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Message-Id: <20231021012322.1799-1-hdanton@sina.com> Date: Sat, 21 Oct 2023 09:23:22 +0800 From: Hillf Danton <hdanton@...a.com> To: Ivan Babrou <ivan@...udflare.com> Cc: Linux Kernel Network Developers <netdev@...r.kernel.org>, kernel-team <kernel-team@...udflare.com>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: wait_for_unix_gc can cause CPU overload for well behaved programs On Fri, 20 Oct 2023 10:25:25 -0700 Ivan Babrou <ivan@...udflare.com> > > This could solve wait_for_unix_gc spinning, but it wouldn't affect > unix_gc itself, from what I understand. There would always be one > socket writer or destroyer punished by running the gc still. See what you want. The innocents are rescued by kicking a worker off. Only for thoughts. --- x/net/unix/garbage.c +++ y/net/unix/garbage.c @@ -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) @@ -185,24 +184,25 @@ static void inc_inflight_move_tail(struc list_move_tail(&u->link, &gc_candidates); } -static bool gc_in_progress; +static void __unix_gc(struct work_struct *w); +static DECLARE_WORK(unix_gc_work, __unix_gc); + #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, gc_in_progress == false); + * kick a garbage collect right now. + * + * todo s/wait_for_unix_gc/kick_unix_gc/ + */ + if (READ_ONCE(unix_tot_inflight) > UNIX_INFLIGHT_TRIGGER_GC /2) + queue_work(system_unbound_wq, &unix_gc_work); } -/* The external entry point: unix_gc() */ -void unix_gc(void) +static DEFINE_MUTEX(unix_gc_mutex); + +static void __unix_gc(struct work_struct *w) { struct sk_buff *next_skb, *skb; struct unix_sock *u; @@ -211,15 +211,10 @@ void unix_gc(void) struct list_head cursor; LIST_HEAD(not_cycle_list); + if (!mutex_trylock(&unix_gc_mutex)) + return; 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. @@ -325,11 +320,12 @@ void unix_gc(void) /* All candidates should have been detached by now. */ BUG_ON(!list_empty(&gc_candidates)); - /* 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); + mutex_unlock(&unix_gc_mutex); +} + +/* The external entry point: unix_gc() */ +void unix_gc(void) +{ + __unix_gc(NULL); } --
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