net/core/request_sock.c

   1 /*
   2  * NET          Generic infrastructure for Network protocols.
   3  *
   4  * Authors:     Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   5  *
   6  *              From code originally in include/net/tcp.h
   7  *
   8  *              This program is free software; you can redistribute it and/or
   9  *              modify it under the terms of the GNU General Public License
  10  *              as published by the Free Software Foundation; either version
  11  *              2 of the License, or (at your option) any later version.
  12  */
  13
  14 #include <linux/module.h>
  15 #include <linux/random.h>
  16 #include <linux/slab.h>
  17 #include <linux/string.h>
  18
  19 #include <net/request_sock.h>
  20
  21 /*
  22  * Maximum number of SYN_RECV sockets in queue per LISTEN socket.
  23  * One SYN_RECV socket costs about 80bytes on a 32bit machine.
  24  * It would be better to replace it with a global counter for all sockets
  25  * but then some measure against one socket starving all other sockets
  26  * would be needed.
  27  *
  28  * It was 128 by default. Experiments with real servers show, that
  29  * it is absolutely not enough even at 100conn/sec. 256 cures most
  30  * of problems. This value is adjusted to 128 for very small machines
  31  * (<=32Mb of memory) and to 1024 on normal or better ones (>=256Mb).
  32  * Further increasing requires to change hash table size.
  33  */
  34 int sysctl_max_syn_backlog = 256;
  35 EXPORT_SYMBOL(sysctl_max_syn_backlog);
  36
  37 int reqsk_queue_alloc(struct request_sock_queue *queue,
  38                       const int nr_table_entries)
  39 {
  40         const int lopt_size = sizeof(struct listen_sock) +
  41                               nr_table_entries * sizeof(struct request_sock *);
  42         struct listen_sock *lopt = kmalloc(lopt_size, GFP_KERNEL);
  43
  44         if (lopt == NULL)
  45                 return -ENOMEM;
  46
  47         memset(lopt, 0, lopt_size);
  48
  49         for (lopt->max_qlen_log = 6;
  50              (1 << lopt->max_qlen_log) < sysctl_max_syn_backlog;
  51              lopt->max_qlen_log++);
  52
  53         get_random_bytes(&lopt->hash_rnd, sizeof(lopt->hash_rnd));
  54         rwlock_init(&queue->syn_wait_lock);
  55         queue->rskq_accept_head = queue->rskq_accept_head = NULL;
  56
  57         write_lock_bh(&queue->syn_wait_lock);
  58         queue->listen_opt = lopt;
  59         write_unlock_bh(&queue->syn_wait_lock);
  60
  61         return 0;
  62 }
  63
  64 EXPORT_SYMBOL(reqsk_queue_alloc);