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 */
  81static atomic_t         rds_cong_generation = ATOMIC_INIT(0);
  82
  83/*
  84 * Congestion monitoring
  85 */
  86static LIST_HEAD(rds_cong_monitor);
  87static 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 */
 101static DEFINE_SPINLOCK(rds_cong_lock);
 102static struct rb_root rds_cong_tree = RB_ROOT;
 103
 104static 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 */
 135static 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
 167out:
 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 */
 183void 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
 193void 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
 203int 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
 214void 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
 231void 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}
 258EXPORT_SYMBOL_GPL(rds_cong_map_updated);
 259
 260int 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 */
 277void 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
 291void 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
 305static 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
 316void 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
 326void 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
 346int 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
 377void 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 */
 396struct 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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