Message-ID: <485E4F71.2060607@gmail.com>
Date:	Sun, 22 Jun 2008 15:11:13 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Carl Henrik Lunde <chlunde@...g.uio.no>
CC:	balbir@...ux.vnet.ibm.com, menage@...gle.com, matt@...ehost.com,
	roberto@...it.it, randy.dunlap@...cle.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	Subrata Modak <tosubrata@...il.com>, axboe@...nel.dk,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: [PATCH 2/3] i/o bandwidth controller infrastructure

Carl Henrik Lunde wrote:
> Did you consider using token bucket instead of this (leaky bucket?)?
> 
> I've attached a patch which implements token bucket.  Although not as
> precise as the leaky bucket the performance is better at high bandwidth
> streaming loads.
> 
> The leaky bucket stops at around 53 MB/s while token bucket works for
> up to 64 MB/s.  The baseline (no cgroups) is 66 MB/s.
> 
> benchmark:
> two streaming readers (fio) with block size 128k, bucket size 4 MB
> 90% of the bandwidth was allocated to one process, the other gets 10%
> 
> bw-limit: actual bw  algorithm     bw1  bw2
>  5 MiB/s:  5.0 MiB/s leaky_bucket  0.5  4.5
>  5 MiB/s:  5.2 MiB/s token_bucket  0.6  4.6
> 10 MiB/s: 10.0 MiB/s leaky_bucket  1.0  9.0
> 10 MiB/s: 10.3 MiB/s token_bucket  1.0  9.2
> 15 MiB/s: 15.0 MiB/s leaky_bucket  1.5 13.5
> 15 MiB/s: 15.4 MiB/s token_bucket  1.5 13.8
> 20 MiB/s: 19.9 MiB/s leaky_bucket  2.0 17.9
> 20 MiB/s: 20.5 MiB/s token_bucket  2.1 18.4
> 25 MiB/s: 24.4 MiB/s leaky_bucket  2.5 21.9
> 25 MiB/s: 25.6 MiB/s token_bucket  2.6 23.0
> 30 MiB/s: 29.2 MiB/s leaky_bucket  3.0 26.2
> 30 MiB/s: 30.7 MiB/s token_bucket  3.1 27.7
> 35 MiB/s: 34.3 MiB/s leaky_bucket  3.4 30.9
> 35 MiB/s: 35.9 MiB/s token_bucket  3.6 32.3
> 40 MiB/s: 39.7 MiB/s leaky_bucket  3.9 35.8
> 40 MiB/s: 41.0 MiB/s token_bucket  4.1 36.9
> 45 MiB/s: 44.0 MiB/s leaky_bucket  4.3 39.7
> 45 MiB/s: 46.1 MiB/s token_bucket  4.6 41.5
> 50 MiB/s: 47.9 MiB/s leaky_bucket  4.7 43.2
> 50 MiB/s: 51.0 MiB/s token_bucket  5.1 45.9
> 55 MiB/s: 50.5 MiB/s leaky_bucket  5.0 45.5
> 55 MiB/s: 56.2 MiB/s token_bucket  5.6 50.5
> 60 MiB/s: 52.9 MiB/s leaky_bucket  5.2 47.7
> 60 MiB/s: 61.0 MiB/s token_bucket  6.1 54.9
> 65 MiB/s: 53.0 MiB/s leaky_bucket  5.4 47.6
> 65 MiB/s: 63.7 MiB/s token_bucket  6.6 57.1
> 70 MiB/s: 53.8 MiB/s leaky_bucket  5.5 48.4
> 70 MiB/s: 64.1 MiB/s token_bucket  7.1 57.0

Carl,

based on your token bucket solution I've implemented a run-time leaky
bucket / token bucket switcher:

# leaky bucket #
echo 0 > /cgroups/foo/blockio.throttling_strategy
# token bucket #
echo 1 > /cgroups/foo/blockio.throttling_strategy

The -rc of the new io-throttle patch 2/3 is below, 1/3 and 3/3 are the
same as patchset version 3, even if documentation must be updated. It
would be great if you could review the patch, in particular the
token_bucket() implementation and repeat your tests.

The all-in-one patch is available here:
http://download.systemimager.org/~arighi/linux/patches/io-throttle/cgroup-io-throttle-v4-rc1.patch

I also did some quick tests similar to yours, the benchmark I've used is
available here as well:
http://download.systemimager.org/~arighi/linux/patches/io-throttle/benchmark/iobw.c

= Results =
I/O scheduler: cfq
filesystem: ext3
Command: ionice -c 1 -n 0 iobw -direct 2 4m 32m
Bucket size: 4MiB

testing 2 parallel streams, chunk_size 4096KiB, data_size 32768KiB

=== no throttling ===
testing 2 parallel streams, chunk_size 4096KiB, data_size 32768KiB
[task   2] time:  2.929, bw:   10742 KiB/s (WRITE)
[task   2] time:  2.878, bw:   10742 KiB/s (READ )
[task   1] time:  2.377, bw:   13671 KiB/s (WRITE)
[task   1] time:  3.979, bw:    7812 KiB/s (READ )
[parent 0] time:  6.397, bw:   19531 KiB/s (TOTAL)

=== bandwidth limit: 4MiB/s (leaky bucket) ===
[task   2] time: 15.880, bw:    1953 KiB/s (WRITE)
[task   2] time: 14.278, bw:    1953 KiB/s (READ )
[task   1] time: 14.711, bw:    1953 KiB/s (WRITE)
[task   1] time: 16.563, bw:    1953 KiB/s (READ )
[parent 0] time: 31.316, bw:    3906 KiB/s (TOTAL)

=== bandwidth limit: 4MiB/s (token bucket) ===
[task   2] time: 11.864, bw:    1953 KiB/s (WRITE)
[task   2] time: 15.958, bw:    1953 KiB/s (READ )
[task   1] time: 19.233, bw:     976 KiB/s (WRITE)
[task   1] time: 12.643, bw:    1953 KiB/s (READ )
[parent 0] time: 31.917, bw:    3906 KiB/s (TOTAL)

=== bandwidth limit: 8MiB/s (leaky bucket) ===
[task   2] time:  7.198, bw:    3906 KiB/s (WRITE)
[task   2] time:  8.012, bw:    3906 KiB/s (READ )
[task   1] time:  7.891, bw:    3906 KiB/s (WRITE)
[task   1] time:  7.846, bw:    3906 KiB/s (READ )
[parent 0] time: 15.780, bw:    7812 KiB/s (TOTAL)

=== bandwidth limit: 8MiB/s (token bucket) ===
[task   1] time:  6.996, bw:    3906 KiB/s (WRITE)
[task   1] time:  6.529, bw:    4882 KiB/s (READ )
[task   2] time: 10.341, bw:    2929 KiB/s (WRITE)
[task   2] time:  5.681, bw:    4882 KiB/s (READ )
[parent 0] time: 16.079, bw:    7812 KiB/s (TOTAL)

=== bandwidth limit: 12MiB/s (leaky bucket) ===
[task   2] time:  4.992, bw:    5859 KiB/s (WRITE)
[task   2] time:  5.077, bw:    5859 KiB/s (READ )
[task   1] time:  5.500, bw:    5859 KiB/s (WRITE)
[task   1] time:  5.061, bw:    5859 KiB/s (READ )
[parent 0] time: 10.603, bw:   11718 KiB/s (TOTAL)

=== bandwidth limit: 12MiB/s (token bucket) ===
[task   1] time:  5.057, bw:    5859 KiB/s (WRITE)
[task   1] time:  4.329, bw:    6835 KiB/s (READ )
[task   2] time:  5.771, bw:    4882 KiB/s (WRITE)
[task   2] time:  4.961, bw:    5859 KiB/s (READ )
[parent 0] time: 10.786, bw:   11718 KiB/s (TOTAL)

=== bandwidth limit: 16MiB/s (leaky bucket) ===
[task   1] time:  3.737, bw:    7812 KiB/s (WRITE)
[task   1] time:  3.988, bw:    7812 KiB/s (READ )
[task   2] time:  4.043, bw:    7812 KiB/s (WRITE)
[task   2] time:  3.954, bw:    7812 KiB/s (READ )
[parent 0] time:  8.040, bw:   15625 KiB/s (TOTAL)

=== bandwidth limit: 16MiB/s (token bucket) ===
[task   1] time:  3.224, bw:    9765 KiB/s (WRITE)
[task   1] time:  3.550, bw:    8789 KiB/s (READ )
[task   2] time:  5.085, bw:    5859 KiB/s (WRITE)
[task   2] time:  3.033, bw:   10742 KiB/s (READ )
[parent 0] time:  8.160, bw:   15625 KiB/s (TOTAL)

=== bandwidth limit: 20MiB/s (leaky bucket) ===
[task   1] time:  3.265, bw:    9765 KiB/s (WRITE)
[task   1] time:  3.339, bw:    9765 KiB/s (READ )
[task   2] time:  3.001, bw:   10742 KiB/s (WRITE)
[task   2] time:  3.840, bw:    7812 KiB/s (READ )
[parent 0] time:  6.884, bw:   18554 KiB/s (TOTAL)

=== bandwidth limit: 20MiB/s (token bucket) ===
[task   1] time:  2.897, bw:   10742 KiB/s (WRITE)
[task   1] time:  3.071, bw:    9765 KiB/s (READ )
[task   2] time:  3.697, bw:    8789 KiB/s (WRITE)
[task   2] time:  2.925, bw:   10742 KiB/s (READ )
[parent 0] time:  6.657, bw:   19531 KiB/s (TOTAL)

=== bandwidth limit: 24MiB/s (leaky bucket) ===
[task   1] time:  2.283, bw:   13671 KiB/s (WRITE)
[task   1] time:  3.626, bw:    8789 KiB/s (READ )
[task   2] time:  3.892, bw:    7812 KiB/s (WRITE)
[task   2] time:  2.774, bw:   11718 KiB/s (READ )
[parent 0] time:  6.724, bw:   18554 KiB/s (TOTAL)

=== bandwidth limit: 24MiB/s (token bucket) ===
[task   2] time:  3.215, bw:    9765 KiB/s (WRITE)
[task   2] time:  2.767, bw:   11718 KiB/s (READ )
[task   1] time:  2.615, bw:   11718 KiB/s (WRITE)
[task   1] time:  3.958, bw:    7812 KiB/s (READ )
[parent 0] time:  6.610, bw:   19531 KiB/s (TOTAL)

In conclusion, results seem to confirm that leaky bucket is more precise
(more smoothed) than token bucket; token bucket, instead, is better in
terms of efficiency when approaching to the disk's I/O physical limit,
as the theory claims.

It would be also interesting to test how token bucket performance
changes using different bucket size values. I'll do more accurate tests
ASAP.

Signed-off-by: Andrea Righi <righi.andrea@...il.com>
---
 block/Makefile                  |    2 +
 block/blk-io-throttle.c         |  490 +++++++++++++++++++++++++++++++++++++++
 include/linux/blk-io-throttle.h |   12 +
 include/linux/cgroup_subsys.h   |    6 +
 init/Kconfig                    |   10 +
 5 files changed, 520 insertions(+), 0 deletions(-)

diff --git a/block/Makefile b/block/Makefile
index 5a43c7d..8dec69b 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -14,3 +14,5 @@ obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 
 obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
 obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o
+
+obj-$(CONFIG_CGROUP_IO_THROTTLE)	+= blk-io-throttle.o
diff --git a/block/blk-io-throttle.c b/block/blk-io-throttle.c
new file mode 100644
index 0000000..c6af273
--- /dev/null
+++ b/block/blk-io-throttle.c
@@ -0,0 +1,490 @@
+/*
+ * blk-io-throttle.c
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ *
+ * Copyright (C) 2008 Andrea Righi <righi.andrea@...il.com>
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/cgroup.h>
+#include <linux/slab.h>
+#include <linux/gfp.h>
+#include <linux/err.h>
+#include <linux/sched.h>
+#include <linux/fs.h>
+#include <linux/jiffies.h>
+#include <linux/hardirq.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/blk-io-throttle.h>
+
+#define ONE_SEC 1000000L /* # of microseconds in a second */
+#define KBS(x) ((x) * ONE_SEC >> 10)
+
+struct iothrottle_node {
+	struct list_head node;
+	dev_t dev;
+	unsigned long iorate;
+	unsigned long timestamp;
+	atomic_long_t stat;
+	long bucket_size;
+	atomic_long_t token;
+};
+
+struct iothrottle {
+	struct cgroup_subsys_state css;
+	/* protects the list below, not the single elements */
+	spinlock_t lock;
+	struct list_head list;
+	int strategy;
+};
+
+static inline struct iothrottle *cgroup_to_iothrottle(struct cgroup *cont)
+{
+	return container_of(cgroup_subsys_state(cont, iothrottle_subsys_id),
+			    struct iothrottle, css);
+}
+
+static inline struct iothrottle *task_to_iothrottle(struct task_struct *task)
+{
+	return container_of(task_subsys_state(task, iothrottle_subsys_id),
+			    struct iothrottle, css);
+}
+
+static inline struct iothrottle_node *iothrottle_search_node(
+					const struct iothrottle *iot,
+					dev_t dev)
+{
+	struct iothrottle_node *n;
+
+	list_for_each_entry_rcu(n, &iot->list, node)
+		if (n->dev == dev)
+			return n;
+	return NULL;
+}
+
+static inline void iothrottle_insert_node(struct iothrottle *iot,
+					 struct iothrottle_node *n)
+{
+	list_add_rcu(&n->node, &iot->list);
+}
+
+static inline struct iothrottle_node *iothrottle_replace_node(
+					struct iothrottle *iot,
+					struct iothrottle_node *old,
+					struct iothrottle_node *new)
+{
+	list_replace_rcu(&old->node, &new->node);
+	return old;
+}
+
+static inline struct iothrottle_node *iothrottle_delete_node(
+					struct iothrottle *iot,
+					dev_t dev)
+{
+	struct iothrottle_node *n;
+
+	list_for_each_entry(n, &iot->list, node)
+		if (n->dev == dev) {
+			list_del_rcu(&n->node);
+			return n;
+		}
+	return NULL;
+}
+
+/*
+ * Note: called from kernel/cgroup.c with cgroup_lock() held.
+ */
+static struct cgroup_subsys_state *iothrottle_create(
+			struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	struct iothrottle *iot;
+
+	iot = kmalloc(sizeof(*iot), GFP_KERNEL);
+	if (unlikely(!iot))
+		return ERR_PTR(-ENOMEM);
+
+	INIT_LIST_HEAD(&iot->list);
+	spin_lock_init(&iot->lock);
+	iot->strategy = 0;
+
+	return &iot->css;
+}
+
+/*
+ * Note: called from kernel/cgroup.c with cgroup_lock() held.
+ */
+static void iothrottle_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	struct iothrottle_node *n, *p;
+	struct iothrottle *iot = cgroup_to_iothrottle(cont);
+
+	/*
+	 * don't worry about locking here, at this point there must be not any
+	 * reference to the list.
+	 */
+	list_for_each_entry_safe(n, p, &iot->list, node)
+		kfree(n);
+	kfree(iot);
+}
+
+static ssize_t iothrottle_read(struct cgroup *cont,
+			       struct cftype *cft,
+			       struct file *file,
+			       char __user *userbuf,
+			       size_t nbytes,
+			       loff_t *ppos)
+{
+	struct iothrottle *iot;
+	char *buffer;
+	int s = 0;
+	struct iothrottle_node *n;
+	ssize_t ret;
+
+	buffer = kmalloc(nbytes + 1, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	cgroup_lock();
+	if (cgroup_is_removed(cont)) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	iot = cgroup_to_iothrottle(cont);
+	rcu_read_lock();
+	list_for_each_entry_rcu(n, &iot->list, node) {
+		unsigned long delta, rate;
+
+		BUG_ON(!n->dev);
+		delta = jiffies_to_usecs((long)jiffies - (long)n->timestamp);
+		rate = delta ? KBS(atomic_long_read(&n->stat) / delta) : 0;
+		s += scnprintf(buffer + s, nbytes - s,
+			       "device: %u,%u\n"
+			       "bandwidth: %lu KiB/sec\n"
+			       "usage: %lu KiB/sec\n"
+			       "bucket size: %lu KiB\n"
+			       "bucket fill: %li KiB\n",
+			       MAJOR(n->dev), MINOR(n->dev),
+			       n->iorate, rate,
+			       n->bucket_size,
+			       atomic_long_read(&n->token) >> 10);
+	}
+	rcu_read_unlock();
+	ret = simple_read_from_buffer(userbuf, nbytes, ppos, buffer, s);
+out:
+	cgroup_unlock();
+	kfree(buffer);
+	return ret;
+}
+
+static inline dev_t devname2dev_t(const char *buf)
+{
+	struct block_device *bdev;
+	dev_t ret;
+
+	bdev = lookup_bdev(buf);
+	if (IS_ERR(bdev))
+		return 0;
+
+	BUG_ON(!bdev->bd_inode);
+	ret = bdev->bd_inode->i_rdev;
+	bdput(bdev);
+
+	return ret;
+}
+
+static inline int iothrottle_parse_args(char *buf, size_t nbytes,
+					dev_t *dev, unsigned long *iorate,
+					unsigned long *bucket_size)
+{
+	char *ioratep, *bucket_sizep;
+
+	ioratep = memchr(buf, ':', nbytes);
+	if (!ioratep)
+		return -EINVAL;
+	*ioratep++ = '\0';
+
+	bucket_sizep = memchr(ioratep, ':', nbytes + ioratep - buf);
+	if (!bucket_sizep)
+		return -EINVAL;
+	*bucket_sizep++ = '\0';
+
+	/* i/o bandiwth is expressed in KiB/s */
+	*iorate = ALIGN(memparse(ioratep, &ioratep), 1024) >> 10;
+	if (*ioratep)
+		return -EINVAL;
+	*bucket_size = ALIGN(memparse(bucket_sizep, &bucket_sizep), 1024) >> 10;
+	if (*bucket_sizep)
+		return -EINVAL;
+
+	*dev = devname2dev_t(buf);
+	if (!*dev)
+		return -ENOTBLK;
+
+	return 0;
+}
+
+static ssize_t iothrottle_write(struct cgroup *cont,
+				struct cftype *cft,
+				struct file *file,
+				const char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	struct iothrottle *iot;
+	struct iothrottle_node *n, *tmpn = NULL;
+	char *buffer, *tmpp;
+	dev_t dev;
+	unsigned long iorate, bucket_size;
+	int ret;
+
+	if (!nbytes)
+		return -EINVAL;
+
+	/* Upper limit on largest io-throttle rule string user might write. */
+	if (nbytes > 1024)
+		return -E2BIG;
+
+	buffer = kmalloc(nbytes + 1, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	if (copy_from_user(buffer, userbuf, nbytes)) {
+		ret = -EFAULT;
+		goto out1;
+	}
+
+	buffer[nbytes] = '\0';
+	tmpp = strstrip(buffer);
+
+	ret = iothrottle_parse_args(tmpp, nbytes, &dev, &iorate, &bucket_size);
+	if (ret)
+		goto out1;
+
+	if (iorate) {
+		tmpn = kmalloc(sizeof(*tmpn), GFP_KERNEL);
+		if (!tmpn) {
+			ret = -ENOMEM;
+			goto out1;
+		}
+		atomic_long_set(&tmpn->stat, 0);
+		tmpn->timestamp = jiffies;
+		tmpn->iorate = iorate;
+		tmpn->bucket_size = bucket_size;
+		atomic_long_set(&tmpn->token, 0);
+		tmpn->dev = dev;
+	}
+
+	cgroup_lock();
+	if (cgroup_is_removed(cont)) {
+		ret = -ENODEV;
+		goto out2;
+	}
+
+	iot = cgroup_to_iothrottle(cont);
+	spin_lock(&iot->lock);
+	if (!iorate) {
+		/* Delete a block device limiting rule */
+		n = iothrottle_delete_node(iot, dev);
+		goto out3;
+	}
+	n = iothrottle_search_node(iot, dev);
+	if (n) {
+		/* Update a block device limiting rule */
+		iothrottle_replace_node(iot, n, tmpn);
+		goto out3;
+	}
+	/* Add a new block device limiting rule */
+	iothrottle_insert_node(iot, tmpn);
+out3:
+	ret = nbytes;
+	spin_unlock(&iot->lock);
+	if (n) {
+		synchronize_rcu();
+		kfree(n);
+	}
+out2:
+	cgroup_unlock();
+out1:
+	kfree(buffer);
+	return ret;
+}
+
+static s64 iothrottle_strategy_read(struct cgroup *cont, struct cftype *cft)
+{
+	struct iothrottle *iot;
+	s64 ret;
+
+	cgroup_lock();
+	if (cgroup_is_removed(cont)) {
+		cgroup_unlock();
+		return -ENODEV;
+	}
+	iot = cgroup_to_iothrottle(cont);
+	ret = iot->strategy;
+	cgroup_unlock();
+	return ret;
+}
+
+static int iothrottle_strategy_write(struct cgroup *cont,
+				     struct cftype *cft, s64 val)
+{
+	struct iothrottle *iot;
+
+	cgroup_lock();
+	if (cgroup_is_removed(cont)) {
+		cgroup_unlock();
+		return -ENODEV;
+	}
+	iot = cgroup_to_iothrottle(cont);
+	iot->strategy = (int)val;
+	cgroup_unlock();
+	return 0;
+}
+
+static struct cftype files[] = {
+	{
+		.name = "bandwidth",
+		.read = iothrottle_read,
+		.write = iothrottle_write,
+	},
+	{
+		.name = "throttling_strategy",
+		.read_s64 = iothrottle_strategy_read,
+		.write_s64 = iothrottle_strategy_write,
+	},
+};
+
+static int iothrottle_populate(struct cgroup_subsys *ss, struct cgroup *cont)
+{
+	return cgroup_add_files(cont, ss, files, ARRAY_SIZE(files));
+}
+
+struct cgroup_subsys iothrottle_subsys = {
+	.name = "blockio",
+	.create = iothrottle_create,
+	.destroy = iothrottle_destroy,
+	.populate = iothrottle_populate,
+	.subsys_id = iothrottle_subsys_id,
+};
+
+static inline int __cant_sleep(void)
+{
+	return in_atomic() || in_interrupt() || irqs_disabled();
+}
+
+static long leaky_bucket(struct iothrottle_node *n, size_t bytes)
+{
+	unsigned long delta, t;
+	long sleep;
+
+	/* Account the i/o activity */
+	atomic_long_add(bytes, &n->stat);
+
+	/* Evaluate if we need to throttle the current process */
+	delta = (long)jiffies - (long)n->timestamp;
+	if (!delta)
+		return 0;
+
+	t = usecs_to_jiffies(KBS(atomic_long_read(&n->stat) / n->iorate));
+	if (!t)
+		return 0;
+
+	sleep = t - delta;
+	if (unlikely(sleep > 0))
+		return sleep;
+
+	/* Reset i/o statistics */
+	atomic_long_set(&n->stat, 0);
+	/*
+	 * NOTE: be sure i/o statistics have been resetted before updating the
+	 * timestamp, otherwise a very small time delta may possibly be read by
+	 * another CPU w.r.t. accounted i/o statistics, generating unnecessary
+	 * long sleeps.
+	 */
+	smp_wmb();
+	n->timestamp = jiffies;
+	return 0;
+}
+
+/* XXX: need locking in order to evaluate a consistent sleep??? */
+static long token_bucket(struct iothrottle_node *n, size_t bytes)
+{
+	unsigned long delta;
+	long tok;
+
+	atomic_long_sub(bytes, &n->token);
+
+	delta = (long)jiffies - (long)n->timestamp;
+	if (!delta)
+		return 0;
+
+	n->timestamp = jiffies;
+	tok = atomic_long_read(&n->token) + jiffies_to_msecs(delta) * n->iorate;
+	if (tok > n->bucket_size)
+		tok = n->bucket_size;
+	atomic_long_set(&n->token, tok);
+
+	return (tok < 0) ? msecs_to_jiffies(-tok / n->iorate) : 0;
+}
+
+void cgroup_io_throttle(struct block_device *bdev, size_t bytes)
+{
+	struct iothrottle *iot;
+	struct iothrottle_node *n;
+	long sleep;
+
+	if (unlikely(!bdev || !bytes))
+		return;
+
+	iot = task_to_iothrottle(current);
+	if (unlikely(!iot))
+		return;
+
+	BUG_ON(!bdev->bd_inode);
+
+	rcu_read_lock();
+	n = iothrottle_search_node(iot, bdev->bd_inode->i_rdev);
+	if (!n || !n->iorate) {
+		rcu_read_unlock();
+		return;
+	}
+	switch (iot->strategy) {
+	case 0:
+		sleep = leaky_bucket(n, bytes);
+		break;
+	case 1:
+		sleep = token_bucket(n, bytes);
+		break;
+	default:
+		sleep = 0;
+	}
+	if (unlikely(sleep)) {
+		rcu_read_unlock();
+		if (__cant_sleep())
+			return;
+		pr_debug("io-throttle: task %p (%s) must sleep %lu jiffies\n",
+			 current, current->comm, sleep);
+		schedule_timeout_killable(sleep);
+		return;
+	}
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(cgroup_io_throttle);
diff --git a/include/linux/blk-io-throttle.h b/include/linux/blk-io-throttle.h
new file mode 100644
index 0000000..3e08738
--- /dev/null
+++ b/include/linux/blk-io-throttle.h
@@ -0,0 +1,12 @@
+#ifndef BLK_IO_THROTTLE_H
+#define BLK_IO_THROTTLE_H
+
+#ifdef CONFIG_CGROUP_IO_THROTTLE
+extern void cgroup_io_throttle(struct block_device *bdev, size_t bytes);
+#else
+static inline void cgroup_io_throttle(struct block_device *bdev, size_t bytes)
+{
+}
+#endif /* CONFIG_CGROUP_IO_THROTTLE */
+
+#endif /* BLK_IO_THROTTLE_H */
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index e287745..0caf3c2 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -48,3 +48,9 @@ SUBSYS(devices)
 #endif
 
 /* */
+
+#ifdef CONFIG_CGROUP_IO_THROTTLE
+SUBSYS(iothrottle)
+#endif
+
+/* */
diff --git a/init/Kconfig b/init/Kconfig
index 6199d11..3117d99 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -306,6 +306,16 @@ config CGROUP_DEVICE
 	  Provides a cgroup implementing whitelists for devices which
 	  a process in the cgroup can mknod or open.
 
+config CGROUP_IO_THROTTLE
+	bool "Enable cgroup I/O throttling (EXPERIMENTAL)"
+	depends on CGROUPS && EXPERIMENTAL
+	help
+	  This allows to limit the maximum I/O bandwidth for specific
+	  cgroup(s).
+	  See Documentation/controllers/io-throttle.txt for more information.
+
+	  If unsure, say N.
+
 config CPUSETS
 	bool "Cpuset support"
 	depends on SMP && CGROUPS
--
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