linux-kernel - Re: [1/8,v3] NUMA Hotplug Emulator: add function to hide memory region via e820 table.

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Date:	Wed, 17 Nov 2010 00:16:34 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohui Zheng <shaohui.zheng@...el.com>
cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com,
	shaohui.zheng@...ux.intel.com, Yinghai Lu <yinghai@...nel.org>,
	Haicheng Li <haicheng.li@...el.com>
Subject: Re: [1/8,v3] NUMA Hotplug Emulator: add function to hide memory
 region via e820 table.

On Wed, 17 Nov 2010, shaohui.zheng@...el.com wrote:

> Index: linux-hpe4/arch/x86/kernel/e820.c
> ===================================================================
> --- linux-hpe4.orig/arch/x86/kernel/e820.c	2010-11-15 17:13:02.483461667 +0800
> +++ linux-hpe4/arch/x86/kernel/e820.c	2010-11-15 17:13:07.083461581 +0800
> @@ -971,6 +971,7 @@
>  }
>  
>  static int userdef __initdata;
> +static u64 max_mem_size __initdata = ULLONG_MAX;
>  
>  /* "mem=nopentium" disables the 4MB page tables. */
>  static int __init parse_memopt(char *p)
> @@ -989,12 +990,28 @@
>  
>  	userdef = 1;
>  	mem_size = memparse(p, &p);
> -	e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
> +	e820_remove_range(mem_size, max_mem_size - mem_size, E820_RAM, 1);
> +	max_mem_size = mem_size;
>  
>  	return 0;
>  }

This needs memmap= support as well, right?

>  early_param("mem", parse_memopt);
>  
> +#ifdef CONFIG_NODE_HOTPLUG_EMU
> +u64 __init e820_hide_mem(u64 mem_size)
> +{
> +	u64 start, end_pfn;
> +
> +	userdef = 1;
> +	end_pfn = e820_end_of_ram_pfn();
> +	start = (end_pfn << PAGE_SHIFT) - mem_size;
> +	e820_remove_range(start, max_mem_size - start, E820_RAM, 1);
> +	max_mem_size = start;
> +
> +	return start;
> +}
> +#endif

This doesn't have any sanity checking for whether e820_remove_range() will 
leave any significant amount of memory behind so the kernel will even boot 
(probably should have a guaranteed FAKE_NODE_MIN_SIZE left behind?).

> +
>  static int __init parse_memmap_opt(char *p)
>  {
>  	char *oldp;
--
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