2G⇒4Gのメモリ増設を行ったのですが。

# cat /proc/meminfo
MemTotal: 3339880 kB
MemFree: 2952072 kB
Buffers: 14972 kB
Cached: 154316 kB
SwapCached: 0 kB
Active: 219836 kB
Inactive: 107852 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 3339880 kB
LowFree: 2952072 kB
SwapTotal: 8385920 kB
SwapFree: 8385920 kB
Dirty: 200 kB
Writeback: 0 kB
Mapped: 190860 kB
Slab: 30196 kB
Committed_AS: 297492 kB
PageTables: 8648 kB
VmallocTotal: 536870911 kB
VmallocUsed: 267064 kB
VmallocChunk: 536603631 kB
HugePages_Total: 0
HugePages_Free: 0
Hugepagesize: 2048 kB

4G全てを認識していないようなのですが、何が原因だと思われますか？