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

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Date:	Thu, 18 Nov 2010 17:20:52 +0800
From:	Shaohui Zheng <shaohui.zheng@...el.com>
To:	David Rientjes <rientjes@...gle.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, Nov 17, 2010 at 12:16:34AM -0800, David Rientjes wrote:
> 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?
we did not do the testing after combine both memmap and numa=hide paramter, 
I think that the result should similar with mem=XX, they both remove a memory
region from the e820 table.

> 
> >  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?).

it should not be checked here, it should be checked by the function who call
 e820_hide_mem, and truncate the mem_size with FAKE_NODE_MIN_SIZE.

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

-- 
Thanks & Regards,
Shaohui

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