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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                         rds_send_xmit(conn);
225                 }
226         }
227 
228         spin_unlock_irqrestore(&rds_cong_lock, flags);
229 }
230 
231 void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask)
232 {
233         rdsdebug("waking map %p for %pI4\n",
234           map, &map->m_addr);
235         rds_stats_inc(s_cong_update_received);
236         atomic_inc(&rds_cong_generation);
237         if (waitqueue_active(&map->m_waitq))
238                 wake_up(&map->m_waitq);
239         if (waitqueue_active(&rds_poll_waitq))
240                 wake_up_all(&rds_poll_waitq);
241 
242         if (portmask && !list_empty(&rds_cong_monitor)) {
243                 unsigned long flags;
244                 struct rds_sock *rs;
245 
246                 read_lock_irqsave(&rds_cong_monitor_lock, flags);
247                 list_for_each_entry(rs, &rds_cong_monitor, rs_cong_list) {
248                         spin_lock(&rs->rs_lock);
249                         rs->rs_cong_notify |= (rs->rs_cong_mask & portmask);
250                         rs->rs_cong_mask &= ~portmask;
251                         spin_unlock(&rs->rs_lock);
252                         if (rs->rs_cong_notify)
253                                 rds_wake_sk_sleep(rs);
254                 }
255                 read_unlock_irqrestore(&rds_cong_monitor_lock, flags);
256         }
257 }
258 EXPORT_SYMBOL_GPL(rds_cong_map_updated);
259 
260 int rds_cong_updated_since(unsigned long *recent)
261 {
262         unsigned long gen = atomic_read(&rds_cong_generation);
263 
264         if (likely(*recent == gen))
265                 return 0;
266         *recent = gen;
267         return 1;
268 }
269 
270 /*
271  * We're called under the locking that protects the sockets receive buffer
272  * consumption.  This makes it a lot easier for the caller to only call us
273  * when it knows that an existing set bit needs to be cleared, and vice versa.
274  * We can't block and we need to deal with concurrent sockets working against
275  * the same per-address map.
276  */
277 void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
278 {
279         unsigned long i;
280         unsigned long off;
281 
282         rdsdebug("setting congestion for %pI4:%u in map %p\n",
283           &map->m_addr, ntohs(port), map);
284 
285         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
286         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
287 
288         __set_bit_le(off, (void *)map->m_page_addrs[i]);
289 }
290 
291 void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
292 {
293         unsigned long i;
294         unsigned long off;
295 
296         rdsdebug("clearing 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         __clear_bit_le(off, (void *)map->m_page_addrs[i]);
303 }
304 
305 static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)
306 {
307         unsigned long i;
308         unsigned long off;
309 
310         i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
311         off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
312 
313         return test_bit_le(off, (void *)map->m_page_addrs[i]);
314 }
315 
316 void rds_cong_add_socket(struct rds_sock *rs)
317 {
318         unsigned long flags;
319 
320         write_lock_irqsave(&rds_cong_monitor_lock, flags);
321         if (list_empty(&rs->rs_cong_list))
322                 list_add(&rs->rs_cong_list, &rds_cong_monitor);
323         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
324 }
325 
326 void rds_cong_remove_socket(struct rds_sock *rs)
327 {
328         unsigned long flags;
329         struct rds_cong_map *map;
330 
331         write_lock_irqsave(&rds_cong_monitor_lock, flags);
332         list_del_init(&rs->rs_cong_list);
333         write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
334 
335         /* update congestion map for now-closed port */
336         spin_lock_irqsave(&rds_cong_lock, flags);
337         map = rds_cong_tree_walk(rs->rs_bound_addr, NULL);
338         spin_unlock_irqrestore(&rds_cong_lock, flags);
339 
340         if (map && rds_cong_test_bit(map, rs->rs_bound_port)) {
341                 rds_cong_clear_bit(map, rs->rs_bound_port);
342                 rds_cong_queue_updates(map);
343         }
344 }
345 
346 int rds_cong_wait(struct rds_cong_map *map, __be16 port, int nonblock,
347                   struct rds_sock *rs)
348 {
349         if (!rds_cong_test_bit(map, port))
350                 return 0;
351         if (nonblock) {
352                 if (rs && rs->rs_cong_monitor) {
353                         unsigned long flags;
354 
355                         /* It would have been nice to have an atomic set_bit on
356                          * a uint64_t. */
357                         spin_lock_irqsave(&rs->rs_lock, flags);
358                         rs->rs_cong_mask |= RDS_CONG_MONITOR_MASK(ntohs(port));
359                         spin_unlock_irqrestore(&rs->rs_lock, flags);
360 
361                         /* Test again - a congestion update may have arrived in
362                          * the meantime. */
363                         if (!rds_cong_test_bit(map, port))
364                                 return 0;
365                 }
366                 rds_stats_inc(s_cong_send_error);
367                 return -ENOBUFS;
368         }
369 
370         rds_stats_inc(s_cong_send_blocked);
371         rdsdebug("waiting on map %p for port %u\n", map, be16_to_cpu(port));
372 
373         return wait_event_interruptible(map->m_waitq,
374                                         !rds_cong_test_bit(map, port));
375 }
376 
377 void rds_cong_exit(void)
378 {
379         struct rb_node *node;
380         struct rds_cong_map *map;
381         unsigned long i;
382 
383         while ((node = rb_first(&rds_cong_tree))) {
384                 map = rb_entry(node, struct rds_cong_map, m_rb_node);
385                 rdsdebug("freeing map %p\n", map);
386                 rb_erase(&map->m_rb_node, &rds_cong_tree);
387                 for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
388                         free_page(map->m_page_addrs[i]);
389                 kfree(map);
390         }
391 }
392 
393 /*
394  * Allocate a RDS message containing a congestion update.
395  */
396 struct rds_message *rds_cong_update_alloc(struct rds_connection *conn)
397 {
398         struct rds_cong_map *map = conn->c_lcong;
399         struct rds_message *rm;
400 
401         rm = rds_message_map_pages(map->m_page_addrs, RDS_CONG_MAP_BYTES);
402         if (!IS_ERR(rm))
403                 rm->m_inc.i_hdr.h_flags = RDS_FLAG_CONG_BITMAP;
404 
405         return rm;
406 }
407 

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