Debian x64 limited to 4GB Memory- why?

Question

I have a virtual machine (running on a QNAP NAS) which is configured for 8GB of memory. But my Debian only uses 4GB of them. See outputs:

root@backuppc:/# lshw | grep "*-memory" -A 40
*-memory               
     description: System Memory
     physical id: 1000
     size: 8GiB

So the (virtual) hardware offers 8GB as you can see. But Debian does only use 4GB of them:

root@backuppc:/etc/grub.d# cat /proc/meminfo 
MemTotal:        3953672 kB
MemFree:          264084 kB
MemAvailable:    3300796 kB
Buffers:           24168 kB
Cached:          2833508 kB
SwapCached:         3724 kB
Active:          1749656 kB
Inactive:        1133408 kB
Active(anon):       5380 kB
Inactive(anon):    21856 kB
Active(file):    1744276 kB
Inactive(file):  1111552 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       1003516 kB
SwapFree:         970280 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:         22876 kB
Mapped:            29948 kB
Shmem:              1848 kB
KReclaimable:     576524 kB
Slab:             674656 kB
SReclaimable:     576524 kB
SUnreclaim:        98132 kB
KernelStack:        3200 kB
PageTables:         1904 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     2980352 kB
Committed_AS:     585300 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       16580 kB
VmallocChunk:          0 kB
Percpu:             2240 kB
HardwareCorrupted:     0 kB
AnonHugePages:      4096 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:      505700 kB
DirectMap2M:     7882752 kB
DirectMap1G:     2097152 kB

And yes, it is a 64bit system:

root@backuppc:/etc/grub.d# uname -a
Linux backuppc41 5.10.0-19-amd64 #1 SMP Debian 5.10.149-2 (2022-10-21) x86_64 GNU/Linux

And no, there are no kernel parameters limiting memory:

root@backuppc:/etc/grub.d# cat /proc/cmdline 
BOOT_IMAGE=/vmlinuz-5.10.0-19-amd64 root=/dev/mapper/backuppc--vg-root ro quiet zswap.enabled=1

Anyone having a clue why it uses only half of the memory?

Thanks for all hints!

/KNEBB

Answer 1

update shortly after posting.

This issue is solved: Looks like the "dynamically assigned memory" from the QNAP hypervisor has causedd this issue. Disabled dynamic memory and the Debian VM runs with 8GB fully.

Ok, I will investigate a little bit further if and how to use the dynamic memory feature.

/KNEBB