linux-kernel - Re: BUG: unable to handle kernel paging request at ffff8800cf669000

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Message-ID: <20110117065753.GD11358@cr0.nay.redhat.com>
Date:	Mon, 17 Jan 2011 14:57:53 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	xing lin <linxingnku@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel paging request at ffff8800cf669000

On Fri, Jan 14, 2011 at 04:30:51PM -0700, xing lin wrote:
>Hi,
>
>I wrote a kernel module to calculate the hash for each page frame, in
>order to see how many pages are duplicated. It works well in 32-bit
>Linux with 2GB physical memory. But when I tried to run this module in
>64-bit Linux(2.6.32-24-generic with NUMA enabled) with 12GB physical
>memory, it can calculates hashes for the first 63553 in-use pages but
>then reports a bug when the page frame number reaches 849513. This
>page frame should be in use since the count for the page instance is
>1. I do not know why sha_transform results in a page_fault(the data to
>be digested is the page which should be in memory). Would anyone give
>me some hints? Thanks.
>

Isn't this what KSM does? :) Check mm/ksm.c, it uses jhash2().

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