perf kmem: Add --live option for current allocation stat

perf kmem: Add --live option for current allocation stat

Currently 'perf kmem stat --page' shows total (page) allocation stat by
default, but sometimes one might want to see live (total alloc-only)
requests/pages only.  The new --live option does this by subtracting freed
allocation from the stat.

E.g.:

 # perf kmem stat --page

 SUMMARY (page allocator)
 ========================
 Total allocation requests     :          988,858   [        4,045,368 KB ]
 Total free requests           :          886,484   [        3,624,996 KB ]

 Total alloc+freed requests    :          885,969   [        3,622,628 KB ]
 Total alloc-only requests     :          102,889   [          422,740 KB ]
 Total free-only requests      :              515   [            2,368 KB ]

 Total allocation failures     :                0   [                0 KB ]

 Order     Unmovable   Reclaimable       Movable      Reserved  CMA/Isolated
 -----  ------------  ------------  ------------  ------------  ------------
     0       172,173         3,083       806,686             .             .
     1           284             .             .             .             .
     2         6,124            58             .             .             .
     3           114           335             .             .             .
     4             .             .             .             .             .
     5             .             .             .             .             .
     6             .             .             .             .             .
     7             .             .             .             .             .
     8             .             .             .             .             .
     9             .             .             1             .             .
    10             .             .             .             .             .
 # perf kmem stat --page --live

 SUMMARY (page allocator)
 ========================
 Total allocation requests     :          988,858   [        4,045,368 KB ]
 Total free requests           :          886,484   [        3,624,996 KB ]

 Total alloc+freed requests    :          885,969   [        3,622,628 KB ]
 Total alloc-only requests     :          102,889   [          422,740 KB ]
 Total free-only requests      :              515   [            2,368 KB ]

 Total allocation failures     :                0   [                0 KB ]

 Order     Unmovable   Reclaimable       Movable      Reserved  CMA/Isolated
 -----  ------------  ------------  ------------  ------------  ------------
     0         2,214         3,025        97,156             .             .
     1            59             .             .             .             .
     2            19            58             .             .             .
     3            23           335             .             .             .
     4             .             .             .             .             .
     5             .             .             .             .             .
     6             .             .             .             .             .
     7             .             .             .             .             .
     8             .             .             .             .             .
     9             .             .             .             .             .
    10             .             .             .             .             .
 #

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/1429592107-1807-4-git-send-email-namhyung@kernel.org
[ Added examples to the changeset log ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>