我注意到free -h我的 Mint Linux 19.3 机器上报告有 13G 的内存可用。但是，应该有 16GB 的内存可用。我尝试了各种测试这里根据以下显示的结果，尝试解释差异但无法弄清楚，有人可以解释吗？
thinkpad:~$ sudo dmidecode -t memory
# dmidecode 3.1
Getting SMBIOS data from sysfs.
SMBIOS 3.1.1 present.
Handle 0x0001, DMI type 16, 23 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 64 GB
Error Information Handle: 0x0000
Number Of Devices: 2
Handle 0x0008, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0001
Error Information Handle: 0x0007
Total Width: 64 bits
Data Width: 64 bits
Size: 16384 MB
Form Factor: SODIMM
Set: None
Locator: DIMM 0
Bank Locator: P0 CHANNEL A
Type: DDR4
Type Detail: Synchronous Unbuffered (Unregistered)
Speed: 2400 MT/s
Manufacturer: Samsung
Serial Number: 344662CE
Asset Tag: Not Specified
Part Number: M471A2K43DB1-CTD
Rank: 2
Configured Clock Speed: 2400 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
Handle 0x000B, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x0001
Error Information Handle: 0x000A
Total Width: Unknown
Data Width: Unknown
Size: No Module Installed
Form Factor: Unknown
Set: None
Locator: DIMM 0
Bank Locator: P0 CHANNEL B
Type: Unknown
Type Detail: Unknown
Speed: Unknown
Manufacturer: Unknown
Serial Number: Unknown
Asset Tag: Not Specified
Part Number: Unknown
Rank: Unknown
Configured Clock Speed: Unknown
Minimum Voltage: Unknown
Maximum Voltage: Unknown
Configured Voltage: Unknown
thinkpad:~$ cat /proc/meminfo | grep Slab
Slab: 618032 kB
thinkpad:~$
thinkpad:~$ dmesg | grep stolen
thinkpad:~$ dmesg | grep e820
[ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009efff] usable
[ 0.000000] BIOS-e820: [mem 0x000000000009f000-0x000000000009ffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000009bfffff] usable
[ 0.000000] BIOS-e820: [mem 0x0000000009c00000-0x0000000009d80fff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000009d81000-0x0000000009efffff] usable
[ 0.000000] BIOS-e820: [mem 0x0000000009f00000-0x0000000009f0afff] ACPI NVS
[ 0.000000] BIOS-e820: [mem 0x0000000009f0b000-0x00000000b85a8fff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000b85a9000-0x00000000bbd7dfff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000bbd7e000-0x00000000bdd7dfff] ACPI NVS
[ 0.000000] BIOS-e820: [mem 0x00000000bdd7e000-0x00000000bddfdfff] ACPI data
[ 0.000000] BIOS-e820: [mem 0x00000000bddfe000-0x00000000beffffff] usable
[ 0.000000] BIOS-e820: [mem 0x00000000bf000000-0x00000000bfffffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fd200000-0x00000000fd2fffff] reserved
[ 0.000000] BIOS-e820: [mem 0x00000000fed80000-0x00000000fed80fff] reserved
[ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x00000003beffffff] usable
[ 0.000000] e820: update [mem 0xb3d60018-0xb3d6e057] usable ==> usable
[ 0.000000] e820: update [mem 0xb3d60018-0xb3d6e057] usable ==> usable
[ 0.000000] e820: update [mem 0xb3d52018-0xb3d5f457] usable ==> usable
[ 0.000000] e820: update [mem 0xb3d52018-0xb3d5f457] usable ==> usable
[ 0.000019] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[ 0.000020] e820: remove [mem 0x000a0000-0x000fffff] usable
[ 0.057910] e820: update [mem 0xb545f000-0xb54effff] usable ==> reserved
[ 0.513068] e820: reserve RAM buffer [mem 0x0009f000-0x0009ffff]
[ 0.513069] e820: reserve RAM buffer [mem 0x09c00000-0x0bffffff]
[ 0.513070] e820: reserve RAM buffer [mem 0x09f00000-0x0bffffff]
[ 0.513070] e820: reserve RAM buffer [mem 0xb3d52018-0xb3ffffff]
[ 0.513071] e820: reserve RAM buffer [mem 0xb3d60018-0xb3ffffff]
[ 0.513071] e820: reserve RAM buffer [mem 0xb545f000-0xb7ffffff]
[ 0.513072] e820: reserve RAM buffer [mem 0xb85a9000-0xbbffffff]
[ 0.513072] e820: reserve RAM buffer [mem 0xbf000000-0xbfffffff]
[ 0.513073] e820: reserve RAM buffer [mem 0x3bf000000-0x3bfffffff]
thinkpad:~$ free -h
total used free shared buff/cache available
Mem: 13G 2.6G 7.0G 172M 4.0G 10G
Swap: 2.0G 0B 2.0G