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Date: Wed, 26 Apr 2006 15:20:30 +0800
From: Akinobu Mita <mita@miraclelinux.com>
To: Greg KH <greg@kroah.com>
Cc: Jens Axboe <axboe@suse.de>, Al Viro <viro@ftp.linux.org.uk>,
       linux-kernel@vger.kernel.org, akpm@osdl.org,
       Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [patch 3/3] use kref for bio
Message-ID: <20060426072030.GA7693@miraclelinux.com>
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On Tue, Apr 25, 2006 at 10:18:13PM -0700, Greg KH wrote:
> > > Let's _not_.  It's extra overhead for no good reason.
> > 
> > Completely agree. That goes for the other block layer kref patches as
> > well.
> 
> I also agree, there's a reason I never tried to convert them in the past
> :)

kref has faster function for decrement refcount.

kref_put()
{
...

	/*
	 * if current count is one, we are the last user and can release object
	 * right now, avoiding an atomic operation on 'refcount'
	 */
	if ((atomic_read(&kref->refcount) == 1) ||
		(atomic_dec_and_test(&kref->refcount))) {
		release(kref);
		return 1;
	}

If this is good one and the places where Al Viro pointed out really affect
performance, should we propagate this faster one by introducing helper
function like:

static inline int refcount_test(atomic_t *refcount)
{
	return (atomic_read(refcount) == 1) || (atomic_dec_and_test(refcount));
}

and replace atomic_dec_and_test with it?