From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Rientjes <rientjes@google.com>
Subject: Re: [Bug #13319] Page allocation failures with b43 and p54usb
Date: Mon, 29 Jun 2009 22:47:03 -0700 (PDT)
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To: Larry Finger <Larry.Finger@lwfinger.net>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Kernel Testers List <kernel-testers@vger.kernel.org>, Johannes Berg <johannes@sipsolutions.net>, Pekka Enberg <penberg@cs.helsinki.fi>, Christoph Lameter <cl@linux-foundation.org>

On Mon, 29 Jun 2009, Larry Finger wrote:

> > I'd disagree with disabling slub debugging by default for caches where 
> > oo_order(s->min) increases as the result of using it.  This particular 
> > page allocation failure is happening for, presumably, kmalloc-4096, and 
> > the system has 4K pages.  Disabling debugging for that cache (and any of 
> > its aliases) implicitly will lead to errors going undiagnosed as a result.
> 
> If the current behavior is not changed, I will be forced to disable
> SLUB debugging, which will explicitly lead to errors that are
> undiagnosed.

You're buying debugging support at the cost of increased memory 
consumption when you enable CONFIG_SLUB_DEBUG_ON and that's causing the 
page allocation failures because of fragmentation.  To reduce the minimum 
order required for caches such as kmalloc-4096, you'd have to disable 
debugging for that particular cache.  It's my opinion that such a 
configuration should not be the default, however.

You could argue adding `slub_debug=-,kmalloc-4096' support from the 
command line, but CONFIG_SLUB_DEBUG_ON should not change its well-defined 
purpose of enabling debugging on all slab caches.  Otherwise the rest of 
us would be forced to add `slub_debug=,kmalloc-4096' for consistent 
behavior with older kernels.