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TOMOYO Linux Cross Reference
Linux/net/rds/cong.c

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  1 /*
  2  * Copyright (c) 2007 Oracle.  All rights reserved.
  3  *
  4  * This software is available to you under a choice of one of two
  5  * licenses.  You may choose to be licensed under the terms of the GNU
  6  * General Public License (GPL) Version 2, available from the file
  7  * COPYING in the main directory of this source tree, or the
  8  * OpenIB.org BSD license below:
  9  *
 10  *     Redistribution and use in source and binary forms, with or
 11  *     without modification, are permitted provided that the following
 12  *     conditions are met:
 13  *
 14  *      - Redistributions of source code must retain the above
 15  *        copyright notice, this list of conditions and the following
 16  *        disclaimer.
 17  *
 18  *      - Redistributions in binary form must reproduce the above
 19  *        copyright notice, this list of conditions and the following
 20  *        disclaimer in the documentation and/or other materials
 21  *        provided with the distribution.
 22  *
 23  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 24  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 25  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 26  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 27  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 28  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 29  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 30  * SOFTWARE.
 31  *
 32  */
 33 #include <linux/slab.h>
 34 #include <linux/types.h>
 35 #include <linux/rbtree.h>
 36 #include <linux/bitops.h>
 37 #include <linux/export.h>
 38 
 39 #include "rds.h"
 40 
 41 /*
 42  * This file implements the receive side of the unconventional congestion
 43  * management in RDS.
 44  *
 45  * Messages waiting in the receive queue on the receiving socket are accounted
 46  * against the sockets SO_RCVBUF option value.  Only the payload bytes in the
 47  * message are accounted for.  If the number of bytes queued equals or exceeds
 48  * rcvbuf then the socket is congested.  All sends attempted to this socket's
 49  * address should return block or return -EWOULDBLOCK.
 50  *
 51  * Applications are expected to be reasonably tuned such that this situation
 52  * very rarely occurs.  An application encountering this "back-pressure" is
 53  * considered a bug.
 54  *
 55  * This is implemented by having each node maintain bitmaps which indicate
 56  * which ports on bound addresses are congested.  As the bitmap changes it is
 57  * sent through all the connections which terminate in the local address of the
 58  * bitmap which changed.
 59  *
 60  * The bitmaps are allocated as connections are brought up.  This avoids
 61  * allocation in the interrupt handling path which queues messages on sockets.
 62  * The dense bitmaps let transports send the entire bitmap on any bitmap change
 63  * reasonably efficiently.  This is much easier to implement than some
 64  * finer-grained communication of per-port congestion.  The sender does a very
 65  * inexpensive bit test to test if the port it's about to send to is congested
 66  * or not.
 67  */
 68 
 69 /*
 70  * Interaction with poll is a tad tricky. We want all processes stuck in
 71  * poll to wake up and check whether a congested destination became uncongested.
 72  * The really sad thing is we have no idea which destinations the application
 73  * wants to send to - we don't even know which rds_connections are involved.
 74  * So until we implement a more flexible rds poll interface, we have to make
 75  * do with this:
 76  * We maintain a global counter that is incremented each time a congestion map
 77  * update is received. Each rds socket tracks this value, and if rds_poll
 78  * finds that the saved generation number is smaller than the global generation
 79  * number, it wakes up the process.
 80  */
 81 static atomic_t         rds_cong_generation = ATOMIC_INIT(0);
 82 
 83 /*
 84  * Congestion monitoring
 85  */
 86 static LIST_HEAD(rds_cong_monitor);
 87 static DEFINE_RWLOCK(rds_cong_monitor_lock);
 88 
 89 /*
 90  * Yes, a global lock.  It's used so infrequently that it's worth keeping it
 91  * global to simplify the locking.  It's only used in the following
 92  * circumstances:
 93  *
 94  *  - on connection buildup to associate a conn with its maps
 95  *  - on map changes to inform conns of a new map to send
 96  *
 97  *  It's sadly ordered under the socket callback lock and the connection lock.
 98  *  Receive paths can mark ports congested from interrupt context so the
 99  *  lock masks interrupts.
100  */
101 static DEFINE_SPINLOCK(rds_cong_lock);
102 static struct rb_root rds_cong_tree = RB_ROOT;
103 
104 static struct rds_cong_map *rds_cong_tree_walk(__be32 addr,
105                                                struct rds_cong_map *insert)
106 {
107         struct rb_node **p = &rds_cong_tree.rb_node;
108         struct rb_node *parent = NULL;
109         struct rds_cong_map *map;
110 
111         while (*p) {
112                 parent = *p;
113                 map = rb_entry(parent, struct rds_cong_map, m_rb_node);
114 
115                 if (addr < map->m_addr)
116                         p = &(*p)->rb_left;
117                 else if (addr > map->m_addr)
118                         p = &(*p)->rb_right;
119                 else
120                         return map;
121         }
122 
123         if (insert) {
124                 rb_link_node(&insert->m_rb_node, parent, p);
125                 rb_insert_color(&insert->m_rb_node, &rds_cong_tree);
126         }
127         return NULL;
128 }
129 
130 /*
131  * There is only ever one bitmap for any address.  Connections try and allocate
132  * these bitmaps in the process getting pointers to them.  The bitmaps are only
133  * ever freed as the module is removed after all connections have been freed.
134  */
135 static struct rds_cong_map *rds_cong_from_addr(__be32 addr)
136 {
137         struct rds_cong_map *map;
138         struct rds_cong_map *ret = NULL;
139         unsigned long zp;
140         unsigned long i;
141         unsigned long flags;
142 
143         map = kzalloc(sizeof(struct rds_cong_map), GFP_KERNEL);
144         if (!map)
145                 return NULL;
146 
147         map->m_addr = addr;
148         init_waitqueue_head(&map->m_waitq);
149         INIT_LIST_HEAD(&map->m_conn_list);
150 
151         for (i = 0; i < RDS_CONG_MAP_PAGES; i++) {
152                 zp = get_zeroed_page(GFP_KERNEL);
153                 if (zp == 0)
154                         goto out;
155                 map->m_page_addrs[i] = zp;
156         }
157 
158         spin_lock_irqsave(&rds_cong_lock, flags);
159         ret = rds_cong_tree_walk(addr, map);
160         spin_unlock_irqrestore(&rds_cong_lock, flags);
161 
162         if (!ret) {
163                 ret = map;
164                 map = NULL;
165         }
166 
167 out:
168         if (map) {
169                 for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
170                         free_page(map->m_page_addrs[i]);
171                 kfree(map);
172         }
173 
174         rdsdebug("map %p for addr %x\n", ret, be32_to_cpu(addr));
175 
176         return ret;
177 }
178 
179 /*
180  * Put the conn on its local map's list.  This is called when the conn is
181  * really added to the hash.  It's nested under the rds_conn_lock, sadly.
182  */
183 void rds_cong_add_conn(struct rds_connection *conn)
184 {
185         unsigned long flags;
186 
187         rdsdebug("conn %p now on map %p\n", conn, conn->c_lcong);
188         spin_lock_irqsave(&rds_cong_lock, flags);
189         list_add_tail(&conn->c_map_item, &conn->c_lcong->m_conn_list);
190         spin_unlock_irqrestore(&rds_cong_lock, flags);
191 }
192 
193 void rds_cong_remove_conn(struct rds_connection *conn)
194 {
195         unsigned long flags;
196 
197         rdsdebug("removing conn %p from map %p\n", conn, conn->c_lcong);
198         spin_lock_irqsave(&rds_cong_lock, flags);
199         list_del_init(&conn->c_map_item);
200         spin_unlock_irqrestore(&rds_cong_lock, flags);
201 }
202 
203 int rds_cong_get_maps(struct rds_connection *conn)
204 {
205         conn->c_lcong = rds_cong_from_addr(conn->c_laddr);
206         conn->c_fcong = rds_cong_from_addr(conn->c_faddr);
207 
208         if (!(conn->c_lcong && conn->c_fcong))
209                 return -ENOMEM;
210 
211         return 0;
212 }
213 
214 void rds_cong_queue_updates(struct rds_cong_map *map)
215 {
216         struct rds_connection *conn;
217         unsigned long flags;
218 
219         spin_lock_irqsave(&rds_cong_lock, flags);
220 
221         list_for_each_entry(conn, &map->m_conn_list, c_map_item) {
222                 if (!test_and_set_bit(0, &conn->c_map_queued)) {
223                         rds_stats_inc(s_cong_update_queued);
224                         /* We cannot inline the call to rds_send_xmit() here
225                          * for two reasons (both pertaining to a TCP transport):
226                          * 1. When we get here from the receive path, we
227                          *    are already holding the sock_lock (held by
228                          *    tcp_v4_rcv()). So inlining calls to
229                          *    tcp_setsockopt and/or tcp_sendmsg will deadlock
230                          *    when it tries to get the sock_lock())
231                          * 2. Interrupts are masked so that we can mark the
232                          *    the port congested from both send and recv paths.
233                          *    (See comment around declaration of rdc_cong_lock).
234                          *    An attempt to get the sock_lock() here will
235                          *    therefore trigger warnings.
236                          * Defer the xmit to rds_send_worker() instead.
237                          */
238                         queue_delayed_work(rds_wq, &conn->c_send_w, 0);
239                 }
240         }
241 
242         spin_unlock_irqrestore(&rds_cong_lock, flags);
243 }
244 
245 void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask)
246 {
247         rdsdebug("waking map %p for %pI4\n",
248           map, &map->m_addr);
249         rds_stats_inc(s_cong_update_received);
250         atomic_inc(&rds_cong_generation);
251         if (waitqueue_active(&map->m_waitq))
252                 wake_up(&map->m_waitq);
253         if (waitqueue_active(&rds_poll_waitq))
254                 wake_up_all(&rds_poll_waitq);
255 
256         if (portmask && !list_empty(&rds_cong_monitor)) {
257                 unsigned long flags;
258                 struct rds_sock *rs;
259 
260                 read_lock_irqsave(&rds_cong_monitor_lock, flags);
261                 list_for_each_entry(rs, &rds_cong_monitor, rs_cong_list) {
262                         spin_lock(&rs->rs_lock);
263                         rs->rs_cong_notify |= (rs->rs_cong_mask & portmask);
264                         rs->rs_cong_mask &= ~portmask;
265                         spin_unlock(&rs->rs_lock);
266                         if (rs->rs_cong_notify)
267                                 rds_wake_sk_sleep(rs);
268                 }
269                 read_unlock_irqrestore(&rds_cong_monitor_lock, flags);
270         }
271 }
272 EXPORT_SYMBOL_GPL(rds_cong_map_updated);
273 
274 int rds_cong_updated_since(unsigned long *recent)
275 {
276         unsigned long gen = atomic_read(&rds_cong_generation);
277 
278         if (likely(*recent == gen))
279                 return 0;
280         *recent = gen;
281         return 1;
282 }
283 
284 /*
285  * We're called under the locking that protects the sockets receive buffer
286  * consumption.  This makes it a lot easier for the caller to only call us
287  * when it knows that an existing set bit needs to be cleared, and vice versa.
288  * We can't block and we need to deal with concurrent sockets working against
289  * the same per-address map.
290  */
291 void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
292 {
293         unsigned long i;
294         unsigned long off;
295 
296         rdsdebug("setting congestion for %pI4:%u in map %p\n",
297           &map->m_addr, ntohs(port), map);
298 
299         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
300         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
301 
302         set_bit_le(off, (void *)map->m_page_addrs[i]);
303 }
304 
305 void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
306 {
307         unsigned long i;
308         unsigned long off;
309 
310         rdsdebug("clearing congestion for %pI4:%u in map %p\n",
311           &map->m_addr, ntohs(port), map);
312 
313         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
314         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
315 
316         clear_bit_le(off, (void *)map->m_page_addrs[i]);
317 }
318 
319 static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)
320 {
321         unsigned long i;
322         unsigned long off;
323 
324         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
325         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
326 
327         return test_bit_le(off, (void *)map->m_page_addrs[i]);
328 }
329 
330 void rds_cong_add_socket(struct rds_sock *rs)
331 {
332         unsigned long flags;
333 
334         write_lock_irqsave(&rds_cong_monitor_lock, flags);
335         if (list_empty(&rs->rs_cong_list))
336                 list_add(&rs->rs_cong_list, &rds_cong_monitor);
337         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
338 }
339 
340 void rds_cong_remove_socket(struct rds_sock *rs)
341 {
342         unsigned long flags;
343         struct rds_cong_map *map;
344 
345         write_lock_irqsave(&rds_cong_monitor_lock, flags);
346         list_del_init(&rs->rs_cong_list);
347         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
348 
349         /* update congestion map for now-closed port */
350         spin_lock_irqsave(&rds_cong_lock, flags);
351         map = rds_cong_tree_walk(rs->rs_bound_addr, NULL);
352         spin_unlock_irqrestore(&rds_cong_lock, flags);
353 
354         if (map && rds_cong_test_bit(map, rs->rs_bound_port)) {
355                 rds_cong_clear_bit(map, rs->rs_bound_port);
356                 rds_cong_queue_updates(map);
357         }
358 }
359 
360 int rds_cong_wait(struct rds_cong_map *map, __be16 port, int nonblock,
361                   struct rds_sock *rs)
362 {
363         if (!rds_cong_test_bit(map, port))
364                 return 0;
365         if (nonblock) {
366                 if (rs && rs->rs_cong_monitor) {
367                         unsigned long flags;
368 
369                         /* It would have been nice to have an atomic set_bit on
370                          * a uint64_t. */
371                         spin_lock_irqsave(&rs->rs_lock, flags);
372                         rs->rs_cong_mask |= RDS_CONG_MONITOR_MASK(ntohs(port));
373                         spin_unlock_irqrestore(&rs->rs_lock, flags);
374 
375                         /* Test again - a congestion update may have arrived in
376                          * the meantime. */
377                         if (!rds_cong_test_bit(map, port))
378                                 return 0;
379                 }
380                 rds_stats_inc(s_cong_send_error);
381                 return -ENOBUFS;
382         }
383 
384         rds_stats_inc(s_cong_send_blocked);
385         rdsdebug("waiting on map %p for port %u\n", map, be16_to_cpu(port));
386 
387         return wait_event_interruptible(map->m_waitq,
388                                         !rds_cong_test_bit(map, port));
389 }
390 
391 void rds_cong_exit(void)
392 {
393         struct rb_node *node;
394         struct rds_cong_map *map;
395         unsigned long i;
396 
397         while ((node = rb_first(&rds_cong_tree))) {
398                 map = rb_entry(node, struct rds_cong_map, m_rb_node);
399                 rdsdebug("freeing map %p\n", map);
400                 rb_erase(&map->m_rb_node, &rds_cong_tree);
401                 for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
402                         free_page(map->m_page_addrs[i]);
403                 kfree(map);
404         }
405 }
406 
407 /*
408  * Allocate a RDS message containing a congestion update.
409  */
410 struct rds_message *rds_cong_update_alloc(struct rds_connection *conn)
411 {
412         struct rds_cong_map *map = conn->c_lcong;
413         struct rds_message *rm;
414 
415         rm = rds_message_map_pages(map->m_page_addrs, RDS_CONG_MAP_BYTES);
416         if (!IS_ERR(rm))
417                 rm->m_inc.i_hdr.h_flags = RDS_FLAG_CONG_BITMAP;
418 
419         return rm;
420 }
421 

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