RDS: Congestion-handling code

/*

 * 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;

}