RDS: Congestion-handling code
RDS handles per-socket congestion by updating peers with a complete
congestion map (8KB). This code keeps track of these maps for itself
and ones received from peers.
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rds/cong.c b/net/rds/cong.c
new file mode 100644
index 0000000..90e6b31
--- /dev/null
+++ b/net/rds/cong.c
@@ -0,0 +1,402 @@
+/*
+ * Copyright (c) 2007 Oracle. All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses. You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following
+ * disclaimer in the documentation and/or other materials
+ * provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/types.h>
+#include <linux/rbtree.h>
+
+#include "rds.h"
+
+/*
+ * This file implements the receive side of the unconventional congestion
+ * management in RDS.
+ *
+ * Messages waiting in the receive queue on the receiving socket are accounted
+ * against the sockets SO_RCVBUF option value. Only the payload bytes in the
+ * message are accounted for. If the number of bytes queued equals or exceeds
+ * rcvbuf then the socket is congested. All sends attempted to this socket's
+ * address should return block or return -EWOULDBLOCK.
+ *
+ * Applications are expected to be reasonably tuned such that this situation
+ * very rarely occurs. An application encountering this "back-pressure" is
+ * considered a bug.
+ *
+ * This is implemented by having each node maintain bitmaps which indicate
+ * which ports on bound addresses are congested. As the bitmap changes it is
+ * sent through all the connections which terminate in the local address of the
+ * bitmap which changed.
+ *
+ * The bitmaps are allocated as connections are brought up. This avoids
+ * allocation in the interrupt handling path which queues messages on sockets.
+ * The dense bitmaps let transports send the entire bitmap on any bitmap change
+ * reasonably efficiently. This is much easier to implement than some
+ * finer-grained communication of per-port congestion. The sender does a very
+ * inexpensive bit test to test if the port it's about to send to is congested
+ * or not.
+ */
+
+/*
+ * Interaction with poll is a tad tricky. We want all processes stuck in
+ * poll to wake up and check whether a congested destination became uncongested.
+ * The really sad thing is we have no idea which destinations the application
+ * wants to send to - we don't even know which rds_connections are involved.
+ * So until we implement a more flexible rds poll interface, we have to make
+ * do with this:
+ * We maintain a global counter that is incremented each time a congestion map
+ * update is received. Each rds socket tracks this value, and if rds_poll
+ * finds that the saved generation number is smaller than the global generation
+ * number, it wakes up the process.
+ */
+static atomic_t rds_cong_generation = ATOMIC_INIT(0);
+
+/*
+ * Congestion monitoring
+ */
+static LIST_HEAD(rds_cong_monitor);
+static DEFINE_RWLOCK(rds_cong_monitor_lock);
+
+/*
+ * Yes, a global lock. It's used so infrequently that it's worth keeping it
+ * global to simplify the locking. It's only used in the following
+ * circumstances:
+ *
+ * - on connection buildup to associate a conn with its maps
+ * - on map changes to inform conns of a new map to send
+ *
+ * It's sadly ordered under the socket callback lock and the connection lock.
+ * Receive paths can mark ports congested from interrupt context so the
+ * lock masks interrupts.
+ */
+static DEFINE_SPINLOCK(rds_cong_lock);
+static struct rb_root rds_cong_tree = RB_ROOT;
+
+static struct rds_cong_map *rds_cong_tree_walk(__be32 addr,
+ struct rds_cong_map *insert)
+{
+ struct rb_node **p = &rds_cong_tree.rb_node;
+ struct rb_node *parent = NULL;
+ struct rds_cong_map *map;
+
+ while (*p) {
+ parent = *p;
+ map = rb_entry(parent, struct rds_cong_map, m_rb_node);
+
+ if (addr < map->m_addr)
+ p = &(*p)->rb_left;
+ else if (addr > map->m_addr)
+ p = &(*p)->rb_right;
+ else
+ return map;
+ }
+
+ if (insert) {
+ rb_link_node(&insert->m_rb_node, parent, p);
+ rb_insert_color(&insert->m_rb_node, &rds_cong_tree);
+ }
+ return NULL;
+}
+
+/*
+ * There is only ever one bitmap for any address. Connections try and allocate
+ * these bitmaps in the process getting pointers to them. The bitmaps are only
+ * ever freed as the module is removed after all connections have been freed.
+ */
+static struct rds_cong_map *rds_cong_from_addr(__be32 addr)
+{
+ struct rds_cong_map *map;
+ struct rds_cong_map *ret = NULL;
+ unsigned long zp;
+ unsigned long i;
+ unsigned long flags;
+
+ map = kzalloc(sizeof(struct rds_cong_map), GFP_KERNEL);
+ if (map == NULL)
+ return NULL;
+
+ map->m_addr = addr;
+ init_waitqueue_head(&map->m_waitq);
+ INIT_LIST_HEAD(&map->m_conn_list);
+
+ for (i = 0; i < RDS_CONG_MAP_PAGES; i++) {
+ zp = get_zeroed_page(GFP_KERNEL);
+ if (zp == 0)
+ goto out;
+ map->m_page_addrs[i] = zp;
+ }
+
+ spin_lock_irqsave(&rds_cong_lock, flags);
+ ret = rds_cong_tree_walk(addr, map);
+ spin_unlock_irqrestore(&rds_cong_lock, flags);
+
+ if (ret == NULL) {
+ ret = map;
+ map = NULL;
+ }
+
+out:
+ if (map) {
+ for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
+ free_page(map->m_page_addrs[i]);
+ kfree(map);
+ }
+
+ rdsdebug("map %p for addr %x\n", ret, be32_to_cpu(addr));
+
+ return ret;
+}
+
+/*
+ * Put the conn on its local map's list. This is called when the conn is
+ * really added to the hash. It's nested under the rds_conn_lock, sadly.
+ */
+void rds_cong_add_conn(struct rds_connection *conn)
+{
+ unsigned long flags;
+
+ rdsdebug("conn %p now on map %p\n", conn, conn->c_lcong);
+ spin_lock_irqsave(&rds_cong_lock, flags);
+ list_add_tail(&conn->c_map_item, &conn->c_lcong->m_conn_list);
+ spin_unlock_irqrestore(&rds_cong_lock, flags);
+}
+
+void rds_cong_remove_conn(struct rds_connection *conn)
+{
+ unsigned long flags;
+
+ rdsdebug("removing conn %p from map %p\n", conn, conn->c_lcong);
+ spin_lock_irqsave(&rds_cong_lock, flags);
+ list_del_init(&conn->c_map_item);
+ spin_unlock_irqrestore(&rds_cong_lock, flags);
+}
+
+int rds_cong_get_maps(struct rds_connection *conn)
+{
+ conn->c_lcong = rds_cong_from_addr(conn->c_laddr);
+ conn->c_fcong = rds_cong_from_addr(conn->c_faddr);
+
+ if (conn->c_lcong == NULL || conn->c_fcong == NULL)
+ return -ENOMEM;
+
+ return 0;
+}
+
+void rds_cong_queue_updates(struct rds_cong_map *map)
+{
+ struct rds_connection *conn;
+ unsigned long flags;
+
+ spin_lock_irqsave(&rds_cong_lock, flags);
+
+ list_for_each_entry(conn, &map->m_conn_list, c_map_item) {
+ if (!test_and_set_bit(0, &conn->c_map_queued)) {
+ rds_stats_inc(s_cong_update_queued);
+ queue_delayed_work(rds_wq, &conn->c_send_w, 0);
+ }
+ }
+
+ spin_unlock_irqrestore(&rds_cong_lock, flags);
+}
+
+void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask)
+{
+ rdsdebug("waking map %p for %pI4\n",
+ map, &map->m_addr);
+ rds_stats_inc(s_cong_update_received);
+ atomic_inc(&rds_cong_generation);
+ if (waitqueue_active(&map->m_waitq))
+ wake_up(&map->m_waitq);
+ if (waitqueue_active(&rds_poll_waitq))
+ wake_up_all(&rds_poll_waitq);
+
+ if (portmask && !list_empty(&rds_cong_monitor)) {
+ unsigned long flags;
+ struct rds_sock *rs;
+
+ read_lock_irqsave(&rds_cong_monitor_lock, flags);
+ list_for_each_entry(rs, &rds_cong_monitor, rs_cong_list) {
+ spin_lock(&rs->rs_lock);
+ rs->rs_cong_notify |= (rs->rs_cong_mask & portmask);
+ rs->rs_cong_mask &= ~portmask;
+ spin_unlock(&rs->rs_lock);
+ if (rs->rs_cong_notify)
+ rds_wake_sk_sleep(rs);
+ }
+ read_unlock_irqrestore(&rds_cong_monitor_lock, flags);
+ }
+}
+
+int rds_cong_updated_since(unsigned long *recent)
+{
+ unsigned long gen = atomic_read(&rds_cong_generation);
+
+ if (likely(*recent == gen))
+ return 0;
+ *recent = gen;
+ return 1;
+}
+
+/*
+ * We're called under the locking that protects the sockets receive buffer
+ * consumption. This makes it a lot easier for the caller to only call us
+ * when it knows that an existing set bit needs to be cleared, and vice versa.
+ * We can't block and we need to deal with concurrent sockets working against
+ * the same per-address map.
+ */
+void rds_cong_set_bit(struct rds_cong_map *map, __be16 port)
+{
+ unsigned long i;
+ unsigned long off;
+
+ rdsdebug("setting congestion for %pI4:%u in map %p\n",
+ &map->m_addr, ntohs(port), map);
+
+ i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
+ off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
+
+ generic___set_le_bit(off, (void *)map->m_page_addrs[i]);
+}
+
+void rds_cong_clear_bit(struct rds_cong_map *map, __be16 port)
+{
+ unsigned long i;
+ unsigned long off;
+
+ rdsdebug("clearing congestion for %pI4:%u in map %p\n",
+ &map->m_addr, ntohs(port), map);
+
+ i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
+ off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
+
+ generic___clear_le_bit(off, (void *)map->m_page_addrs[i]);
+}
+
+static int rds_cong_test_bit(struct rds_cong_map *map, __be16 port)
+{
+ unsigned long i;
+ unsigned long off;
+
+ i = be16_to_cpu(port) / RDS_CONG_MAP_PAGE_BITS;
+ off = be16_to_cpu(port) % RDS_CONG_MAP_PAGE_BITS;
+
+ return generic_test_le_bit(off, (void *)map->m_page_addrs[i]);
+}
+
+void rds_cong_add_socket(struct rds_sock *rs)
+{
+ unsigned long flags;
+
+ write_lock_irqsave(&rds_cong_monitor_lock, flags);
+ if (list_empty(&rs->rs_cong_list))
+ list_add(&rs->rs_cong_list, &rds_cong_monitor);
+ write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
+}
+
+void rds_cong_remove_socket(struct rds_sock *rs)
+{
+ unsigned long flags;
+ struct rds_cong_map *map;
+
+ write_lock_irqsave(&rds_cong_monitor_lock, flags);
+ list_del_init(&rs->rs_cong_list);
+ write_unlock_irqrestore(&rds_cong_monitor_lock, flags);
+
+ /* update congestion map for now-closed port */
+ spin_lock_irqsave(&rds_cong_lock, flags);
+ map = rds_cong_tree_walk(rs->rs_bound_addr, NULL);
+ spin_unlock_irqrestore(&rds_cong_lock, flags);
+
+ if (map && rds_cong_test_bit(map, rs->rs_bound_port)) {
+ rds_cong_clear_bit(map, rs->rs_bound_port);
+ rds_cong_queue_updates(map);
+ }
+}
+
+int rds_cong_wait(struct rds_cong_map *map, __be16 port, int nonblock,
+ struct rds_sock *rs)
+{
+ if (!rds_cong_test_bit(map, port))
+ return 0;
+ if (nonblock) {
+ if (rs && rs->rs_cong_monitor) {
+ unsigned long flags;
+
+ /* It would have been nice to have an atomic set_bit on
+ * a uint64_t. */
+ spin_lock_irqsave(&rs->rs_lock, flags);
+ rs->rs_cong_mask |= RDS_CONG_MONITOR_MASK(ntohs(port));
+ spin_unlock_irqrestore(&rs->rs_lock, flags);
+
+ /* Test again - a congestion update may have arrived in
+ * the meantime. */
+ if (!rds_cong_test_bit(map, port))
+ return 0;
+ }
+ rds_stats_inc(s_cong_send_error);
+ return -ENOBUFS;
+ }
+
+ rds_stats_inc(s_cong_send_blocked);
+ rdsdebug("waiting on map %p for port %u\n", map, be16_to_cpu(port));
+
+ return wait_event_interruptible(map->m_waitq,
+ !rds_cong_test_bit(map, port));
+}
+
+void rds_cong_exit(void)
+{
+ struct rb_node *node;
+ struct rds_cong_map *map;
+ unsigned long i;
+
+ while ((node = rb_first(&rds_cong_tree))) {
+ map = rb_entry(node, struct rds_cong_map, m_rb_node);
+ rdsdebug("freeing map %p\n", map);
+ rb_erase(&map->m_rb_node, &rds_cong_tree);
+ for (i = 0; i < RDS_CONG_MAP_PAGES && map->m_page_addrs[i]; i++)
+ free_page(map->m_page_addrs[i]);
+ kfree(map);
+ }
+}
+
+/*
+ * Allocate a RDS message containing a congestion update.
+ */
+struct rds_message *rds_cong_update_alloc(struct rds_connection *conn)
+{
+ struct rds_cong_map *map = conn->c_lcong;
+ struct rds_message *rm;
+
+ rm = rds_message_map_pages(map->m_page_addrs, RDS_CONG_MAP_BYTES);
+ if (!IS_ERR(rm))
+ rm->m_inc.i_hdr.h_flags = RDS_FLAG_CONG_BITMAP;
+
+ return rm;
+}