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Date: Fri, 17 Jun 2022 10:52:15 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <aams@...zon.com>, <davem@...emloft.net>, <kuba@...nel.org>,
<kuni1840@...il.com>, <kuniyu@...zon.com>,
<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v1 net-next 3/6] af_unix: Define a per-netns hash table.
From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 17 Jun 2022 10:00:25 +0200
> On Fri, Jun 17, 2022 at 8:57 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > From: Eric Dumazet <edumazet@...gle.com>
> > Date: Fri, 17 Jun 2022 08:08:32 +0200
> > > On Fri, Jun 17, 2022 at 7:34 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > > >
> > > > From: Eric Dumazet <edumazet@...gle.com>
> > > > Date: Fri, 17 Jun 2022 06:23:37 +0200
> > > > > On Fri, Jun 17, 2022 at 1:48 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > > > > >
> > > > > > This commit adds a per netns hash table for AF_UNIX.
> > > > > >
> > > > > > Note that its size is fixed as UNIX_HASH_SIZE for now.
> > > > > >
> > > > >
> > > > > Note: Please include memory costs for this table, including when LOCKDEP is on.
> > > >
> > > > I'm sorry but I'm not quite sure.
> > > > Do you mean the table should have the size as member of its struct?
> > > > Could you elaborate on memory costs and LOCKDEP?
> > >
> > > I am saying that instead of two separate arrays, you are now using one
> > > array, with holes in the structure
> > >
> > > Without LOCKDEP, sizeof(spinlock_t) is 4.
> > > With LOCKDEP, sizeof(spinlock_t) is bigger.
> > >
> > > So we are trading some costs of having two shared dense arrays, and
> > > having per-netns hash tables.
> > >
> > > It would be nice to mention this trade off in the changelog, because
> > > some hosts have thousands of netns and few af_unix sockets :/
> >
> > Thank you for explanation in detail!
> > I'm on the same page.
> > How about having separate arrays like this in per-netns struct?
> >
> > struct unix_table {
> > spinlock_t *locks;
> > list_head *buckets;
> > }
>
> Are we sure we need per-netns locks ?
>
> I would think that sharing 256 spinlocks would be just fine, even on
> hosts with more than 256 cpus.
I ran the test written on the last patch with three kernels 10 times
for each:
1) global locks and hash table
1m 38s ~ 1m 43s
2) per-netns locks and hash tables (two dense arrays version)
11s
3) global locks and per-netns hash tables
15s
As you thought, the length of list has larger impact than lock contention.
But on a host with 10 cpus per-netns, per-netns locks are faster than
shared one.
What do you think about this trade-off?
> > > > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > > > > > ---
> > > > > > include/net/af_unix.h | 5 +++++
> > > > > > include/net/netns/unix.h | 2 ++
> > > > > > net/unix/af_unix.c | 40 ++++++++++++++++++++++++++++++++++------
> > > > > > 3 files changed, 41 insertions(+), 6 deletions(-)
> > > > > >
> > > > > > diff --git a/include/net/af_unix.h b/include/net/af_unix.h
> > > > > > index acb56e463db1..0a17e49af0c9 100644
> > > > > > --- a/include/net/af_unix.h
> > > > > > +++ b/include/net/af_unix.h
> > > > > > @@ -24,6 +24,11 @@ extern unsigned int unix_tot_inflight;
> > > > > > extern spinlock_t unix_table_locks[UNIX_HASH_SIZE];
> > > > > > extern struct hlist_head unix_socket_table[UNIX_HASH_SIZE];
> > > > > >
> > > > > > +struct unix_hashbucket {
> > > > > > + spinlock_t lock;
> > > > > > + struct hlist_head head;
> > > > > > +};
> > > > > > +
> > > > > > struct unix_address {
> > > > > > refcount_t refcnt;
> > > > > > int len;
> > > > > > diff --git a/include/net/netns/unix.h b/include/net/netns/unix.h
> > > > > > index 91a3d7e39198..975c4e3f8a5b 100644
> > > > > > --- a/include/net/netns/unix.h
> > > > > > +++ b/include/net/netns/unix.h
> > > > > > @@ -5,8 +5,10 @@
> > > > > > #ifndef __NETNS_UNIX_H__
> > > > > > #define __NETNS_UNIX_H__
> > > > > >
> > > > > > +struct unix_hashbucket;
> > > > > > struct ctl_table_header;
> > > > > > struct netns_unix {
> > > > > > + struct unix_hashbucket *hash;
> > > > > > int sysctl_max_dgram_qlen;
> > > > > > struct ctl_table_header *ctl;
> > > > > > };
> > > > > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > > > > > index c0804ae9c96a..3c07702e2349 100644
> > > > > > --- a/net/unix/af_unix.c
> > > > > > +++ b/net/unix/af_unix.c
> > > > > > @@ -3559,7 +3559,7 @@ static const struct net_proto_family unix_family_ops = {
> > > > > >
> > > > > > static int __net_init unix_net_init(struct net *net)
> > > > > > {
> > > > > > - int error = -ENOMEM;
> > > > > > + int i;
> > > > > >
> > > > > > net->unx.sysctl_max_dgram_qlen = 10;
> > > > > > if (unix_sysctl_register(net))
> > > > > > @@ -3567,18 +3567,35 @@ static int __net_init unix_net_init(struct net *net)
> > > > > >
> > > > > > #ifdef CONFIG_PROC_FS
> > > > > > if (!proc_create_net("unix", 0, net->proc_net, &unix_seq_ops,
> > > > > > - sizeof(struct seq_net_private))) {
> > > > > > - unix_sysctl_unregister(net);
> > > > > > - goto out;
> > > > > > + sizeof(struct seq_net_private)))
> > > > > > + goto err_sysctl;
> > > > > > +#endif
> > > > > > +
> > > > > > + net->unx.hash = kmalloc(sizeof(struct unix_hashbucket) * UNIX_HASH_SIZE,
> > > > > > + GFP_KERNEL);
> > > > >
> > > > > This will fail under memory pressure.
> > > > >
> > > > > Prefer kvmalloc_array()
> > > >
> > > > Thank you for feedback!
> > > > I will use it in v2.
> > > >
> > > >
> > > > > > + if (!net->unx.hash)
> > > > > > + goto err_proc;
> > > > > > +
> > > > > > + for (i = 0; i < UNIX_HASH_SIZE; i++) {
> > > > > > + INIT_HLIST_HEAD(&net->unx.hash[i].head);
> > > > > > + spin_lock_init(&net->unx.hash[i].lock);
> > > > > > }
> > > > > > +
> > > > > > + return 0;
> > > > > > +
> > > > > > +err_proc:
> > > > > > +#ifdef CONFIG_PROC_FS
> > > > > > + remove_proc_entry("unix", net->proc_net);
> > > > > > #endif
> > > > > > - error = 0;
> > > > > > +err_sysctl:
> > > > > > + unix_sysctl_unregister(net);
> > > > > > out:
> > > > > > - return error;
> > > > > > + return -ENOMEM;
> > > > > > }
> > > > > >
> > > > > > static void __net_exit unix_net_exit(struct net *net)
> > > > > > {
> > > > > > + kfree(net->unx.hash);
> > > > >
> > > > > kvfree()
> > > > >
> > > > > > unix_sysctl_unregister(net);
> > > > > > remove_proc_entry("unix", net->proc_net);
> > > > > > }
> > > > > > @@ -3666,6 +3683,16 @@ static int __init af_unix_init(void)
> > > > > >
> > > > > > BUILD_BUG_ON(sizeof(struct unix_skb_parms) > sizeof_field(struct sk_buff, cb));
> > > > > >
> > > > > > + init_net.unx.hash = kmalloc(sizeof(struct unix_hashbucket) * UNIX_HASH_SIZE,
> > > > > > + GFP_KERNEL);
> > > > >
> > > > > Why are you allocating the hash table twice ? It should be done
> > > > > already in unix_net_init() ?
> > > >
> > > > Ah sorry, just my mistake.
> > > > I'll remove this alloc/free part.
> > > >
> > > >
> > > > > > + if (!init_net.unx.hash)
> > > > > > + goto out;
> > > > > > +
> > > > > > + for (i = 0; i < UNIX_HASH_SIZE; i++) {
> > > > > > + INIT_HLIST_HEAD(&init_net.unx.hash[i].head);
> > > > > > + spin_lock_init(&init_net.unx.hash[i].lock);
> > > > > > + }
> > > > > > +
> > > > > > for (i = 0; i < UNIX_HASH_SIZE; i++)
> > > > > > spin_lock_init(&unix_table_locks[i]);
> > > > > >
> > > > > > @@ -3699,6 +3726,7 @@ static void __exit af_unix_exit(void)
> > > > > > proto_unregister(&unix_dgram_proto);
> > > > > > proto_unregister(&unix_stream_proto);
> > > > > > unregister_pernet_subsys(&unix_net_ops);
> > > > > > + kfree(init_net.unx.hash);
> > > > >
> > > > > Not needed.
> > > > >
> > > > > > }
> > > > > >
> > > > > > /* Earlier than device_initcall() so that other drivers invoking
> > > > > > --
> > > > > > 2.30.2
> > > > > >
> > > >
> > > >
> > > > Best regards,
> > > > Kuniyuki
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