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

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Message-ID: <20091125145410.GJ9482@parisc-linux.org>
Date:	Wed, 25 Nov 2009 07:54:11 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Liuweni <qingshenlwy@...il.com>
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

On Wed, Nov 25, 2009 at 10:51:33PM +0800, Liuweni wrote:
> 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;

If 'counter' has the value 0xffffffff, and the loop increments 'counter'
to zero, this check needs to be inside the loop.

> 
> -----------
> Best Regards,
> Liuweni 
> 2009-11-25 
> 
> 
> 
> 
> 
> 
> 
> ???????? Matthew Wilcox 
> ?????????? 2009-11-25  22:15:09 
> ???????? Liuweni 
> ?????? linux-kernel; strongzgy; xgr178; Liu Hui; viro; akpm; jack; npiggin; linux-fsdevel 
> ?????? 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
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> -- 
> 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."

-- 
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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