Message-ID: <4A4538FE.2090101@kernel.org>
Date: Fri, 26 Jun 2009 14:09:18 -0700
From: Yinghai Lu <yinghai@kernel.org>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: cl@linux-foundation.org, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com,
       ntl@pobox.com, mel@csn.ul.ie, suresh.b.siddha@intel.com,
       linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
       rusty@rustcorp.com.au, steiner@sgi.com, rientjes@google.com,
       containers@lists.linux-foundation.org
Subject: Re: [PATCH] x86: only clear node_states for 64bit
References: <4A05269D.8000701@kernel.org>	<20090512111623.GG25923@csn.ul.ie>	<4A0A64FB.4080504@kernel.org>	<20090513145950.GB28097@csn.ul.ie>	<4A0C4910.7090508@kernel.org>	<4A0C4A2A.6080009@kernel.org>	<20090514095414.ba8356e5.akpm@linux-foundation.org>	<4A0C4F67.5080802@kernel.org>	<20090514102554.b3a36f19.akpm@linux-foundation.org>	<4A0C563A.3020100@kernel.org>	<4A2758CB.9090404@kernel.org>	<alpine.DEB.1.10.0906041236520.5377@gentwo.org>	<4A27FAD4.2010104@kernel.org>	<alpine.DEB.1.10.0906041309230.8080@gentwo.org>	<4A2803D1.4070001@kernel.org>	<m3bpokiv0u.fsf@pobox.com>	<4A3B49BA.40100@kernel.org>	<m3prd0havh.fsf@pobox.com>	<4A3D7419.8040305@kernel.org>	<m3my807ug3.fsf@pobox.com>	<4A3FA58A.3010909@kernel.org> <20090626135428.d8f88a70.akpm@linux-foundation.org>
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Andrew Morton wrote:
> On Mon, 22 Jun 2009 08:38:50 -0700
> Yinghai Lu <yinghai@kernel.org> wrote:
> 
>> Nathan reported that
>> | commit 73d60b7f747176dbdff826c4127d22e1fd3f9f74
>> | Author: Yinghai Lu <yinghai@kernel.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@kernel.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
"
==> 

32bit assume NORMAL_MEMORY bit and HIGH_MEMORY bit are set for Node0 always.

and some code only check if HIGH_MEMORY is there to know if NORMAL_MEMORY is there.

YH

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