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

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Date:	Wed, 25 Nov 2009 22:51:33 +0800
From:	"Liuweni" <qingshenlwy@...il.com>
To:	"Matthew Wilcox" <matthew@....cx>
Cc:	"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>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"strongzgy" <strongzgy@...il.com>, "xgr178" <xgr178@....com>,
	"Liu Hui" <onlyflyer@...il.com>
Subject: Re: [PATCH 1/3]fs/inode: iunique() Optimize Performance

Hi  Matthew Wilcox ,
    The code means set counter's value to the max max_reserved and counter.
Then, the if condition will choose a large one, and in the function, the counter
is increased. so this code won't change the function of iunique().

> + if (counter <= max_reserved)
> + counter = max_reserved + 1;


-----------
Best Regards,
Liuweni 
2009-11-25 







发件人： Matthew Wilcox 
发送时间： 2009-11-25  22:15:09 
收件人： Liuweni 
抄送： linux-kernel; strongzgy; xgr178; Liu Hui; viro; akpm; jack; npiggin; linux-fsdevel 
主题： 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."