[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>

arch/ia64/kernel/ia64_ksyms.c

@@ -42,6 +42,7 @@ EXPORT_SYMBOL(clear_page);
 
 #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
 

include/asm-ia64/page.h

@@ -110,8 +110,9 @@ extern int ia64_pfn_valid (unsigned long pfn);
 # define pfn_to_page(pfn)	(mem_map + (pfn))
 #elif defined(CONFIG_DISCONTIGMEM)
 extern struct page *vmem_map;
+extern unsigned long min_low_pfn;
 extern unsigned long max_low_pfn;
-# define pfn_valid(pfn)		(((pfn) < max_low_pfn) && ia64_pfn_valid(pfn))
+# define pfn_valid(pfn)		(((pfn) >= min_low_pfn) && ((pfn) < max_low_pfn) && ia64_pfn_valid(pfn))
 # define page_to_pfn(page)	((unsigned long) (page - vmem_map))
 # define pfn_to_page(pfn)	(vmem_map + (pfn))
 #endif