[IA64] - Make pfn_valid more precise for SGI Altix systems

A single SGI Altix system can be divided into multiple partitions,
each running their own instance of the Linux kernel.  pfn_valid()
is currently not optimal for any but the first partition, since it
does not compare the pfn with min_low_pfn before calling the more
costly ia64_pfn_valid().

Signed-off-by: Dean Roe <roe@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/arch/ia64/kernel/ia64_ksyms.c b/arch/ia64/kernel/ia64_ksyms.c
index 0157281..5db9d3b 100644
--- a/arch/ia64/kernel/ia64_ksyms.c
+++ b/arch/ia64/kernel/ia64_ksyms.c
@@ -42,6 +42,7 @@
 
 #ifdef CONFIG_VIRTUAL_MEM_MAP
 #include <linux/bootmem.h>
+EXPORT_SYMBOL(min_low_pfn);	/* defined by bootmem.c, but not exported by generic code */
 EXPORT_SYMBOL(max_low_pfn);	/* defined by bootmem.c, but not exported by generic code */
 #endif