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

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Message-ID: <alpine.DEB.2.00.1011181313140.26680@chino.kir.corp.google.com>
Date:	Thu, 18 Nov 2010 13:16:07 -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 Thu, 18 Nov 2010, Shaohui Zheng 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.
> 

You've modified the parser for mem= but not memmap= so the change needs 
additional support for the latter.

> > >  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.
> 

Your patchset doesn't do that, I'm talking specifically about the amount 
of memory left behind so that the kernel at least still boots.  That seems 
to be a function of e820_hide_mem() to do some sanity checking so we 
actually still get a kernel rather than the responsibility of the 
command-line parser.
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