linux-kernel - Re: [mmotm] BUG: Bad page state in process khugepaged ?

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Date:	Mon, 14 Feb 2011 23:24:21 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [mmotm] BUG: Bad page state in process khugepaged ?

On Fri, Feb 11, 2011 at 11:49:06AM +0100, Andrea Arcangeli wrote:
> On Thu, Feb 10, 2011 at 11:02:50PM -0800, Hugh Dickins wrote:
> > There is a separate little issue here, Andrea.
> > 
> > Although we went to some trouble for bad_page() to take the page out
> > of circulation yet let the system continue, your VM_BUG_ON(!PageBuddy)
> > inside __ClearPageBuddy(page), from two callsites in bad_page(), is
> > turning it into a fatal error when CONFIG_DEBUG_VM.
> 
> I see what you mean. Of course it is only a problem after bad_page
> already triggered.... but then it trigger an BUG_ON instead of only a
> bad_page.
> 
> > You could that only MM developers switch CONFIG_DEBUG_VM=y, and they
> > would like bad_page() to be fatal; maybe, but if so we should do that
> > as an intentional patch, rather than as an unexpected side-effect ;)
> 
> Fedora kernels are built with CONFIG_DEBUG_VM, all my kernels runs
> with CONFIG_DEBUG_VM too, so we want it to be as "production" as
> possible, and we don't want DEBUG_VM to decrease any reliability (only
> to increase it of course).

Are you sure?

$ grep DEBUG_VM /boot/config-*
/boot/config-2.6.35.10-74.fc14.x86_64:# CONFIG_DEBUG_VM is not set
/boot/config-2.6.35.6-45.fc14.x86_64:# CONFIG_DEBUG_VM is not set

Only the one from the kernel-debug package has it set on this F14.

	Hannes
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