[PVE-User] memory question

[haoyun]

hello,everyone~
I have a cluster with 2 physical machines,and they are pve4.2
my physical machine:
root at cna5:~# free
             total       used       free     shared    buffers     cached
Mem:      65674780   21937328   43737452      93316     166488    1534868
-/+ buffers/cache:   20235972   45438808
Swap:      8388604          0    8388604


my vm:
root at debian:~# free
             total       used       free     shared    buffers     cached
Mem:       4063488     124792    3938696          0      10664      39144
-/+ buffers/cache:      74984    3988504
Swap:       901116          0     901116
root at debian:~# cd /dev/shm
root at debian:/dev/shm# dd if=/dev/zero of=dd.img bs=1M count=3000
dd: writing `dd.img': No space left on device
970+0 records in
969+0 records out
1016737792 bytes (1.0 GB) copied, 0.250504 s, 4.1 GB/s
root at debian:/dev/shm# free
             total       used       free     shared    buffers     cached
Mem:       4063488    1119324    2944164          0      10680    1032052
-/+ buffers/cache:      76592    3986896
Swap:       901116          0     901116


why?
who can help me?
thanks~