hi,
version: WiredTiger version :3.2.12
cache-size: --wiredTigerCacheSizeGB 12
data-size: Just have 1.3G
The following is mongostat result,

insert query update delete getmore command % dirty % used flushes vsize   res qr|qw ar|aw netIn netOut conn       set repl                      time
    *0    *0     *0     *0       0     3|0     0.0   22.4       0 3.56G 1.49G   0|0   0|0  427b  22.8k    3 spam_view  SEC 2017-07-04T11:35:12+08:00

PID=5668 - Swap used : 1.24G - (mongod )

The issue:
Mongd process use 1.2G SWAP, why mongod use so much swap while wiredTigerCacheSizeGB is enough and data path only 1.3G.