iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

af_unix: Run GC on only one CPU.

Browse Source 
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.

There is a small window to invoke multiple unix_gc() instances, which
will then be blocked by the same spinlock except for one.

Let's convert unix_gc() to use struct work so that it will not consume
CPUs unnecessarily.

Note WRITE_ONCE(gc_in_progress, true) is moved before running GC.
If we leave the WRITE_ONCE() as is and use the following test to
call flush_work(), a process might not call it.

    CPU 0                                     CPU 1
    ---                                       ---
                                              start work and call __unix_gc()
    if (work_pending(&unix_gc_work) ||        <-- false
        READ_ONCE(gc_in_progress))            <-- false
            flush_work();                     <-- missed!
	                                      WRITE_ONCE(gc_in_progress, true)

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240123170856.41348-5-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2024-01-23 09:08:55 -08:00 committed by Jakub Kicinski
parent 5b17307bd0
commit 8b90a9f819
1 changed files with 27 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

54
net/unix/garbage.c
View File

@ -86,7 +86,6 @@
/* Internal data structures and random procedures: */
static LIST_HEAD(gc_candidates);
static DECLARE_WAIT_QUEUE_HEAD(unix_gc_wait);
static void scan_inflight(struct sock *x, void (*func)(struct unix_sock *),
struct sk_buff_head *hitlist)
@ -182,23 +181,8 @@ static void inc_inflight_move_tail(struct unix_sock *u)
}
static bool gc_in_progress;
#define UNIX_INFLIGHT_TRIGGER_GC 16000
void wait_for_unix_gc(void)
{
/* If number of inflight sockets is insane,
* force a garbage collect right now.
* Paired with the WRITE_ONCE() in unix_inflight(),
* unix_notinflight() and gc_in_progress().
*/
if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
!READ_ONCE(gc_in_progress))
unix_gc();
wait_event(unix_gc_wait, !READ_ONCE(gc_in_progress));
}
/* The external entry point: unix_gc() */
void unix_gc(void)
static void __unix_gc(struct work_struct *work)
{
struct sk_buff *next_skb, *skb;
struct unix_sock *u;
@ -209,13 +193,6 @@ void unix_gc(void)
spin_lock(&unix_gc_lock);
/* Avoid a recursive GC. */
if (gc_in_progress)
goto out;
/* Paired with READ_ONCE() in wait_for_unix_gc(). */
WRITE_ONCE(gc_in_progress, true);
/* First, select candidates for garbage collection. Only
* in-flight sockets are considered, and from those only ones
* which don't have any external reference.
@ -322,8 +299,31 @@ void unix_gc(void)
/* Paired with READ_ONCE() in wait_for_unix_gc(). */
WRITE_ONCE(gc_in_progress, false);
wake_up(&unix_gc_wait);
out:
spin_unlock(&unix_gc_lock);
}
static DECLARE_WORK(unix_gc_work, __unix_gc);
void unix_gc(void)
{
WRITE_ONCE(gc_in_progress, true);
queue_work(system_unbound_wq, &unix_gc_work);
}
#define UNIX_INFLIGHT_TRIGGER_GC 16000
void wait_for_unix_gc(void)
{
/* If number of inflight sockets is insane,
* force a garbage collect right now.
*
* Paired with the WRITE_ONCE() in unix_inflight(),
* unix_notinflight(), and __unix_gc().
*/
if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC &&
!READ_ONCE(gc_in_progress))
unix_gc();
if (READ_ONCE(gc_in_progress))
flush_work(&unix_gc_work);
}