2 * net/sched/sch_fq.c Fair Queue Packet Scheduler (per flow pacing)
4 * Copyright (C) 2013-2015 Eric Dumazet <edumazet@google.com>
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
11 * Meant to be mostly used for locally generated traffic :
12 * Fast classification depends on skb->sk being set before reaching us.
13 * If not, (router workload), we use rxhash as fallback, with 32 bits wide hash.
14 * All packets belonging to a socket are considered as a 'flow'.
16 * Flows are dynamically allocated and stored in a hash table of RB trees
17 * They are also part of one Round Robin 'queues' (new or old flows)
19 * Burst avoidance (aka pacing) capability :
21 * Transport (eg TCP) can set in sk->sk_pacing_rate a rate, enqueue a
22 * bunch of packets, and this packet scheduler adds delay between
23 * packets to respect rate limitation.
26 * - lookup one RB tree (out of 1024 or more) to find the flow.
27 * If non existent flow, create it, add it to the tree.
28 * Add skb to the per flow list of skb (fifo).
29 * - Use a special fifo for high prio packets
31 * dequeue() : serves flows in Round Robin
32 * Note : When a flow becomes empty, we do not immediately remove it from
33 * rb trees, for performance reasons (its expected to send additional packets,
34 * or SLAB cache will reuse socket for another flow)
37 #include <linux/module.h>
38 #include <linux/types.h>
39 #include <linux/kernel.h>
40 #include <linux/jiffies.h>
41 #include <linux/string.h>
43 #include <linux/errno.h>
44 #include <linux/init.h>
45 #include <linux/skbuff.h>
46 #include <linux/slab.h>
47 #include <linux/rbtree.h>
48 #include <linux/hash.h>
49 #include <linux/prefetch.h>
50 #include <linux/vmalloc.h>
51 #include <net/netlink.h>
52 #include <net/pkt_sched.h>
54 #include <net/tcp_states.h>
58 * Per flow structure, dynamically allocated
61 struct sk_buff *head; /* list of skbs for this flow : first skb */
63 struct sk_buff *tail; /* last skb in the list */
64 unsigned long age; /* jiffies when flow was emptied, for gc */
66 struct rb_node fq_node; /* anchor in fq_root[] trees */
68 int qlen; /* number of packets in flow queue */
70 u32 socket_hash; /* sk_hash */
71 struct fq_flow *next; /* next pointer in RR lists, or &detached */
73 struct rb_node rate_node; /* anchor in q->delayed tree */
78 struct fq_flow *first;
82 struct fq_sched_data {
83 struct fq_flow_head new_flows;
85 struct fq_flow_head old_flows;
87 struct rb_root delayed; /* for rate limited flows */
88 u64 time_next_delayed_flow;
89 unsigned long unthrottle_latency_ns;
91 struct fq_flow internal; /* for non classified or high prio packets */
94 u32 flow_refill_delay;
95 u32 flow_max_rate; /* optional max rate per flow */
96 u32 flow_plimit; /* max packets per flow */
97 u32 orphan_mask; /* mask for orphaned skb */
98 u32 low_rate_threshold;
99 struct rb_root *fq_root;
108 u64 stat_internal_packets;
109 u64 stat_tcp_retrans;
111 u64 stat_flows_plimit;
112 u64 stat_pkts_too_long;
113 u64 stat_allocation_errors;
114 struct qdisc_watchdog watchdog;
117 /* special value to mark a detached flow (not on old/new list) */
118 static struct fq_flow detached, throttled;
120 static void fq_flow_set_detached(struct fq_flow *f)
126 static bool fq_flow_is_detached(const struct fq_flow *f)
128 return f->next == &detached;
131 static void fq_flow_set_throttled(struct fq_sched_data *q, struct fq_flow *f)
133 struct rb_node **p = &q->delayed.rb_node, *parent = NULL;
139 aux = rb_entry(parent, struct fq_flow, rate_node);
140 if (f->time_next_packet >= aux->time_next_packet)
141 p = &parent->rb_right;
143 p = &parent->rb_left;
145 rb_link_node(&f->rate_node, parent, p);
146 rb_insert_color(&f->rate_node, &q->delayed);
147 q->throttled_flows++;
150 f->next = &throttled;
151 if (q->time_next_delayed_flow > f->time_next_packet)
152 q->time_next_delayed_flow = f->time_next_packet;
156 static struct kmem_cache *fq_flow_cachep __read_mostly;
158 static void fq_flow_add_tail(struct fq_flow_head *head, struct fq_flow *flow)
161 head->last->next = flow;
168 /* limit number of collected flows per round */
170 #define FQ_GC_AGE (3*HZ)
172 static bool fq_gc_candidate(const struct fq_flow *f)
174 return fq_flow_is_detached(f) &&
175 time_after(jiffies, f->age + FQ_GC_AGE);
178 static void fq_gc(struct fq_sched_data *q,
179 struct rb_root *root,
182 struct fq_flow *f, *tofree[FQ_GC_MAX];
183 struct rb_node **p, *parent;
191 f = rb_entry(parent, struct fq_flow, fq_node);
195 if (fq_gc_candidate(f)) {
197 if (fcnt == FQ_GC_MAX)
202 p = &parent->rb_right;
204 p = &parent->rb_left;
208 q->inactive_flows -= fcnt;
209 q->stat_gc_flows += fcnt;
211 struct fq_flow *f = tofree[--fcnt];
213 rb_erase(&f->fq_node, root);
214 kmem_cache_free(fq_flow_cachep, f);
218 static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q)
220 struct rb_node **p, *parent;
221 struct sock *sk = skb->sk;
222 struct rb_root *root;
225 /* warning: no starvation prevention... */
226 if (unlikely((skb->priority & TC_PRIO_MAX) == TC_PRIO_CONTROL))
229 /* SYNACK messages are attached to a TCP_NEW_SYN_RECV request socket
230 * or a listener (SYNCOOKIE mode)
231 * 1) request sockets are not full blown,
232 * they do not contain sk_pacing_rate
233 * 2) They are not part of a 'flow' yet
234 * 3) We do not want to rate limit them (eg SYNFLOOD attack),
235 * especially if the listener set SO_MAX_PACING_RATE
236 * 4) We pretend they are orphaned
238 if (!sk || sk_listener(sk)) {
239 unsigned long hash = skb_get_hash(skb) & q->orphan_mask;
241 /* By forcing low order bit to 1, we make sure to not
242 * collide with a local flow (socket pointers are word aligned)
244 sk = (struct sock *)((hash << 1) | 1UL);
248 root = &q->fq_root[hash_ptr(sk, q->fq_trees_log)];
250 if (q->flows >= (2U << q->fq_trees_log) &&
251 q->inactive_flows > q->flows/2)
259 f = rb_entry(parent, struct fq_flow, fq_node);
261 /* socket might have been reallocated, so check
262 * if its sk_hash is the same.
263 * It not, we need to refill credit with
266 if (unlikely(skb->sk &&
267 f->socket_hash != sk->sk_hash)) {
268 f->credit = q->initial_quantum;
269 f->socket_hash = sk->sk_hash;
270 f->time_next_packet = 0ULL;
275 p = &parent->rb_right;
277 p = &parent->rb_left;
280 f = kmem_cache_zalloc(fq_flow_cachep, GFP_ATOMIC | __GFP_NOWARN);
282 q->stat_allocation_errors++;
285 fq_flow_set_detached(f);
288 f->socket_hash = sk->sk_hash;
289 f->credit = q->initial_quantum;
291 rb_link_node(&f->fq_node, parent, p);
292 rb_insert_color(&f->fq_node, root);
300 /* remove one skb from head of flow queue */
301 static struct sk_buff *fq_dequeue_head(struct Qdisc *sch, struct fq_flow *flow)
303 struct sk_buff *skb = flow->head;
306 flow->head = skb->next;
309 qdisc_qstats_backlog_dec(sch, skb);
315 /* We might add in the future detection of retransmits
316 * For the time being, just return false
318 static bool skb_is_retransmit(struct sk_buff *skb)
323 /* add skb to flow queue
324 * flow queue is a linked list, kind of FIFO, except for TCP retransmits
325 * We special case tcp retransmits to be transmitted before other packets.
326 * We rely on fact that TCP retransmits are unlikely, so we do not waste
327 * a separate queue or a pointer.
328 * head-> [retrans pkt 1]
333 * tail-> [ normal pkt 4]
335 static void flow_queue_add(struct fq_flow *flow, struct sk_buff *skb)
337 struct sk_buff *prev, *head = flow->head;
345 if (likely(!skb_is_retransmit(skb))) {
346 flow->tail->next = skb;
351 /* This skb is a tcp retransmit,
352 * find the last retrans packet in the queue
355 while (skb_is_retransmit(head)) {
361 if (!prev) { /* no rtx packet in queue, become the new head */
362 skb->next = flow->head;
365 if (prev == flow->tail)
368 skb->next = prev->next;
373 static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
374 struct sk_buff **to_free)
376 struct fq_sched_data *q = qdisc_priv(sch);
379 if (unlikely(sch->q.qlen >= sch->limit))
380 return qdisc_drop(skb, sch, to_free);
382 f = fq_classify(skb, q);
383 if (unlikely(f->qlen >= q->flow_plimit && f != &q->internal)) {
384 q->stat_flows_plimit++;
385 return qdisc_drop(skb, sch, to_free);
389 if (skb_is_retransmit(skb))
390 q->stat_tcp_retrans++;
391 qdisc_qstats_backlog_inc(sch, skb);
392 if (fq_flow_is_detached(f)) {
393 struct sock *sk = skb->sk;
395 fq_flow_add_tail(&q->new_flows, f);
396 if (time_after(jiffies, f->age + q->flow_refill_delay))
397 f->credit = max_t(u32, f->credit, q->quantum);
398 if (sk && q->rate_enable) {
399 if (unlikely(smp_load_acquire(&sk->sk_pacing_status) !=
401 smp_store_release(&sk->sk_pacing_status,
407 /* Note: this overwrites f->age */
408 flow_queue_add(f, skb);
410 if (unlikely(f == &q->internal)) {
411 q->stat_internal_packets++;
415 return NET_XMIT_SUCCESS;
418 static void fq_check_throttled(struct fq_sched_data *q, u64 now)
420 unsigned long sample;
423 if (q->time_next_delayed_flow > now)
426 /* Update unthrottle latency EWMA.
427 * This is cheap and can help diagnosing timer/latency problems.
429 sample = (unsigned long)(now - q->time_next_delayed_flow);
430 q->unthrottle_latency_ns -= q->unthrottle_latency_ns >> 3;
431 q->unthrottle_latency_ns += sample >> 3;
433 q->time_next_delayed_flow = ~0ULL;
434 while ((p = rb_first(&q->delayed)) != NULL) {
435 struct fq_flow *f = rb_entry(p, struct fq_flow, rate_node);
437 if (f->time_next_packet > now) {
438 q->time_next_delayed_flow = f->time_next_packet;
441 rb_erase(p, &q->delayed);
442 q->throttled_flows--;
443 fq_flow_add_tail(&q->old_flows, f);
447 static struct sk_buff *fq_dequeue(struct Qdisc *sch)
449 struct fq_sched_data *q = qdisc_priv(sch);
450 u64 now = ktime_get_ns();
451 struct fq_flow_head *head;
456 skb = fq_dequeue_head(sch, &q->internal);
459 fq_check_throttled(q, now);
461 head = &q->new_flows;
463 head = &q->old_flows;
465 if (q->time_next_delayed_flow != ~0ULL)
466 qdisc_watchdog_schedule_ns(&q->watchdog,
467 q->time_next_delayed_flow);
473 if (f->credit <= 0) {
474 f->credit += q->quantum;
475 head->first = f->next;
476 fq_flow_add_tail(&q->old_flows, f);
481 if (unlikely(skb && now < f->time_next_packet &&
482 !skb_is_tcp_pure_ack(skb))) {
483 head->first = f->next;
484 fq_flow_set_throttled(q, f);
488 skb = fq_dequeue_head(sch, f);
490 head->first = f->next;
491 /* force a pass through old_flows to prevent starvation */
492 if ((head == &q->new_flows) && q->old_flows.first) {
493 fq_flow_add_tail(&q->old_flows, f);
495 fq_flow_set_detached(f);
501 f->credit -= qdisc_pkt_len(skb);
506 /* Do not pace locally generated ack packets */
507 if (skb_is_tcp_pure_ack(skb))
510 rate = q->flow_max_rate;
512 rate = min(skb->sk->sk_pacing_rate, rate);
514 if (rate <= q->low_rate_threshold) {
516 plen = qdisc_pkt_len(skb);
518 plen = max(qdisc_pkt_len(skb), q->quantum);
523 u64 len = (u64)plen * NSEC_PER_SEC;
527 /* Since socket rate can change later,
528 * clamp the delay to 1 second.
529 * Really, providers of too big packets should be fixed !
531 if (unlikely(len > NSEC_PER_SEC)) {
533 q->stat_pkts_too_long++;
535 /* Account for schedule/timers drifts.
536 * f->time_next_packet was set when prior packet was sent,
537 * and current time (@now) can be too late by tens of us.
539 if (f->time_next_packet)
540 len -= min(len/2, now - f->time_next_packet);
541 f->time_next_packet = now + len;
544 qdisc_bstats_update(sch, skb);
548 static void fq_flow_purge(struct fq_flow *flow)
550 rtnl_kfree_skbs(flow->head, flow->tail);
555 static void fq_reset(struct Qdisc *sch)
557 struct fq_sched_data *q = qdisc_priv(sch);
558 struct rb_root *root;
564 sch->qstats.backlog = 0;
566 fq_flow_purge(&q->internal);
571 for (idx = 0; idx < (1U << q->fq_trees_log); idx++) {
572 root = &q->fq_root[idx];
573 while ((p = rb_first(root)) != NULL) {
574 f = rb_entry(p, struct fq_flow, fq_node);
579 kmem_cache_free(fq_flow_cachep, f);
582 q->new_flows.first = NULL;
583 q->old_flows.first = NULL;
584 q->delayed = RB_ROOT;
586 q->inactive_flows = 0;
587 q->throttled_flows = 0;
590 static void fq_rehash(struct fq_sched_data *q,
591 struct rb_root *old_array, u32 old_log,
592 struct rb_root *new_array, u32 new_log)
594 struct rb_node *op, **np, *parent;
595 struct rb_root *oroot, *nroot;
596 struct fq_flow *of, *nf;
600 for (idx = 0; idx < (1U << old_log); idx++) {
601 oroot = &old_array[idx];
602 while ((op = rb_first(oroot)) != NULL) {
604 of = rb_entry(op, struct fq_flow, fq_node);
605 if (fq_gc_candidate(of)) {
607 kmem_cache_free(fq_flow_cachep, of);
610 nroot = &new_array[hash_ptr(of->sk, new_log)];
612 np = &nroot->rb_node;
617 nf = rb_entry(parent, struct fq_flow, fq_node);
618 BUG_ON(nf->sk == of->sk);
621 np = &parent->rb_right;
623 np = &parent->rb_left;
626 rb_link_node(&of->fq_node, parent, np);
627 rb_insert_color(&of->fq_node, nroot);
631 q->inactive_flows -= fcnt;
632 q->stat_gc_flows += fcnt;
635 static void fq_free(void *addr)
640 static int fq_resize(struct Qdisc *sch, u32 log)
642 struct fq_sched_data *q = qdisc_priv(sch);
643 struct rb_root *array;
647 if (q->fq_root && log == q->fq_trees_log)
650 /* If XPS was setup, we can allocate memory on right NUMA node */
651 array = kvmalloc_node(sizeof(struct rb_root) << log, GFP_KERNEL | __GFP_RETRY_MAYFAIL,
652 netdev_queue_numa_node_read(sch->dev_queue));
656 for (idx = 0; idx < (1U << log); idx++)
657 array[idx] = RB_ROOT;
661 old_fq_root = q->fq_root;
663 fq_rehash(q, old_fq_root, q->fq_trees_log, array, log);
666 q->fq_trees_log = log;
668 sch_tree_unlock(sch);
670 fq_free(old_fq_root);
675 static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
676 [TCA_FQ_PLIMIT] = { .type = NLA_U32 },
677 [TCA_FQ_FLOW_PLIMIT] = { .type = NLA_U32 },
678 [TCA_FQ_QUANTUM] = { .type = NLA_U32 },
679 [TCA_FQ_INITIAL_QUANTUM] = { .type = NLA_U32 },
680 [TCA_FQ_RATE_ENABLE] = { .type = NLA_U32 },
681 [TCA_FQ_FLOW_DEFAULT_RATE] = { .type = NLA_U32 },
682 [TCA_FQ_FLOW_MAX_RATE] = { .type = NLA_U32 },
683 [TCA_FQ_BUCKETS_LOG] = { .type = NLA_U32 },
684 [TCA_FQ_FLOW_REFILL_DELAY] = { .type = NLA_U32 },
685 [TCA_FQ_LOW_RATE_THRESHOLD] = { .type = NLA_U32 },
688 static int fq_change(struct Qdisc *sch, struct nlattr *opt)
690 struct fq_sched_data *q = qdisc_priv(sch);
691 struct nlattr *tb[TCA_FQ_MAX + 1];
692 int err, drop_count = 0;
693 unsigned drop_len = 0;
699 err = nla_parse_nested(tb, TCA_FQ_MAX, opt, fq_policy, NULL);
705 fq_log = q->fq_trees_log;
707 if (tb[TCA_FQ_BUCKETS_LOG]) {
708 u32 nval = nla_get_u32(tb[TCA_FQ_BUCKETS_LOG]);
710 if (nval >= 1 && nval <= ilog2(256*1024))
715 if (tb[TCA_FQ_PLIMIT])
716 sch->limit = nla_get_u32(tb[TCA_FQ_PLIMIT]);
718 if (tb[TCA_FQ_FLOW_PLIMIT])
719 q->flow_plimit = nla_get_u32(tb[TCA_FQ_FLOW_PLIMIT]);
721 if (tb[TCA_FQ_QUANTUM]) {
722 u32 quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);
725 q->quantum = quantum;
730 if (tb[TCA_FQ_INITIAL_QUANTUM])
731 q->initial_quantum = nla_get_u32(tb[TCA_FQ_INITIAL_QUANTUM]);
733 if (tb[TCA_FQ_FLOW_DEFAULT_RATE])
734 pr_warn_ratelimited("sch_fq: defrate %u ignored.\n",
735 nla_get_u32(tb[TCA_FQ_FLOW_DEFAULT_RATE]));
737 if (tb[TCA_FQ_FLOW_MAX_RATE])
738 q->flow_max_rate = nla_get_u32(tb[TCA_FQ_FLOW_MAX_RATE]);
740 if (tb[TCA_FQ_LOW_RATE_THRESHOLD])
741 q->low_rate_threshold =
742 nla_get_u32(tb[TCA_FQ_LOW_RATE_THRESHOLD]);
744 if (tb[TCA_FQ_RATE_ENABLE]) {
745 u32 enable = nla_get_u32(tb[TCA_FQ_RATE_ENABLE]);
748 q->rate_enable = enable;
753 if (tb[TCA_FQ_FLOW_REFILL_DELAY]) {
754 u32 usecs_delay = nla_get_u32(tb[TCA_FQ_FLOW_REFILL_DELAY]) ;
756 q->flow_refill_delay = usecs_to_jiffies(usecs_delay);
759 if (tb[TCA_FQ_ORPHAN_MASK])
760 q->orphan_mask = nla_get_u32(tb[TCA_FQ_ORPHAN_MASK]);
763 sch_tree_unlock(sch);
764 err = fq_resize(sch, fq_log);
767 while (sch->q.qlen > sch->limit) {
768 struct sk_buff *skb = fq_dequeue(sch);
772 drop_len += qdisc_pkt_len(skb);
773 rtnl_kfree_skbs(skb, skb);
776 qdisc_tree_reduce_backlog(sch, drop_count, drop_len);
778 sch_tree_unlock(sch);
782 static void fq_destroy(struct Qdisc *sch)
784 struct fq_sched_data *q = qdisc_priv(sch);
788 qdisc_watchdog_cancel(&q->watchdog);
791 static int fq_init(struct Qdisc *sch, struct nlattr *opt)
793 struct fq_sched_data *q = qdisc_priv(sch);
797 q->flow_plimit = 100;
798 q->quantum = 2 * psched_mtu(qdisc_dev(sch));
799 q->initial_quantum = 10 * psched_mtu(qdisc_dev(sch));
800 q->flow_refill_delay = msecs_to_jiffies(40);
801 q->flow_max_rate = ~0U;
802 q->time_next_delayed_flow = ~0ULL;
804 q->new_flows.first = NULL;
805 q->old_flows.first = NULL;
806 q->delayed = RB_ROOT;
808 q->fq_trees_log = ilog2(1024);
809 q->orphan_mask = 1024 - 1;
810 q->low_rate_threshold = 550000 / 8;
811 qdisc_watchdog_init(&q->watchdog, sch);
814 err = fq_change(sch, opt);
816 err = fq_resize(sch, q->fq_trees_log);
821 static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
823 struct fq_sched_data *q = qdisc_priv(sch);
826 opts = nla_nest_start(skb, TCA_OPTIONS);
828 goto nla_put_failure;
830 /* TCA_FQ_FLOW_DEFAULT_RATE is not used anymore */
832 if (nla_put_u32(skb, TCA_FQ_PLIMIT, sch->limit) ||
833 nla_put_u32(skb, TCA_FQ_FLOW_PLIMIT, q->flow_plimit) ||
834 nla_put_u32(skb, TCA_FQ_QUANTUM, q->quantum) ||
835 nla_put_u32(skb, TCA_FQ_INITIAL_QUANTUM, q->initial_quantum) ||
836 nla_put_u32(skb, TCA_FQ_RATE_ENABLE, q->rate_enable) ||
837 nla_put_u32(skb, TCA_FQ_FLOW_MAX_RATE, q->flow_max_rate) ||
838 nla_put_u32(skb, TCA_FQ_FLOW_REFILL_DELAY,
839 jiffies_to_usecs(q->flow_refill_delay)) ||
840 nla_put_u32(skb, TCA_FQ_ORPHAN_MASK, q->orphan_mask) ||
841 nla_put_u32(skb, TCA_FQ_LOW_RATE_THRESHOLD,
842 q->low_rate_threshold) ||
843 nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log))
844 goto nla_put_failure;
846 return nla_nest_end(skb, opts);
852 static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
854 struct fq_sched_data *q = qdisc_priv(sch);
855 struct tc_fq_qd_stats st;
859 st.gc_flows = q->stat_gc_flows;
860 st.highprio_packets = q->stat_internal_packets;
861 st.tcp_retrans = q->stat_tcp_retrans;
862 st.throttled = q->stat_throttled;
863 st.flows_plimit = q->stat_flows_plimit;
864 st.pkts_too_long = q->stat_pkts_too_long;
865 st.allocation_errors = q->stat_allocation_errors;
866 st.time_next_delayed_flow = q->time_next_delayed_flow - ktime_get_ns();
868 st.inactive_flows = q->inactive_flows;
869 st.throttled_flows = q->throttled_flows;
870 st.unthrottle_latency_ns = min_t(unsigned long,
871 q->unthrottle_latency_ns, ~0U);
872 sch_tree_unlock(sch);
874 return gnet_stats_copy_app(d, &st, sizeof(st));
877 static struct Qdisc_ops fq_qdisc_ops __read_mostly = {
879 .priv_size = sizeof(struct fq_sched_data),
881 .enqueue = fq_enqueue,
882 .dequeue = fq_dequeue,
883 .peek = qdisc_peek_dequeued,
886 .destroy = fq_destroy,
889 .dump_stats = fq_dump_stats,
890 .owner = THIS_MODULE,
893 static int __init fq_module_init(void)
897 fq_flow_cachep = kmem_cache_create("fq_flow_cache",
898 sizeof(struct fq_flow),
903 ret = register_qdisc(&fq_qdisc_ops);
905 kmem_cache_destroy(fq_flow_cachep);
909 static void __exit fq_module_exit(void)
911 unregister_qdisc(&fq_qdisc_ops);
912 kmem_cache_destroy(fq_flow_cachep);
915 module_init(fq_module_init)
916 module_exit(fq_module_exit)
917 MODULE_AUTHOR("Eric Dumazet");
918 MODULE_LICENSE("GPL");