linux-kernel - Re: [PATCH] x86: only clear node

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Date:	Fri, 26 Jun 2009 13:54:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	cl@...ux-foundation.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, ntl@...ox.com, mel@....ul.ie,
	suresh.b.siddha@...el.com, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, rusty@...tcorp.com.au, steiner@....com,
	rientjes@...gle.com, containers@...ts.linux-foundation.org
Subject: Re: [PATCH] x86: only clear node_states for 64bit

On Mon, 22 Jun 2009 08:38:50 -0700
Yinghai Lu <yinghai@...nel.org> wrote:

> Nathan reported that
> | commit 73d60b7f747176dbdff826c4127d22e1fd3f9f74
> | Author: Yinghai Lu <yinghai@...nel.org>
> | Date:   Tue Jun 16 15:33:00 2009 -0700
> |
> |    page-allocator: clear N_HIGH_MEMORY map before we set it again
> |    
> |    SRAT tables may contains nodes of very small size.  The arch code may
> |    decide to not activate such a node.  However, currently the early boot
> |    code sets N_HIGH_MEMORY for such nodes.  These nodes therefore seem to be
> |    active although these nodes have no present pages.
> |    
> |    For 64bit N_HIGH_MEMORY == N_NORMAL_MEMORY, so that works for 64 bit too
> 
> the cpuset.mems cgroup attribute on an i386 kvm guest
> 
> fix it by only clearing node_states[N_NORMAL_MEMORY] for 64bit only.
> and need to do save/restore for that in find_zone_movable_pfn
> 

There appear to be some words omitted from this changelog - it doesn't
make sense.

I think that perhaps a line got deleted before "the cpuset.mems cgroup
...".  That was the line which actualy describes the bug which we're
fixing.  Or perhaps it was a single word?  "zeroes".

I did this:

Nathan reported that
: 
: | commit 73d60b7f747176dbdff826c4127d22e1fd3f9f74
: | Author: Yinghai Lu <yinghai@...nel.org>
: | Date:   Tue Jun 16 15:33:00 2009 -0700
: |
: |    page-allocator: clear N_HIGH_MEMORY map before we set it again
: |
: |    SRAT tables may contains nodes of very small size.  The arch code may
: |    decide to not activate such a node.  However, currently the early boot
: |    code sets N_HIGH_MEMORY for such nodes.  These nodes therefore seem to be
: |    active although these nodes have no present pages.
: |
: |    For 64bit N_HIGH_MEMORY == N_NORMAL_MEMORY, so that works for 64 bit too
: 
: unintentionally and incorrectly clears the cpuset.mems cgroup attribute on
: an i386 kvm guest
: 
: Fix this by only clearing node_states[N_NORMAL_MEMORY] for 64bit only. 
: and need to do save/restore for that in find_zone_movable_pfn

Please check whether that is correct.  If not, how should it be changed?

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