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SubjectRe: [PATCH] [RESEND] x86_64: add memory hotremove config option
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On Fri, 2008-09-05 at 19:44 +0200, Ingo Molnar wrote:
> * Gary Hade <garyhade@us.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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