linux-kernel - Re: [PATCH 2/3] slub: record page flag overlays explicitly

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Message-ID: <20080527145250.GA3407@shadowen.org>
Date:	Tue, 27 May 2008 15:53:03 +0100
From:	apw@...dowen.org
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...l.org>,
	Christoph Lameter <clameter@....com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] slub: record page flag overlays explicitly

On Mon, May 26, 2008 at 01:40:44PM +0900, KOSAKI Motohiro wrote:
> Hi
> 
> This patch works well on my box.
> but I have one question.
> 
> >  	if (s->flags & DEBUG_DEFAULT_FLAGS) {
> > -		if (!SlabDebug(page))
> > -			printk(KERN_ERR "SLUB %s: SlabDebug not set "
> > +		if (!PageSlubDebug(page))
> > +			printk(KERN_ERR "SLUB %s: SlubDebug not set "
> >  				"on slab 0x%p\n", s->name, page);
> >  	} else {
> > -		if (SlabDebug(page))
> > -			printk(KERN_ERR "SLUB %s: SlabDebug set on "
> > +		if (PageSlubDebug(page))
> > +			printk(KERN_ERR "SLUB %s: SlubDebug set on "
> >  				"slab 0x%p\n", s->name, page);
> >  	}
> >  }
> 
> Why if(SLABDEBUG) check is unnecessary?

They were unconditional before as well.  SlabDebug would always return
0 before the patch.  The point being, to my reading, that if you asked
for debug on the slab and debug was not compiled in you would still get
told that it was not set; which it cannot without the support.

-apw
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