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af_unix: Try to run GC async.

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If more than 16000 inflight AF_UNIX sockets exist and the garbage
collector is not running, unix_(dgram|stream)_sendmsg() call unix_gc().
Also, they wait for unix_gc() to complete.

In unix_gc(), all inflight AF_UNIX sockets are traversed at least once,
and more if they are the GC candidate.  Thus, sendmsg() significantly
slows down with too many inflight AF_UNIX sockets.

However, if a process sends data with no AF_UNIX FD, the sendmsg() call
does not need to wait for GC.  After this change, only the process that
meets the condition below will be blocked under such a situation.

  1) cmsg contains AF_UNIX socket
  2) more than 32 AF_UNIX sent by the same user are still inflight

Note that even a sendmsg() call that does not meet the condition but has
AF_UNIX FD will be blocked later in unix_scm_to_skb() by the spinlock,
but we allow that as a bonus for sane users.

The results below are the time spent in unix_dgram_sendmsg() sending 1
byte of data with no FD 4096 times on a host where 32K inflight AF_UNIX
sockets exist.

Without series: the sane sendmsg() needs to wait gc unreasonably.

  $ sudo /usr/share/bcc/tools/funclatency -p 11165 unix_dgram_sendmsg
  Tracing 1 functions for "unix_dgram_sendmsg"... Hit Ctrl-C to end.
  ^C
       nsecs               : count     distribution
  [...]
      524288 -> 1048575    : 0        |                                        |
     1048576 -> 2097151    : 3881     |****************************************|
     2097152 -> 4194303    : 214      |**                                      |
     4194304 -> 8388607    : 1        |                                        |

  avg = 1825567 nsecs, total: 7477526027 nsecs, count: 4096

With series: the sane sendmsg() can finish much faster.

  $ sudo /usr/share/bcc/tools/funclatency -p 8702  unix_dgram_sendmsg
  Tracing 1 functions for "unix_dgram_sendmsg"... Hit Ctrl-C to end.
  ^C
       nsecs               : count     distribution
  [...]
         128 -> 255        : 0        |                                        |
         256 -> 511        : 4092     |****************************************|
         512 -> 1023       : 2        |                                        |
        1024 -> 2047       : 0        |                                        |
        2048 -> 4095       : 0        |                                        |
        4096 -> 8191       : 1        |                                        |
        8192 -> 16383      : 1        |                                        |

  avg = 410 nsecs, total: 1680510 nsecs, count: 4096

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240123170856.41348-6-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2024-01-23 09:08:56 -08:00 committed by Jakub Kicinski
parent 8b90a9f819
commit d9f21b3613
5 changed files with 29 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

12
include/net/af_unix.h
View file

@ -8,13 +8,21 @@
#include <linux/refcount.h>
#include <net/sock.h>
#if IS_ENABLED(CONFIG_UNIX)
struct unix_sock *unix_get_socket(struct file *filp);
#else
static inline struct unix_sock *unix_get_socket(struct file *filp)
{
return NULL;
}
#endif
void unix_inflight(struct user_struct *user, struct file *fp);
void unix_notinflight(struct user_struct *user, struct file *fp);
void unix_destruct_scm(struct sk_buff *skb);
void io_uring_destruct_scm(struct sk_buff *skb);
void unix_gc(void);
void wait_for_unix_gc(void);
struct unix_sock *unix_get_socket(struct file *filp);
void wait_for_unix_gc(struct scm_fp_list *fpl);
struct sock *unix_peer_get(struct sock *sk);
#define UNIX_HASH_MOD (256 - 1)

1
include/net/scm.h
View file

@ -25,6 +25,7 @@ struct scm_creds {
struct scm_fp_list {
short count;
short count_unix;
short max;
struct user_struct *user;
struct file *fp[SCM_MAX_FD];

5
net/core/scm.c
View file

@ -36,6 +36,7 @@
#include <net/compat.h>
#include <net/scm.h>
#include <net/cls_cgroup.h>
#include <net/af_unix.h>
/*
@ -85,6 +86,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
return -ENOMEM;
*fplp = fpl;
fpl->count = 0;
fpl->count_unix = 0;
fpl->max = SCM_MAX_FD;
fpl->user = NULL;
}
@ -109,6 +111,9 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
fput(file);
return -EINVAL;
}
if (unix_get_socket(file))
fpl->count_unix++;
*fpp++ = file;
fpl->count++;
}

6
net/unix/af_unix.c
View file

@ -1923,11 +1923,12 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
long timeo;
int err;
wait_for_unix_gc();
err = scm_send(sock, msg, &scm, false);
if (err < 0)
return err;
wait_for_unix_gc(scm.fp);
err = -EOPNOTSUPP;
if (msg->msg_flags&MSG_OOB)
goto out;
@ -2199,11 +2200,12 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
bool fds_sent = false;
int data_len;
wait_for_unix_gc();
err = scm_send(sock, msg, &scm, false);
if (err < 0)
return err;
wait_for_unix_gc(scm.fp);
err = -EOPNOTSUPP;
if (msg->msg_flags & MSG_OOB) {
#if IS_ENABLED(CONFIG_AF_UNIX_OOB)

10
net/unix/garbage.c
View file

@ -311,8 +311,9 @@ void unix_gc(void)
}
#define UNIX_INFLIGHT_TRIGGER_GC 16000
#define UNIX_INFLIGHT_SANE_USER (SCM_MAX_FD * 8)
void wait_for_unix_gc(void)
void wait_for_unix_gc(struct scm_fp_list *fpl)
{
/* If number of inflight sockets is insane,
* force a garbage collect right now.
@ -324,6 +325,13 @@ void wait_for_unix_gc(void)
!READ_ONCE(gc_in_progress))
unix_gc();
/* Penalise users who want to send AF_UNIX sockets
* but whose sockets have not been received yet.
*/
if (!fpl || !fpl->count_unix ||
READ_ONCE(fpl->user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
return;
if (READ_ONCE(gc_in_progress))
flush_work(&unix_gc_work);
}