selftest: add a testcase of ksm zero pages

Add a function test_unmerge_zero_page() to test the functionality on
unsharing and counting ksm-placed zero pages and counting of this patch
series.

test_unmerge_zero_page() actually contains four subjct test objects:
(1) whether the count of ksm zero pages can update correctly after merging;
(2) whether the count of ksm zero pages can update correctly after
    unmerging by madvise(...MADV_UNMERGEABLE);
(3) whether the count of ksm zero pages can update correctly after
	unmerging by triggering write fault.
(4) whether ksm zero pages are really unmerged.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: xu xin <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Xiaokai Ran <[email protected]>
Reviewed-by: Yang Yang <[email protected]>
Cc: Claudio Imbrenda <[email protected]>
Cc: Xuexin Jiang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions