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tcp: Save unnecessary inet_twsk_purge() calls.

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While destroying netns, we call inet_twsk_purge() in tcp_sk_exit_batch()
and tcpv6_net_exit_batch() for AF_INET and AF_INET6.  These commands
trigger the kernel to walk through the potentially big ehash twice even
though the netns has no TIME_WAIT sockets.

  # ip netns add test
  # ip netns del test

  or

  # unshare -n /bin/true >/dev/null

When tw_refcount is 1, we need not call inet_twsk_purge() at least
for the net.  We can save such unneeded iterations if all netns in
net_exit_list have no TIME_WAIT sockets.  This change eliminates
the tax by the additional unshare() described in the next patch to
guarantee the per-netns ehash size.

Tested:

  # mount -t debugfs none /sys/kernel/debug/
  # echo cleanup_net > /sys/kernel/debug/tracing/set_ftrace_filter
  # echo inet_twsk_purge >> /sys/kernel/debug/tracing/set_ftrace_filter
  # echo function > /sys/kernel/debug/tracing/current_tracer
  # cat ./add_del_unshare.sh
  for i in `seq 1 40`
  do
      (for j in `seq 1 100` ; do  unshare -n /bin/true >/dev/null ; done) &
  done
  wait;
  # ./add_del_unshare.sh

Before the patch:

  # cat /sys/kernel/debug/tracing/trace_pipe
    kworker/u128:0-8       [031] ...1.   174.162765: cleanup_net <-process_one_work
    kworker/u128:0-8       [031] ...1.   174.240796: inet_twsk_purge <-cleanup_net
    kworker/u128:0-8       [032] ...1.   174.244759: inet_twsk_purge <-tcp_sk_exit_batch
    kworker/u128:0-8       [034] ...1.   174.290861: cleanup_net <-process_one_work
    kworker/u128:0-8       [039] ...1.   175.245027: inet_twsk_purge <-cleanup_net
    kworker/u128:0-8       [046] ...1.   175.290541: inet_twsk_purge <-tcp_sk_exit_batch
    kworker/u128:0-8       [037] ...1.   175.321046: cleanup_net <-process_one_work
    kworker/u128:0-8       [024] ...1.   175.941633: inet_twsk_purge <-cleanup_net
    kworker/u128:0-8       [025] ...1.   176.242539: inet_twsk_purge <-tcp_sk_exit_batch

After:

  # cat /sys/kernel/debug/tracing/trace_pipe
    kworker/u128:0-8       [038] ...1.   428.116174: cleanup_net <-process_one_work
    kworker/u128:0-8       [038] ...1.   428.262532: cleanup_net <-process_one_work
    kworker/u128:0-8       [030] ...1.   429.292645: cleanup_net <-process_one_work

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2022-09-07 18:10:21 -07:00 committed by Jakub Kicinski
parent 4461568aa4
commit edc12f032a
4 changed files with 18 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/tcp.h
View File

@ -346,6 +346,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);
void tcp_rcv_space_adjust(struct sock *sk);
int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);
void tcp_twsk_destructor(struct sock *sk);
void tcp_twsk_purge(struct list_head *net_exit_list, int family);
ssize_t tcp_splice_read(struct socket *sk, loff_t *ppos,
struct pipe_inode_info *pipe, size_t len,
unsigned int flags);

2
net/ipv4/tcp_ipv4.c
View File

@ -3206,7 +3206,7 @@ static void __net_exit tcp_sk_exit_batch(struct list_head *net_exit_list)
{
struct net *net;
inet_twsk_purge(&tcp_hashinfo, AF_INET);
tcp_twsk_purge(net_exit_list, AF_INET);
list_for_each_entry(net, net_exit_list, exit_list) {
WARN_ON_ONCE(!refcount_dec_and_test(&net->ipv4.tcp_death_row.tw_refcount));

15
net/ipv4/tcp_minisocks.c
View File

@ -347,6 +347,21 @@ void tcp_twsk_destructor(struct sock *sk)
}
EXPORT_SYMBOL_GPL(tcp_twsk_destructor);
void tcp_twsk_purge(struct list_head *net_exit_list, int family)
{
struct net *net;
list_for_each_entry(net, net_exit_list, exit_list) {
/* The last refcount is decremented in tcp_sk_exit_batch() */
if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1)
continue;
inet_twsk_purge(&tcp_hashinfo, family);
break;
}
}
EXPORT_SYMBOL_GPL(tcp_twsk_purge);
/* Warning : This function is called without sk_listener being locked.
* Be sure to read socket fields once, as their value could change under us.
*/

2
net/ipv6/tcp_ipv6.c
View File

@ -2229,7 +2229,7 @@ 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);
tcp_twsk_purge(net_exit_list, AF_INET6);
}
static struct pernet_operations tcpv6_net_ops = {