is_vmalloc_addr(): Check if an address is within the vmalloc boundaries

Checking if an address is a vmalloc address is done in a couple of places.
Define a common version in mm.h and replace the other checks.

Again the include structures suck.  The definition of VMALLOC_START and
VMALLOC_END is not available in vmalloc.h since highmem.c cannot be included
there.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index a49dd8d..0382c19 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -709,8 +709,7 @@
 mem_to_page(
 	void			*addr)
 {
-	if (((unsigned long)addr < VMALLOC_START) ||
-	    ((unsigned long)addr >= VMALLOC_END)) {
+	if ((!is_vmalloc_addr(addr))) {
 		return virt_to_page(addr);
 	} else {
 		return vmalloc_to_page(addr);