Guest OS does not see all memory

[plastilin]

Hey. I noticed a strange one. Added 8 GB of RAM to the virtual machine. And inside she sees only 7.8 GB. What could be the problem? Virtual Machine is Ubuntu 16.04

Machine configuration

agent: 1
boot: c
bootdisk: scsi0
cores: 4
cpu: host
hotplug: disk,network,usb
machine: q35
memory: 8192
name: msschool
net0: virtio=D2:50:97:EB:86:B4,bridge=vmbr1,queues=2
numa: 1
ostype: l26
parent: Install_BBB
sata0: none,media=cdrom
scsi0: raid:vm-121-disk-0,cache=writeback,size=50G
scsihw: virtio-scsi-single
smbios1: uuid=d4ecd719-c7dd-4a1d-8c02-11daa663419b
sockets: 2
vmgenid: da393c41-f2d0-47cf-859c-584654cc5251

In VM

              total        used        free      shared  buff/cache   available
Mem:           7.8G        2.4G        4.2G         24M        1.2G        5.0G
Swap:          1.9G          0B        1.9G

 

[t.lamprecht]

Hi,

a little bit gets taken by the firmware and a little bit by the graphic adapter (IIRC), like my real system should have 64GiB, but adds up to a bit over 62 in free or /proc/meminfo

Check with dmidecode -t 16,17 if all virtual DIMMs are present and show the size you'd expect.

 

[plastilin]

Ok. Result is:

root@msschool:~# cat /proc/meminfo
MemTotal:        8174008 kB
MemFree:         2665916 kB
MemAvailable:    3061892 kB
Buffers:           17952 kB
Cached:           747312 kB
SwapCached:            0 kB
Active:          4866376 kB
Inactive:         411264 kB
Active(anon):    4524696 kB
Inactive(anon):   108456 kB
Active(file):     341680 kB
Inactive(file):   302808 kB
Unevictable:        3652 kB
Mlocked:            3652 kB
SwapTotal:       1951740 kB
SwapFree:        1951740 kB
Dirty:             11692 kB
Writeback:             0 kB
AnonPages:       4516196 kB
Mapped:           383148 kB
Shmem:            118236 kB
Slab:              99792 kB
SReclaimable:      45552 kB
SUnreclaim:        54240 kB
KernelStack:       31808 kB
PageTables:        35012 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     6038744 kB
Committed_AS:   14323628 kB
VmallocTotal:   34359738367 kB
VmallocUsed:           0 kB
VmallocChunk:          0 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:       94032 kB
DirectMap2M:     4100096 kB
DirectMap1G:     6291456 kB

# dmidecode 3.0
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.

Handle 0x1000, DMI type 16, 23 bytes
Physical Memory Array
        Location: Other
        Use: System Memory
        Error Correction Type: Multi-bit ECC
        Maximum Capacity: 8 GB
        Error Information Handle: Not Provided
        Number Of Devices: 1

Handle 0x1100, DMI type 17, 40 bytes
Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: Unknown
        Data Width: Unknown
        Size: 8192 MB
        Form Factor: DIMM
        Set: None
        Locator: DIMM 0
        Bank Locator: Not Specified
        Type: RAM
        Type Detail: Other
        Speed: Unknown
        Manufacturer: QEMU
        Serial Number: Not Specified
        Asset Tag: Not Specified
        Part Number: Not Specified
        Rank: Unknown
        Configured Clock Speed: Unknown
        Minimum Voltage: Unknown
        Maximum Voltage: Unknown
        Configured Voltage: Unknown