Date:	Sat, 05 Jul 2008 17:21:44 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Li Zefan <lizf@...fujitsu.com>
CC:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Carl Henrik Lunde <chlunde@...g.uio.no>, axboe@...nel.dk,
	matt@...ehost.com, roberto@...it.it, randy.dunlap@...cle.com,
	Divyesh Shah <dpshah@...gle.com>, subrata@...ux.vnet.ibm.com,
	eric.rannaud@...il.com, akpm@...ux-foundation.org,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] i/o bandwidth controller infrastructure

Li Zefan wrote:
>> +/**
>> + * struct iothrottle_node - throttling rule of a single block device
>> + * @node: list of per block device throttling rules
>> + * @dev: block device number, used as key in the list
>> + * @iorate: max i/o bandwidth (in bytes/s)
>> + * @strategy: throttling strategy (0 = leaky bucket, 1 = token bucket)
> 
> use enum or define
> 
>> + * @timestamp: timestamp of the last I/O request (in jiffies)
>> + * @stat: i/o activity counter (leaky bucket only)
>> + * @bucket_size: bucket size in bytes (token bucket only)
>> + * @token: token counter (token bucket only)
>> + *
>> + * Define a i/o throttling rule for a single block device.
>> + *
>> + * NOTE: limiting rules always refer to dev_t; if a block device is unplugged
>> + * the limiting rules defined for that device persist and they are still valid
>> + * if a new device is plugged and it uses the same dev_t number.
>> + */
>> +struct iothrottle_node {
>> +	struct list_head node;
>> +	dev_t dev;
>> +	u64 iorate;
>> +	long strategy;
>> +	unsigned long timestamp;
>> +	atomic_long_t stat;
>> +	s64 bucket_size;
>> +	atomic_long_t token;
>> +};
>> +
>> +/**
>> + * struct iothrottle - throttling rules for a cgroup
>> + * @css: pointer to the cgroup state
>> + * @lock: spinlock used to protect write operations in the list
>> + * @list: list of iothrottle_node elements
>> + *
>> + * Define multiple per-block device i/o throttling rules.
>> + * Note: the list of the throttling rules is protected by RCU locking.
>> + */
>> +struct iothrottle {
>> +	struct cgroup_subsys_state css;
>> +	spinlock_t lock;
>> +	struct list_head list;
>> +};
>> +
>> +static inline struct iothrottle *cgroup_to_iothrottle(struct cgroup *cont)
>> +{
> 
> cgrp is a preferable name to 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);
>> +}
>> +
>> +/*
>> + * Note: called with rcu_read_lock() held.
>> + */
>> +static 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;
>> +}
>> +
>> +/*
>> + * Note: called with iot->lock held.
>> + */
>> +static inline void iothrottle_insert_node(struct iothrottle *iot,
>> +						struct iothrottle_node *n)
>> +{
>> +	list_add_rcu(&n->node, &iot->list);
>> +}
>> +
>> +/*
>> + * Note: called with iot->lock held.
>> + */
>> +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;
> 
> you just return back 'old', so the return value is useless
> 
>> +}
>> +
>> +/*
>> + * Note: called with iot->lock held.
>> + */
>> +static struct iothrottle_node *
>> +iothrottle_delete_node(struct iothrottle *iot, dev_t dev)
>> +{
>> +	struct iothrottle_node *n;
>> +
>> +	list_for_each_entry_rcu(n, &iot->list, node)
> 
> list_for_each_entry()
> 
>> +		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);
>> +
>> +	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)
> 
> use read_seq_string can simplify this function:
> 	.read_seq_string = iothrottle_read
> 
>> +{
>> +	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;
>> +
>> +		BUG_ON(!n->dev);
>> +		delta = jiffies_to_msecs((long)jiffies - (long)n->timestamp);
>> +		s += scnprintf(buffer + s, nbytes - s,
>> +				"%u %u %llu %li %li %lli %li %lu\n",
>> +				MAJOR(n->dev), MINOR(n->dev), n->iorate,
>> +				n->strategy, atomic_long_read(&n->stat),
>> +				n->bucket_size, atomic_long_read(&n->token),
>> +				delta);
>> +	}
>> +	rcu_read_unlock();
>> +	ret = simple_read_from_buffer(userbuf, nbytes, ppos, buffer, s);
>> +out:
>> +	cgroup_unlock();
>> +	kfree(buffer);
>> +	return ret;
>> +}
>> +
>> +static dev_t devname2dev_t(const char *buf)
>> +{
>> +	struct block_device *bdev;
>> +	dev_t dev = 0;
>> +	struct gendisk *disk;
>> +	int part;
>> +
>> +	/* use a lookup to validate the block device */
>> +	bdev = lookup_bdev(buf);
>> +	if (IS_ERR(bdev))
>> +		return 0;
>> +
>> +	/* only entire devices are allowed, not single partitions */
>> +	disk = get_gendisk(bdev->bd_dev, &part);
>> +	if (disk && !part) {
>> +		BUG_ON(!bdev->bd_inode);
>> +		dev = bdev->bd_inode->i_rdev;
>> +	}
>> +	bdput(bdev);
>> +
>> +	return dev;
>> +}
>> +
>> +/*
>> + * The userspace input string must use the following syntax:
>> + *
>> + * device:bw-limit:strategy:bucket-size
>> + */
> 
> why not support these syntax:
> device:0
> device:bw-limit:0
> 
>> +static int iothrottle_parse_args(char *buf, size_t nbytes,
>> +					dev_t *dev, u64 *iorate,
>> +					long *strategy, s64 *bucket_size)
>> +{
>> +	char *ioratep, *strategyp, *bucket_sizep;
>> +	int ret;
>> +
>> +	ioratep = memchr(buf, ':', nbytes);
>> +	if (!ioratep)
>> +		return -EINVAL;
>> +	*ioratep++ = '\0';
>> +
>> +	strategyp = memchr(ioratep, ':', buf + nbytes - ioratep);
>> +	if (!strategyp)
>> +		return -EINVAL;
>> +	*strategyp++ = '\0';
>> +
>> +	bucket_sizep = memchr(strategyp, ':', buf + nbytes - strategyp);
>> +	if (!bucket_sizep)
>> +		return -EINVAL;
>> +	*bucket_sizep++ = '\0';
>> +
>> +	/* i/o bandwidth limit (0 to delete a limiting rule) */
>> +	ret = strict_strtoull(ioratep, 10, iorate);
>> +	if (ret < 0)
>> +		return ret;
>> +	*iorate = ALIGN(*iorate, 1024);
>> +
>> +	/* throttling strategy */
>> +	ret = strict_strtol(strategyp, 10, strategy);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* bucket size */
>> +	ret = strict_strtoll(bucket_sizep, 10, bucket_size);
>> +	if (ret < 0)
>> +		return ret;
>> +	if (*bucket_size < 0)
>> +		return -EINVAL;
>> +	*bucket_size = ALIGN(*bucket_size, 1024);
>> +
>> +	/* block device number */
>> +	*dev = devname2dev_t(buf);
>> +	if (!*dev)
>> +		return -EINVAL;
>> +
>> +	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)
>> +{
> 
> you can use write_string (currently in -mm) to simplify this funciton:
> 	.write_string = iothrottle_write
> 
>> +	struct iothrottle *iot;
>> +	struct iothrottle_node *n, *newn = NULL;
>> +	char *buffer, *s;
>> +	dev_t dev;
>> +	u64 iorate;
>> +	long strategy;
>> +	s64 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;
>> +
>> +	ret = strncpy_from_user(buffer, userbuf, nbytes);
>> +	if (ret < 0)
>> +		goto out1;
>> +	buffer[nbytes] = '\0';
>> +	s = strstrip(buffer);
>> +
>> +	ret = iothrottle_parse_args(s, nbytes, &dev, &iorate,
>> +					&strategy, &bucket_size);
>> +	if (ret)
>> +		goto out1;
>> +
>> +	if (iorate) {
>> +		newn = kmalloc(sizeof(*newn), GFP_KERNEL);
>> +		if (!newn) {
>> +			ret = -ENOMEM;
>> +			goto out1;
>> +		}
>> +		newn->dev = dev;
>> +		newn->iorate = iorate;
>> +		newn->strategy = strategy;
>> +		newn->bucket_size = bucket_size;
>> +		newn->timestamp = jiffies;
>> +		atomic_long_set(&newn->stat, 0);
>> +		atomic_long_set(&newn->token, 0);
>> +	}
>> +
>> +	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, newn);
>> +		goto out3;
>> +	}
>> +	/* Add a new block device limiting rule */
>> +	iothrottle_insert_node(iot, newn);
>> +out3:
>> +	ret = nbytes;
>> +	spin_unlock(&iot->lock);
>> +	if (n) {
>> +		synchronize_rcu();
>> +		kfree(n);
>> +	}
>> +out2:
>> +	cgroup_unlock();
>> +out1:
>> +	kfree(buffer);
>> +	return ret;
>> +}

Li, thanks for reviewing. I agree on everything and I'll apply all your
suggestions in the next patchset version.

-Andrea
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