我曾经有两个内存条，每个 8GB。我把其中一根换成了 16G 内存条，原以为现在总共有 24GB，但实际只有 20GB。 free -h 的结果：
total used free shared buff/cache available
Mem: 19Gi 2.8Gi 12Gi 105Mi 3.9Gi 16Gi
Swap: 2.0Gi 0B 2.0Gi
猫 /proc/meminfo
MemTotal: 20292048 kB
MemFree: 13254056 kB
MemAvailable: 16923208 kB
Buffers: 269448 kB
Cached: 3706108 kB
SwapCached: 0 kB
Active: 1319968 kB
Inactive: 4874796 kB
Active(anon): 14752 kB
Inactive(anon): 2312796 kB
Active(file): 1305216 kB
Inactive(file): 2562000 kB
Unevictable: 132 kB
Mlocked: 132 kB
SwapTotal: 2097148 kB
SwapFree: 2097148 kB
Dirty: 524 kB
Writeback: 0 kB
AnonPages: 2219512 kB
Mapped: 1341800 kB
Shmem: 108248 kB
KReclaimable: 159592 kB
Slab: 372516 kB
SReclaimable: 159592 kB
SUnreclaim: 212924 kB
KernelStack: 23104 kB
PageTables: 56624 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 12243172 kB
Committed_AS: 13539940 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 67940 kB
VmallocChunk: 0 kB
Percpu: 25088 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 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: 635844 kB
DirectMap2M: 10717184 kB
sudo dmidecode -t 内存
Getting SMBIOS data from sysfs.
SMBIOS 3.3.0 present.
# SMBIOS implementations newer than version 3.2.0 are not
# fully supported by this version of dmidecode.
Handle 0x0022, 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: 0x0025
Number Of Devices: 2
Handle 0x0023, DMI type 17, 92 bytes
Memory Device
Array Handle: 0x0022
Error Information Handle: 0x0026
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: 3200 MT/s
Manufacturer: Unknown
Serial Number: E81F0ECB
Asset Tag: Not Specified
Part Number: CT16G4SFRA32A.M16FR
Rank: 2
Configured Memory Speed: 3200 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
Memory Technology: DRAM
Memory Operating Mode Capability: Volatile memory
Firmware Version: Unknown
Module Manufacturer ID: Bank 6, Hex 0x9B
Module Product ID: Unknown
Memory Subsystem Controller Manufacturer ID: Unknown
Memory Subsystem Controller Product ID: Unknown
Non-Volatile Size: None
Volatile Size: 16 GB
Cache Size: None
Logical Size: None
Handle 0x0024, DMI type 17, 92 bytes
Memory Device
Array Handle: 0x0022
Error Information Handle: 0x0027
Total Width: 64 bits
Data Width: 64 bits
Size: 8192 MB
Form Factor: SODIMM
Set: None
Locator: DIMM 0
Bank Locator: P0 CHANNEL B
Type: DDR4
Type Detail: Synchronous Unbuffered (Unregistered)
Speed: 3200 MT/s
Manufacturer: Samsung
Serial Number: 00000000
Asset Tag: Not Specified
Part Number: M471A1G44AB0-CWE
Rank: 1
Configured Memory Speed: 3200 MT/s
Minimum Voltage: 1.2 V
Maximum Voltage: 1.2 V
Configured Voltage: 1.2 V
Memory Technology: DRAM
Memory Operating Mode Capability: Volatile memory
Firmware Version: Unknown
Module Manufacturer ID: Bank 1, Hex 0xCE
Module Product ID: Unknown
Memory Subsystem Controller Manufacturer ID: Unknown
Memory Subsystem Controller Product ID: Unknown
Non-Volatile Size: None
Volatile Size: 8 GB
Cache Size: None
Logical Size: None
Linux：Ubuntu 20.04.6 LTS
我可以采取什么措施来查看我的所有 RAM 还是这是硬件问题？
UPD Journalctl -b0 -k 日志：
BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009efff] usable
BIOS-e820: [mem 0x000000000009f000-0x00000000000bffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x0000000009efffff] usable
BIOS-e820: [mem 0x0000000009f00000-0x0000000009f0efff] ACPI NVS
BIOS-e820: [mem 0x0000000009f0f000-0x00000000b89e8fff] usable
BIOS-e820: [mem 0x00000000b89e9000-0x00000000babe8fff] reserved
BIOS-e820: [mem 0x00000000babe9000-0x00000000c8dfefff] usable
BIOS-e820: [mem 0x00000000c8dff000-0x00000000cbdfefff] reserved
BIOS-e820: [mem 0x00000000cbdff000-0x00000000cdf7efff] ACPI NVS
BIOS-e820: [mem 0x00000000cdf7f000-0x00000000cdffefff] ACPI data
BIOS-e820: [mem 0x00000000cdfff000-0x00000000cdffffff] usable
BIOS-e820: [mem 0x00000000ce000000-0x00000000cfffffff] reserved
BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
BIOS-e820: [mem 0x00000000fdc00000-0x00000000fdcfffff] reserved
BIOS-e820: [mem 0x00000000fe000000-0x00000000fe0fffff] reserved
BIOS-e820: [mem 0x00000000fec00000-0x00000000fec01fff] reserved
BIOS-e820: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
BIOS-e820: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
BIOS-e820: [mem 0x00000000fed80000-0x00000000fed81fff] reserved
BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
BIOS-e820: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
BIOS-e820: [mem 0x0000000100000000-0x000000052e2fffff] usable
BIOS-e820: [mem 0x000000052e300000-0x000000062fffffff] reserved
extended physical RAM map:
reserve setup_data: [mem 0x0000000000000000-0x000000000009efff] usable
reserve setup_data: [mem 0x000000000009f000-0x00000000000bffff] reserved
reserve setup_data: [mem 0x0000000000100000-0x0000000009efffff] usable
reserve setup_data: [mem 0x0000000009f00000-0x0000000009f0efff] ACPI NVS
reserve setup_data: [mem 0x0000000009f0f000-0x00000000adb86017] usable
reserve setup_data: [mem 0x00000000adb86018-0x00000000adb93857] usable
reserve setup_data: [mem 0x00000000adb93858-0x00000000b2f69017] usable
reserve setup_data: [mem 0x00000000b2f69018-0x00000000b2f77057] usable
reserve setup_data: [mem 0x00000000b2f77058-0x00000000b89e8fff] usable
reserve setup_data: [mem 0x00000000b89e9000-0x00000000babe8fff] reserved
reserve setup_data: [mem 0x00000000babe9000-0x00000000c8dfefff] usable
reserve setup_data: [mem 0x00000000c8dff000-0x00000000cbdfefff] reserved
reserve setup_data: [mem 0x00000000cbdff000-0x00000000cdf7efff] ACPI NVS
reserve setup_data: [mem 0x00000000cdf7f000-0x00000000cdffefff] ACPI data
reserve setup_data: [mem 0x00000000cdfff000-0x00000000cdffffff] usable
reserve setup_data: [mem 0x00000000ce000000-0x00000000cfffffff] reserved
reserve setup_data: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
reserve setup_data: [mem 0x00000000fdc00000-0x00000000fdcfffff] reserved
reserve setup_data: [mem 0x00000000fe000000-0x00000000fe0fffff] reserved
reserve setup_data: [mem 0x00000000fec00000-0x00000000fec01fff] reserved
reserve setup_data: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
reserve setup_data: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
reserve setup_data: [mem 0x00000000fed80000-0x00000000fed81fff] reserved
reserve setup_data: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
reserve setup_data: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
reserve setup_data: [mem 0x0000000100000000-0x000000052e2fffff] usable
reserve setup_data: [mem 0x000000052e300000-0x000000062fffffff] reserved
e820: reserve RAM buffer [mem 0x0009f000-0x0009ffff]
e820: reserve RAM buffer [mem 0x09f00000-0x0bffffff]
e820: reserve RAM buffer [mem 0xadb86018-0xafffffff]
e820: reserve RAM buffer [mem 0xb2f69018-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb321f000-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb3351000-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb89e9000-0xbbffffff]
e820: reserve RAM buffer [mem 0xc8dff000-0xcbffffff]
e820: reserve RAM buffer [mem 0xce000000-0xcfffffff]
e820: reserve RAM buffer [mem 0x52e300000-0x52fffffff]
[drm] vm size is 262144 GB, 4 levels, block size is 9-bit, fragment size is 9-bit
amdgpu 0000:05:00.0: amdgpu: VRAM: 4096M 0x000000F400000000 - 0x000000F4FFFFFFFF (4096M used)
amdgpu 0000:05:00.0: amdgpu: GART: 1024M 0x0000000000000000 - 0x000000003FFFFFFF
amdgpu 0000:05:00.0: amdgpu: AGP: 267419648M 0x000000F800000000 - 0x0000FFFFFFFFFFFF
[drm] Detected VRAM RAM=4096M, BAR=4096M
[drm] RAM width 128bits DDR4
[drm] amdgpu: 4096M of VRAM memory ready
[drm] amdgpu: 4096M of GTT memory ready.
[drm] GART: num cpu pages 262144, num gpu pages 262144
[drm] PCIE GART of 1024M enabled.
[drm] PTB located at 0x000000F400900000
答案1
根据您发布的日志和描述的行为，我相信您的 AMD Ryzen 7 5700U 也是集成显卡，没有自己的 RAM。
您的 BIOS 中可能有一个选项可以调整集成显卡 VRAM，这将从您安装的系统 RAM 中占用 RAM。
您的日志当前显示 4096M 已分配给您的集成显卡 VRAM，因此您可能认为您的系统无法使用该 RAM 量。