Re: [Xen-devel] [PATCH 1/2] xen: prepare p2m list for memory hotplug

[Juergen Gross <jgross@xxxxxxxx>]

On 03/19/2015 05:18 PM, David Vrabel wrote:
> On 19/03/15 14:31, Juergen Gross wrote:
> > Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
> > virtual mapped sparse p2m list") introduced a regression regarding to
> > memory hotplug for a pv-domain: as the virtual space for the p2m list
> > is allocated for the to be expected memory size of the domain only,
> > hotplugged memory above that size will not be usable by the domain.
> >
> > Correct this by using a configurable size for the p2m list in case of
> > memory hotplug enabled (default supported memory size is 512 GB for
> > 64 bit domains and 4 GB for 32 bit domains).
> [...]
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -91,6 +91,17 @@ EXPORT_SYMBOL_GPL(xen_p2m_size);
> >   unsigned long xen_max_p2m_pfn __read_mostly;
> >   EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);
> >
> > +#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> > +#ifdef CONFIG_X86_32
> > +BUILD_BUG_ON_MSG(CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT > 64)
> > +#endif
> > +#define P2M_LIMIT max(xen_max_p2m_pfn,                                 \
> > +       ((unsigned long)((u64)CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT * \
> > +       1024 * 1024 * 1024 / PAGE_SIZE)))
> > +#else
> > +#define P2M_LIMIT xen_max_p2m_pfn
> > +#endif
> Can you arrange the #ifdef's to set xen_max_p2m_pfn to the right value
> instead of introducing P2M_LIMIT?
Hmm, this would require additional checks in setup.c. What about:

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
#define P2M_LIMIT CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
#else
#define P2M_LIMIT 0
#endif

and do the max(...) calculation in xen_vmalloc_p2m_tree()?


Juergen


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