Re: [PATCH 2/3] i/o bandwidth controller infrastructure

[Li Zefan <lizf@cn.fujitsu.com>]

> +/**
> + * 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;
> +}