linux-kernel - Re: [PATCH] [RESEND] x86_64: add memory hotremove config option

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Message-Id: <1220638478.25932.20.camel@badari-desktop>
Date:	Fri, 05 Sep 2008 11:14:38 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Gary Hade <garyhade@...ibm.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Chris McDermott <lcm@...ibm.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] [RESEND] x86_64: add memory hotremove config option


On Fri, 2008-09-05 at 19:44 +0200, Ingo Molnar wrote:
> * Gary Hade <garyhade@...ibm.com> wrote:
> 
> > Add memory hotremove config option to x86_64
> > 
> > Memory hotremove functionality can currently be configured into the 
> > ia64, powerpc, and s390 kernels.  This patch makes it possible to 
> > configure the memory hotremove functionality into the x86_64 kernel as 
> > well.
> 
> hm, why is it for 64-bit only?
> 
> > +++ linux-2.6.27-rc5/arch/x86/Kconfig	2008-09-03 13:34:55.000000000 -0700
> > @@ -1384,6 +1384,9 @@
> >  	def_bool y
> >  	depends on X86_64 || (X86_32 && HIGHMEM)
> > 
> > +config ARCH_ENABLE_MEMORY_HOTREMOVE
> > +	def_bool y
> 
> so this will break the build on 32-bit, if CONFIG_MEMORY_HOTREMOVE=y? 
> mm/memory_hotplug.c assumes that remove_memory() is provided by the 
> architecture.
> 
> > +#ifdef CONFIG_MEMORY_HOTREMOVE
> > +int remove_memory(u64 start, u64 size)
> > +{
> > +	unsigned long start_pfn, end_pfn;
> > +	unsigned long timeout = 120 * HZ;
> > +	int ret;
> > +	start_pfn = start >> PAGE_SHIFT;
> > +	end_pfn = start_pfn + (size >> PAGE_SHIFT);
> > +	ret = offline_pages(start_pfn, end_pfn, timeout);
> > +	if (ret)
> > +		goto out;
> > +	/* Arch-specific calls go here */
> > +out:
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(remove_memory);
> > +#endif /* CONFIG_MEMORY_HOTREMOVE */
> 
> hm, nothing appears to be arch-specific about this trivial wrapper 
> around offline_pages().

Yes. All the archs (ppc64, ia64, s390, x86_64) have exact same
function. No architecture needed special handling so far (initial
versions of ppc64 needed extra handling, but I moved the code
to different place). 

We can make this generic and kill all arch-specific ones.
Initially, we didn't know if any arch needs special handling -
so ended up having private functions for each arch.  
I think its time to merge them all.

> 
> Shouldnt this be moved to the CONFIG_MEMORY_HOTREMOVE portion of 
> mm/memory_hotplug.c instead, as a weak function? That way architectures 
> only have to enable ARCH_ENABLE_MEMORY_HOTREMOVE - and architectures 
> with different/special needs can override it.

Yes. We should do that. I will send out a patch.

Thanks,
Badari

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