memcgroup: use vmalloc for mem_cgroup allocation

memcgroup: use vmalloc for mem_cgroup allocation

On ia64, this kmalloc() requires order-4 pages.  But this is not necessary to
be physically contiguous.  For big mem_cgroup, vmalloc is better.  For small
ones, kmalloc is used.

[[email protected]: simplification]
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Balbir Singh <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>