add_to_kill() expects the first 'tk' to be pre-allocated, it makes
subsequent allocations on need basis, this makes the code a bit
difficult to read.

Move all the allocation internal to add_to_kill() and drop the **tk
argument.

Link: http://lkml.kernel.org/r/1565112345-28754-2-git-send-email-jane.chu@oracle.comSigned-off-by: NJane Chu <jane.chu@oracle.com>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>