Where's my memory going on ?

The free command shows I used a lot of memory
free -m
             total used free shared buffers cached
Mem: 63800 62821 978 0 48 2794
-/+ buffers/cache: 59979 3821
Swap: 22989 3270 19719

----------------------------------------------------------
but I use ps_mem.py (https://raw.github.com/pixelb/ps_mem/master/ps_mem.py) to count my app used memory

  2.4 GiB + 2.8 MiB = 2.4 GiB java
---------------------------------
                          2.5 GiB
=================================

root@ubuntu:/tmp# df -h|grep shm
none 32G 0 32G 0% /run/shm

shm used 32G ,app used 2.5G ,slab used 6.5G.
I have no HugePages.
I run 'sync&&echo 3 > /proc/sys/vm/drop_caches'. It doesn't look like I have a huge cache.

So,where's my memory going on ?

My os version:
root@ubuntu:/tmp# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04
Codename: precise
root@ubuntu:/tmp# uname -r
3.2.0-93-generic

-----------------------------------------------------------
cat /proc/meminfo
MemTotal: 65331452 kB
MemFree: 696240 kB
Buffers: 49860 kB
Cached: 3157536 kB
SwapCached: 358948 kB
Active: 2947712 kB
Inactive: 4528344 kB
Active(anon): 2398892 kB
Inactive(anon): 440084 kB
Active(file): 548820 kB
Inactive(file): 4088260 kB
Unevictable: 0 kB
Mlocked: 0 kB
SwapTotal: 23541752 kB
SwapFree: 20197284 kB
Dirty: 111812 kB
Writeback: 0 kB
AnonPages: 2562660 kB
Mapped: 18768 kB
Shmem: 1540 kB
Slab: 6545040 kB
SReclaimable: 240500 kB
SUnreclaim: 6304540 kB
KernelStack: 3368 kB
PageTables: 25056 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 56207476 kB
Committed_AS: 6508200 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 391884 kB
VmallocChunk: 34325260484 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 94208 kB
DirectMap2M: 12414976 kB
DirectMap1G: 54525952 kB