I'm running my new computer which has 8GB of RAM installed, which is visable from BIOS page, does not show in /proc/meminfo

uname -a
Linux localhost 3.0.6-gentoo #2 SMP PREEMPT Sat Nov 19 10:45:22 GMT-- x86_64 AMD   
Phenom(tm) II X4 955 Processor AuthenticAMD GNU/Linux

The result of /proc/meminfo is as follows: (thans Andrey)

MemTotal:        4021348 kB
MemFree:         1440280 kB
Buffers:           23696 kB
Cached:          1710828 kB
SwapCached:         4956 kB
Active:          1389904 kB
Inactive:         841364 kB
Active(anon):    1337812 kB
Inactive(anon):   714060 kB
Active(file):      52092 kB
Inactive(file):   127304 kB
Unevictable:          32 kB
Mlocked:              32 kB
SwapTotal:       8388604 kB
SwapFree:        8047900 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:        492732 kB
Mapped:            47528 kB
Shmem:           1555120 kB
Slab:             267724 kB
SReclaimable:     177464 kB
SUnreclaim:        90260 kB
KernelStack:        1176 kB
PageTables:        12148 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    10399276 kB
Committed_AS:    3293896 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      317008 kB
VmallocChunk:   34359398908 kB
AnonHugePages:    120832 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       23552 kB
DirectMap2M:     3088384 kB
DirectMap1G:     1048576 kB

I have tried using mem=8G as a kernel boot parameter, I read a post about setting HIGHMEM64G to yes, before realising that only applies to 32bit kernels.

Trying dmindecode -t memory

SMBIOS 2.7 present.

Handle 0x0026, DMI type 16, 23 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: Multi-bit ECC
    Maximum Capacity: 32 GB
    Error Information Handle: Not Provided
    Number Of Devices: 4

Handle 0x0028, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0026
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM0
    Bank Locator: BANK0
    Type: <OUT OF SPEC>
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Manufacturer0
    Serial Number: SerNum0
    Asset Tag: AssetTagNum0
    Part Number: Array1_PartNumber0
    Rank: Unknown

Handle 0x002A, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0026
    Error Information Handle: Not Provided
    Total Width: Unknown
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: DIMM1
    Bank Locator: BANK1
    Type: Unknown
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer: Manufacturer1
    Serial Number: SerNum1
    Asset Tag: AssetTagNum1
    Part Number: Array1_PartNumber1
    Rank: Unknown

Handle 0x002C, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0026
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM2
    Bank Locator: BANK2
    Type: <OUT OF SPEC>
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Manufacturer2
    Serial Number: SerNum2
    Asset Tag: AssetTagNum2
    Part Number: Array1_PartNumber2
    Rank: Unknown

Handle 0x002E, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0026
    Error Information Handle: Not Provided
    Total Width: Unknown
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: DIMM3
    Bank Locator: BANK3
    Type: Unknown
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer: Manufacturer3
    Serial Number: SerNum3
    Asset Tag: AssetTagNum3
    Part Number: Array1_PartNumber3
    Rank: Unknown