你好，专家们

我有一个mongodb服务器在我的2GB ec2实例上运行，使用以下命令

mongod-WiredTigerCacheSizeGb=0.5

下面是我的内存使用情况：

------------------------------------------------
MALLOC:      509658616 (  486.0 MiB) Bytes in use by application
MALLOC: +    100265984 (   95.6 MiB) Bytes in page heap freelist
MALLOC: +     10784344 (   10.3 MiB) Bytes in central cache freelist
MALLOC: +      8235328 (    7.9 MiB) Bytes in transfer cache freelist
MALLOC: +      3289712 (    3.1 MiB) Bytes in thread cache freelists
MALLOC: +      4063232 (    3.9 MiB) Bytes in malloc metadata
MALLOC:   ------------
MALLOC: =    636297216 (  606.8 MiB) Actual memory used (physical + swap)
MALLOC: +       385024 (    0.4 MiB) Bytes released to OS (aka unmapped)
MALLOC:   ------------
MALLOC: =    636682240 (  607.2 MiB) Virtual address space used
MALLOC:
MALLOC:          23555              Spans in use
MALLOC:             26              Thread heaps in use
MALLOC:           4096              Tcmalloc page size
------------------------------------------------

根据我的理解，使用的虚拟地址空间是MongoDB占用的总内存。如果有人能告诉我为什么它会超过0.5（500MB）的限制

----------------More  Info--------------------
{
    "name" : "wiredTiger",
    "supportsCommittedReads" : true,
    "oldestRequiredTimestampForCrashRecovery" : Timestamp(0, 0),
    "supportsPendingDrops" : true,
    "dropPendingIdents" : NumberLong(0),
    "supportsSnapshotReadConcern" : true,
    "readOnly" : false,
    "persistent" : true,
    "backupCursorOpen" : false
}

{
    "db" : "Database",
    "collections" : 43,
    "views" : 0,
    "objects" : 2780441,
    "avgObjSize" : 2756.87204116182,
    "dataSize" : 7665320055.0,
    "storageSize" : 2320449536.0,
    "numExtents" : 0,
    "indexes" : 58,
    "indexSize" : 156573696.0,
    "scaleFactor" : 1.0,
    "fsUsedSize" : 77780537344.0,
    "fsTotalSize" : 214746263552.0,
    "ok" : 1.0
}

内存消耗高于wiredtigercachesizeg中的设置值