Since the page size may be different from an architecture/a system to
another it should not be hard coded to 4096.

As a consequence, several tests are failing on ppc64 due to a wrong page
size value.

This fix belongs to sysconf to get the current page size.
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Reviewed-by: Christopher Covington <cov@codeaurora.org>
Acked-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>