[PATCH] make iunique use a do/while loop rather than its obscure goto loop

[PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Jeffrey Layton]

While working on a case, Christoph mentioned that he thought that iunique
ought to be cleaned up to use a more conventional loop construct. This patch
does that, turning the strange goto loop into a do/while.

Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/fs/inode.c b/fs/inode.c
index 23fc1fd..90e7587 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
 	struct inode *inode;
 	struct hlist_head * head;
 	ino_t res;
+
 	spin_lock(&inode_lock);
-retry:
-	if (counter > max_reserved) {
-		head = inode_hashtable + hash(sb,counter);
+	do {
+		if (counter <= max_reserved)
+			counter = max_reserved + 1;
 		res = counter++;
+		head = inode_hashtable + hash(sb, res);
 		inode = find_inode_fast(sb, head, res);
-		if (!inode) {
-			spin_unlock(&inode_lock);
-			return res;
-		}
-	} else {
-		counter = max_reserved + 1;
-	}
-	goto retry;
-	
+	} while (inode != NULL);
+	spin_unlock(&inode_lock);
+
+	return res;
 }
 
 EXPORT_SYMBOL(iunique);

Re: [PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Christoph Hellwig]

On Tue, Jan 30, 2007 at 10:45:54AM -0500, Jeffrey Layton wrote:
> While working on a case, Christoph mentioned that he thought that iunique
> ought to be cleaned up to use a more conventional loop construct. This patch
> does that, turning the strange goto loop into a do/while.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 23fc1fd..90e7587 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
>  	struct inode *inode;
>  	struct hlist_head * head;
>  	ino_t res;
> +
>  	spin_lock(&inode_lock);
> -retry:
> -	if (counter > max_reserved) {
> -		head = inode_hashtable + hash(sb,counter);
> +	do {
> +		if (counter <= max_reserved)
> +			counter = max_reserved + 1;
>  		res = counter++;
> +		head = inode_hashtable + hash(sb, res);
>  		inode = find_inode_fast(sb, head, res);
> -		if (!inode) {
> -			spin_unlock(&inode_lock);
> -			return res;
> -		}
> -	} else {
> -		counter = max_reserved + 1;
> -	}
> -	goto retry;
> -	
> +	} while (inode != NULL);
> +	spin_unlock(&inode_lock);
> +
> +	return res;

Looks good, thanks

[PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Jeffrey Layton]

A while back, Christoph mentioned that he thought that iunique ought to be
cleaned up to use a more conventional loop construct. This patch does that,
turning the strange goto loop into a do/while.

Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/fs/inode.c b/fs/inode.c
index 23fc1fd..90e7587 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
 	struct inode *inode;
 	struct hlist_head * head;
 	ino_t res;
+
 	spin_lock(&inode_lock);
-retry:
-	if (counter > max_reserved) {
-		head = inode_hashtable + hash(sb,counter);
+	do {
+		if (counter <= max_reserved)
+			counter = max_reserved + 1;
 		res = counter++;
+		head = inode_hashtable + hash(sb, res);
 		inode = find_inode_fast(sb, head, res);
-		if (!inode) {
-			spin_unlock(&inode_lock);
-			return res;
-		}
-	} else {
-		counter = max_reserved + 1;
-	}
-	goto retry;
-	
+	} while (inode != NULL);
+	spin_unlock(&inode_lock);
+
+	return res;
 }
 
 EXPORT_SYMBOL(iunique);

Re: [PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Andrew Morton]

On Wed, 11 Apr 2007 17:58:56 -0400
Jeffrey Layton <jlayton@redhat.com> wrote:

> A while back, Christoph mentioned that he thought that iunique ought to be
> cleaned up to use a more conventional loop construct. This patch does that,
> turning the strange goto loop into a do/while.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 23fc1fd..90e7587 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
>  	struct inode *inode;
>  	struct hlist_head * head;
>  	ino_t res;
> +
>  	spin_lock(&inode_lock);
> -retry:
> -	if (counter > max_reserved) {
> -		head = inode_hashtable + hash(sb,counter);
> +	do {
> +		if (counter <= max_reserved)
> +			counter = max_reserved + 1;
>  		res = counter++;
> +		head = inode_hashtable + hash(sb, res);
>  		inode = find_inode_fast(sb, head, res);
> -		if (!inode) {
> -			spin_unlock(&inode_lock);
> -			return res;
> -		}
> -	} else {
> -		counter = max_reserved + 1;
> -	}
> -	goto retry;
> -	
> +	} while (inode != NULL);
> +	spin_unlock(&inode_lock);
> +
> +	return res;
>  }
>  

hm.

ino_t iunique(struct super_block *sb, ino_t max_reserved)
{
	static ino_t counter;
	struct inode *inode;
	struct hlist_head * head;
	ino_t res;

	spin_lock(&inode_lock);
	do {
		if (counter <= max_reserved)
			counter = max_reserved + 1;
		res = counter++;
		head = inode_hashtable + hash(sb, res);
		inode = find_inode_fast(sb, head, res);
	} while (inode != NULL);
	spin_unlock(&inode_lock);

	return res;
}

The counter-vs-max_reserved test can be moved outside the loop, can't it?

Shouldn't counter be per-sb?

Re: [PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Jeff Layton]

Andrew Morton wrote:
> On Wed, 11 Apr 2007 17:58:56 -0400
> Jeffrey Layton <jlayton@redhat.com> wrote:
> 
>> A while back, Christoph mentioned that he thought that iunique ought to be
>> cleaned up to use a more conventional loop construct. This patch does that,
>> turning the strange goto loop into a do/while.
>>
>> Signed-off-by: Jeff Layton <jlayton@redhat.com>
>>
>> diff --git a/fs/inode.c b/fs/inode.c
>> index 23fc1fd..90e7587 100644
>> --- a/fs/inode.c
>> +++ b/fs/inode.c
>> @@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
>>  	struct inode *inode;
>>  	struct hlist_head * head;
>>  	ino_t res;
>> +
>>  	spin_lock(&inode_lock);
>> -retry:
>> -	if (counter > max_reserved) {
>> -		head = inode_hashtable + hash(sb,counter);
>> +	do {
>> +		if (counter <= max_reserved)
>> +			counter = max_reserved + 1;
>>  		res = counter++;
>> +		head = inode_hashtable + hash(sb, res);
>>  		inode = find_inode_fast(sb, head, res);
>> -		if (!inode) {
>> -			spin_unlock(&inode_lock);
>> -			return res;
>> -		}
>> -	} else {
>> -		counter = max_reserved + 1;
>> -	}
>> -	goto retry;
>> -	
>> +	} while (inode != NULL);
>> +	spin_unlock(&inode_lock);
>> +
>> +	return res;
>>  }
>>  
> 
> hm.
> 
> ino_t iunique(struct super_block *sb, ino_t max_reserved)
> {
> 	static ino_t counter;
> 	struct inode *inode;
> 	struct hlist_head * head;
> 	ino_t res;
> 
> 	spin_lock(&inode_lock);
> 	do {
> 		if (counter <= max_reserved)
> 			counter = max_reserved + 1;
> 		res = counter++;
> 		head = inode_hashtable + hash(sb, res);
> 		inode = find_inode_fast(sb, head, res);
> 	} while (inode != NULL);
> 	spin_unlock(&inode_lock);
> 
> 	return res;
> }
> 
> The counter-vs-max_reserved test can be moved outside the loop, can't it?
> 

No. If the counter wraps while we're looping, then we'll need to skip 
past the "reserved" inode numbers. So we need to check this on every 
loop iteration. We could potentially put that in an "unlikely" if you 
think that would be better.

> Shouldn't counter be per-sb?

I doubt it really matters too much, but it could potentially be more 
efficient to do that, especially after a wraparound on the counter. It 
might be reasonable to make new_inode use a per-sb counter as well. Do 
you think it's worth respinning?

-- Jeff

Re: [PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Andrew Morton]

On Fri, 13 Apr 2007 15:08:38 -0400
Jeff Layton <jlayton@redhat.com> wrote:

> > 
> > ino_t iunique(struct super_block *sb, ino_t max_reserved)
> > {
> > 	static ino_t counter;
> > 	struct inode *inode;
> > 	struct hlist_head * head;
> > 	ino_t res;
> > 
> > 	spin_lock(&inode_lock);
> > 	do {
> > 		if (counter <= max_reserved)
> > 			counter = max_reserved + 1;
> > 		res = counter++;
> > 		head = inode_hashtable + hash(sb, res);
> > 		inode = find_inode_fast(sb, head, res);
> > 	} while (inode != NULL);
> > 	spin_unlock(&inode_lock);
> > 
> > 	return res;
> > }
> > 
> > The counter-vs-max_reserved test can be moved outside the loop, can't it?
> > 
> 
> No. If the counter wraps while we're looping, then we'll need to skip 
> past the "reserved" inode numbers. So we need to check this on every 
> loop iteration.

oh.

(wonders why alpha and s390 use unsigned int for ino_t while everyone
else uses unsigned long)

> We could potentially put that in an "unlikely" if you 
> think that would be better.

Doubt if it'd make much difference.

> > Shouldn't counter be per-sb?
> 
> I doubt it really matters too much, but it could potentially be more 
> efficient to do that, especially after a wraparound on the counter. It 
> might be reasonable to make new_inode use a per-sb counter as well. Do 
> you think it's worth respinning?

Well, that'd be a separate patch.  Sometime, if you're keen.

If that function is ever a performance problem, it'll be an awful
performance problem and we'd need to so something smarter than
a linear search - an idr tree, for example.

Re: [PATCH] make iunique use a do/while loop rather than its obscure goto loop

[Christoph Hellwig]

On Wed, Apr 11, 2007 at 05:58:56PM -0400, Jeffrey Layton wrote:
> A while back, Christoph mentioned that he thought that iunique ought to be
> cleaned up to use a more conventional loop construct. This patch does that,
> turning the strange goto loop into a do/while.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 23fc1fd..90e7587 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -689,21 +689,18 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
>  	struct inode *inode;
>  	struct hlist_head * head;
>  	ino_t res;
> +
>  	spin_lock(&inode_lock);
> -retry:
> -	if (counter > max_reserved) {
> -		head = inode_hashtable + hash(sb,counter);
> +	do {
> +		if (counter <= max_reserved)
> +			counter = max_reserved + 1;
>  		res = counter++;
> +		head = inode_hashtable + hash(sb, res);
>  		inode = find_inode_fast(sb, head, res);
> -		if (!inode) {
> -			spin_unlock(&inode_lock);
> -			return res;
> -		}
> -	} else {
> -		counter = max_reserved + 1;
> -	}
> -	goto retry;
> -	
> +	} while (inode != NULL);
> +	spin_unlock(&inode_lock);
> +
> +	return res;
>  }
>  
>  EXPORT_SYMBOL(iunique);
---end quoted text---