mm/zsmalloc: add per-class compact trace event

mm/zsmalloc: add per-class compact trace event

add per-class compact trace event to get number of migrated objects
and number of freed pages.

trace log is like below:

            bash-3863  [001] ....   141.791366: zs_compact_start: pool zram0
            bash-3863  [001] ....   141.791372: zs_compact: class 254: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791375: zs_compact: class 202: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791385: zs_compact: class 190: 1 objects migrated, 3 pages freed
            bash-3863  [001] ....   141.791393: zs_compact: class 168: 2 objects migrated, 2 pages freed
            bash-3863  [001] ....   141.791396: zs_compact: class 151: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791407: zs_compact: class 144: 5 objects migrated, 4 pages freed
            bash-3863  [001] ....   141.791427: zs_compact: class 126: 8 objects migrated, 8 pages freed
            bash-3863  [001] ....   141.791433: zs_compact: class 111: 1 objects migrated, 4 pages freed
            bash-3863  [001] ....   141.791459: zs_compact: class 107: 18 objects migrated, 12 pages freed
            bash-3863  [001] ....   141.791487: zs_compact: class 100: 18 objects migrated, 16 pages freed
            bash-3863  [001] ....   141.791509: zs_compact: class  94: 18 objects migrated, 9 pages freed
            bash-3863  [001] ....   141.791560: zs_compact: class  91: 44 objects migrated, 24 pages freed
            bash-3863  [001] ....   141.791605: zs_compact: class  83: 35 objects migrated, 20 pages freed
            bash-3863  [001] ....   141.791616: zs_compact: class  76: 8 objects migrated, 4 pages freed
            bash-3863  [001] ....   141.791644: zs_compact: class  74: 21 objects migrated, 9 pages freed
            bash-3863  [001] ....   141.791665: zs_compact: class  71: 18 objects migrated, 10 pages freed
            bash-3863  [001] ....   141.791736: zs_compact: class  67: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791763: zs_compact: class  66: 22 objects migrated, 8 pages freed
            bash-3863  [001] ....   141.791820: zs_compact: class  62: 18 objects migrated, 6 pages freed
            bash-3863  [001] ....   141.791826: zs_compact: class  58: 1 objects migrated, 4 pages freed
            bash-3863  [001] ....   141.791829: zs_compact: class  57: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791834: zs_compact: class  54: 2 objects migrated, 2 pages freed
...
            bash-3863  [001] ....   141.791952: zs_compact: class   4: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791964: zs_compact: class   3: 14 objects migrated, 1 pages freed
            bash-3863  [001] ....   141.791966: zs_compact: class   2: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791968: zs_compact: class   1: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791971: zs_compact: class   0: 0 objects migrated, 0 pages freed
            bash-3863  [001] ....   141.791973: zs_compact_end: pool zram0: 155 pages compacted

Also this patch changes trace_zsmalloc_compact_start[end] to
trace_zs_compact_start[end] to keep function naming consistent with others
in zsmalloc.

Link: http://lkml.kernel.org/r/1467882338-4300-8-git-send-email-opensource.ganesh@gmail.com
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>