linux-kernel - Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance

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Date:	Wed, 25 Nov 2009 07:15:05 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Liuweni <qingshenlwy@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	strongzgy <strongzgy@...il.com>, xgr178 <xgr178@....com>,
	Liu Hui <onlyflyer@...il.com>, viro <viro@...iv.linux.org.uk>,
	akpm <akpm@...ux-foundation.org>, jack <jack@...e.cz>,
	npiggin <npiggin@...e.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance

On Wed, Nov 25, 2009 at 10:09:45PM +0800, Liuweni wrote:
> ---
> move the if condition out the while{}.
> While the function executing, the if 
> condition won't check again and again.
> And this code won't change the function
> of iunique().

That's not true.

> @@ -838,9 +838,10 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
>  	ino_t res;
>  
>  	spin_lock(&inode_lock);
> +
> +	if (counter <= max_reserved)
> +		counter = max_reserved + 1;
>  	do {
> -		if (counter <= max_reserved)
> -			counter = max_reserved + 1;
>  		res = counter++;

'counter' is incremented here, so if it wraps around, we'll blunder into 
the reserved space again.

>  		head = inode_hashtable + hash(sb, res);
>  		inode = find_inode_fast(sb, head, res);
> 
>  				
> --------------
> Best Regards,
> Liuweni
> 2009-11-25
> 
> --
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-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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