totalram is measured in pages, not bytes, so PAGE_SHIFT must be used when
trying to find 1/4096 of RAM.

Cc:  "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>