Re: [-mm PATCH 1/8] Memory controller resource counters (v2)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Dave Hansen wrote:
> On Thu, 2007-07-05 at 22:20 -0700, Balbir Singh wrote:
>> +/*
>> + * the core object. the container that wishes to account for some
>> + * resource may include this counter into its structures and use
>> + * the helpers described beyond
>> + */
> 
> I'm going to nitpick a bit here.  Nothing major, I promise. ;)
> 
> Could we make these comments into nice sentences with capitalization?  I
> think it makes them easier to read in long comments.
> 
> How about something like this for the comment:
> 
> /*
>  * A container wishing to account for a resource should include this
>  * structure into one of its own.  It may use the helpers below.
>  */
> 
> The one above is worded a little bit strangely.
> 

Hi, Dave,

These patches were posted by Pavel, I've carried them forward as is.
Suggestions are always welcome.

>> +struct res_counter {
>> +	/*
>> +	 * the current resource consumption level
>> +	 */
>> +	unsigned long usage;
>> +	/*
>> +	 * the limit that usage cannot exceed
>> +	 */
>> +	unsigned long limit;
>> +	/*
>> +	 * the number of insuccessful attempts to consume the resource
>> +	 */
> 
> unsuccessful
> 

Thanks, fixed.


>> +	unsigned long failcnt;
>> +	/*
>> +	 * the lock to protect all of the above.
>> +	 * the routines below consider this to be IRQ-safe
>> +	 */
>> +	spinlock_t lock;
>> +};
> 
> Do we really need all of these comments?  Some of them are a wee bit
> self-explanatory.  I think we mostly know what a limit is. ;)
> 

I'll leave the decision on the comments exclusion to Pavel.

> 
> More nitpicking...
> 
> Can we leave the normal control flow in the lowest indentation level,
> and have only errors in the indented if(){} blocks?  Something like
> this:
> 

Sounds good, done!

>> +int res_counter_charge_locked(struct res_counter *cnt, unsigned long
> val)
>> +{
>> +	if (cnt->usage > cnt->limit - val) {
>> +		cnt->failcnt++;
>> +		return -ENOMEM;
>> +	}
>> +	cnt->usage += val;
>> +	return 0;
>> +}
> 
> Also, can you do my poor brain a favor an expand "cnt" to "counter"?
> You're not saving _that_ much typing ;)
> 

Done

>> +int res_counter_charge(struct res_counter *cnt, unsigned long val)
>> +{
>> +	int ret;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&cnt->lock, flags);
>> +	ret = res_counter_charge_locked(cnt, val);
>> +	spin_unlock_irqrestore(&cnt->lock, flags);
>> +	return ret;
>> +}
>> +
>> +void res_counter_uncharge_locked(struct res_counter *cnt, unsigned long val)
>> +{
>> +	if (unlikely(cnt->usage < val)) {
>> +		WARN_ON(1);
>> +		val = cnt->usage;
>> +	}
>> +
>> +	cnt->usage -= val;
>> +}
> 
> It actually looks like the WARN_ON() macros "return" values.  You should
> be able to:
> 
> 	if (WARN_ON(cnt->usage < val))
> 		val = count->usage;
> 

I think, thats better, will change it

>> +void res_counter_uncharge(struct res_counter *cnt, unsigned long val)
>> +{
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&cnt->lock, flags);
>> +	res_counter_uncharge_locked(cnt, val);
>> +	spin_unlock_irqrestore(&cnt->lock, flags);
>> +}
>> +
>> +
>> +static inline unsigned long *res_counter_member(struct res_counter *cnt, int member)
>> +{
>> +	switch (member) {
>> +	case RES_USAGE:
>> +		return &cnt->usage;
>> +	case RES_LIMIT:
>> +		return &cnt->limit;
>> +	case RES_FAILCNT:
>> +		return &cnt->failcnt;
>> +	};
>> +
>> +	BUG();
>> +	return NULL;
>> +}
>>
>> +ssize_t res_counter_read(struct res_counter *cnt, int member,
>> +		const char __user *userbuf, size_t nbytes, loff_t *pos)
>> +{
>> +	unsigned long *val;
>> +	char buf[64], *s;
>> +
>> +	s = buf;
>> +	val = res_counter_member(cnt, member);
>> +	s += sprintf(s, "%lu\n", *val);
>> +	return simple_read_from_buffer((void __user *)userbuf, nbytes,
>> +			pos, buf, s - buf);
>> +}
> 
> Why do we need that cast?  
> 

u mean the __user? If I remember correctly it's a attribute for sparse.

>> +ssize_t res_counter_write(struct res_counter *cnt, int member,
>> +		const char __user *userbuf, size_t nbytes, loff_t *pos)
>> +{
>> +	int ret;
>> +	char *buf, *end;
>> +	unsigned long tmp, *val;
>> +
>> +	buf = kmalloc(nbytes + 1, GFP_KERNEL);
> 
> Do we need some checking on nbytes?  Is it sanitized before it gets
> here?
> 

I think the container infrastructure should handle that.

>> +	ret = -ENOMEM;
>> +	if (buf == NULL)
>> +		goto out;
>> +
>> +	buf[nbytes] = 0;
> 
> Please use '\0'.  0 isn't a char. 
> 

Yep, will do.

>> +	ret = -EFAULT;
>> +	if (copy_from_user(buf, userbuf, nbytes))
>> +		goto out_free;
>> +
>> +	ret = -EINVAL;
>> +	tmp = simple_strtoul(buf, &end, 10);
>> +	if (*end != '\0')
>> +		goto out_free;
>> +
>> +	val = res_counter_member(cnt, member);
>> +	*val = tmp;
>> +	ret = nbytes;
>> +out_free:
>> +	kfree(buf);
>> +out:
>> +	return ret;
>> +}
>> _
>>
> -- Dave
> 


-- 
	Thanks,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL