt / 128);
net->ipv4.sysctl_tcp_sack = 1;
net->ipv4.sysctl_tcp_window_scaling = 1;
net->ipv4.sysctl_tcp_timestamps = 1;
@@ -3206,18 +3213,46 @@ static int __net_init tcp_sk_init(struct net *net)
return 0;
}
+static int __net_init tcp_sk_init_pernet_hashinfo(struct net *net, struct net *old_net)
+{
+ struct inet_hashinfo *child_hinfo;
+ int ehash_entries;
+
+ ehash_entries = READ_ONCE(old_net->ipv4.sysctl_tcp_child_ehash_entries);
+ if (!ehash_entries)
+ goto out;
+
+ child_hinfo = inet_pernet_hashinfo_alloc(&tcp_hashinfo, ehash_entries);
+ if (child_hinfo)
+ tcp_set_hashinfo(net, child_hinfo);
+ else
+ pr_warn("Failed to allocate TCP ehash (entries: %u) "
+ "for a netns, fallback to use the global one\n",
+ ehash_entries);
+out:
+ return 0;
+}
+
static void __net_exit tcp_sk_exit_batch(struct list_head *net_exit_list)
{
+ bool purge_once = true;
struct net *net;
- inet_twsk_purge(&tcp_hashinfo, AF_INET);
+ list_for_each_entry(net, net_exit_list, exit_list) {
+ if (net->ipv4.tcp_death_row->hashinfo->pernet) {
+ inet_twsk_purge(net->ipv4.tcp_death_row->hashinfo, AF_INET);
+ } else if (purge_once) {
+ inet_twsk_purge(&tcp_hashinfo, AF_INET);
+ purge_once = false;
+ }
- list_for_each_entry(net, net_exit_list, exit_list)
tcp_fastopen_ctx_destroy(net);
+ }
}
static struct pernet_operations __net_initdata tcp_sk_ops = {
.init = tcp_sk_init,
+ .init2 = tcp_sk_init_pernet_hashinfo,
.exit = tcp_sk_exit,
.exit_batch = tcp_sk_exit_batch,
};
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 27b2fd98a2c4..19f730428720 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -2229,7 +2229,17 @@ static void __net_exit tcpv6_net_exit(struct net *net)
static void __net_exit tcpv6_net_exit_batch(struct list_head *net_exit_list)
{
- inet_twsk_purge(&tcp_hashinfo, AF_INET6);
+ bool purge_once = true;
+ struct net *net;
+
+ list_for_each_entry(net, net_exit_list, exit_list) {
+ if (net->ipv4.tcp_death_row->hashinfo->pernet) {
+ inet_twsk_purge(net->ipv4.tcp_death_row->hashinfo, AF_INET6);
+ } else if (purge_once) {
+ inet_twsk_purge(&tcp_hashinfo, AF_INET6);
+ purge_once = false;
+ }
+ }
}
static struct pernet_operations tcpv6_net_ops = {
--
2.30.2
