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Date: Sat, 19 Feb 2011 20:03:41 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: Yinghai Lu <yinghai@kernel.org>
cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@zytor.com>, Tejun Heo <tj@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [PATCH 2/4] x86, numa: Do not adjust start/end for
 early_node_mem()
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References: <4D5EC05A.60103@kernel.org> <4D5EC184.6000505@kernel.org>
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On Fri, 18 Feb 2011, Yinghai Lu wrote:

> Index: linux-2.6/arch/x86/mm/numa_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/numa_64.c
> +++ linux-2.6/arch/x86/mm/numa_64.c
> @@ -164,14 +164,9 @@ static void * __init early_node_mem(int
>  	unsigned long mem;
>  
>  	/*
> -	 * put it on high as possible
> -	 * something will go with NODE_DATA
> +	 * memblock find will follow top-down, so don't need to adjust
> +	 *   start anymore
>  	 */
> -	if (start < (MAX_DMA_PFN<<PAGE_SHIFT))
> -		start = MAX_DMA_PFN<<PAGE_SHIFT;
> -	if (start < (MAX_DMA32_PFN<<PAGE_SHIFT) &&
> -	    end > (MAX_DMA32_PFN<<PAGE_SHIFT))
> -		start = MAX_DMA32_PFN<<PAGE_SHIFT;
>  	mem = memblock_x86_find_in_range_node(nodeid, start, end, size, align);
>  	if (mem != MEMBLOCK_ERROR)
>  		return __va(mem);
> 

The old code guarantees that the range is from a single zone, and even 
though memblock may be top -> down, it seems like there would be 
configurations where this would still be an issue (perhaps simulating it 
with numa=fake for testing?) if it crosses the boundary.