mm: ksm: avoid trageted reclaim of ksm pages

Per Process Reclaim tries to avoid reclaiming of
shared pages by passing the target VMA. For anon and
file pages this works, but not for KSM. This is because
vma_address(page) will not return the intended value
resulting in crashes like this

[From 3.10 kernel]
kernel BUG at kernel/mm/rmap.c:534!
(vma_address+0x28/0x2c) from [<c01eff94>] (try_to_unmap_ksm+0x4c/0x170)
(try_to_unmap_ksm+0x4c/0x170) from [<c01e4834>] (try_to_unmap+0x34/0xa4)
(try_to_unmap+0x34/0xa4) from [<c01c8e64>] (shrink_page_list+0x3f0/0xa34)
(shrink_page_list+0x3f0/0xa34) from [<c01c9688>] (reclaim_pages_from_list)
(reclaim_pages_from_list+0xb0/0x100) from [<c0240ed0>] (reclaim_pte_range)
(reclaim_pte_range+0xf0/0x164) from [<c01e79a4>] (walk_page_range+0x1d0)
(walk_page_range+0x1d0/0x260) from [<c0241ccc>] (reclaim_task_anon+0xb0)
(reclaim_task_anon+0xb0/0x114) from [<c01f8d98>] (swap_fn+0x220/0x460)
(swap_fn+0x220/0x460) from [<c0133a38>] (process_one_work+0x294/0x430)
(process_one_work+0x294/0x430) from [<c0134720>] (worker_thread)
(worker_thread+0x224/0x358) from [<c01390d4>] (kthread+0xa0/0xac)
(kthread+0xa0/0xac) from [<c0105f38>] (ret_from_fork+0x14/0x3c)

Change-Id: I5208fb68372f7af72868e39399bf545fb7b774f3
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>