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

From: Juergen Gross
Date: Thu Mar 19 2015 - 13:16:22 EST


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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