linux-kernel - Re: oops in copy_page

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Date:	Sun, 6 Jan 2013 19:37:18 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: oops in copy_page_rep()

On Sat, Jan 05, 2013 at 07:57:39PM -0800, Linus Torvalds wrote:
 > Adding more people in case somebody else has any idea. Anybody?
 > 
 > On Sat, Jan 5, 2013 at 7:22 AM, Dave Jones <davej@...hat.com> wrote:
 > > I have no idea what happened here, but this is the first time I've seen this one.
 > > This was running a tree pulled yesterday afternoon.
 > >
 > > BUG: unable to handle kernel paging request at ffff880100201000
 > 
 > This is %rsi, which is the source for the page copy:
 > 
 >   copy_user_highpage()->
 >     copy_user_page()->
 >       copy_page()->
 >         copy_page_rep
 > 
 > I don't know exactly which copy_user_highpage() case this is from, the
 > call trace implies this *could* be a hugepage, and those functions do
 > copy pages individually in a loop too.

investigating the huge page theory a little further I'm a bit confused.
The kernel on that machine has THP enabled, and the cpu supports it (an old amd64), but..

$ cat /sys/kernel/mm/hugepages/hugepages-2048kB/*
0
0
0
0
0
0

I was expecting at least one of those to be non-zero.

/sys/kernel/mm/transparent_hugepage/khugepaged/full_scans and pages_collapsed
are both non-zero, so it's been busy doing _something_.

Is this expected behaviour ?

	Dave

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