我目前在笔记本电脑上运行 Ubuntu。根据我的规格并查看我的 BIOS，应该有 16GiB 的 RAM。我第一次拿到它时有 16GiB 的 RAM，但无论我何时打电话free或htop现在，它都只显示 12GiB。输出为free：
total used free shared buff/cache available
Mem: 12077124 1817484 8333912 18500 1925728 9965952
Swap: 33554428 0 33554428
输出为dmesg | grep -i memory：
[ 0.004350] check: Scanning 1 areas for low memory corruption
[ 0.004667] ACPI: Reserving FACP table memory at [mem 0xc5993000-0xc5993113]
[ 0.004668] ACPI: Reserving DSDT table memory at [mem 0xc597c000-0xc598d8ca]
[ 0.004669] ACPI: Reserving FACS table memory at [mem 0xcbc19000-0xcbc1903f]
[ 0.004669] ACPI: Reserving SSDT table memory at [mem 0xc7c9c000-0xc7c9c0a1]
[ 0.004670] ACPI: Reserving SSDT table memory at [mem 0xc7c9a000-0xc7c9b18e]
[ 0.004670] ACPI: Reserving SSDT table memory at [mem 0xc7c8c000-0xc7c93228]
[ 0.004671] ACPI: Reserving IVRS table memory at [mem 0xc7c6a000-0xc7c6a1a3]
[ 0.004671] ACPI: Reserving SSDT table memory at [mem 0xc7c38000-0xc7c38a41]
[ 0.004672] ACPI: Reserving SSDT table memory at [mem 0xc7bb3000-0xc7bb3631]
[ 0.004672] ACPI: Reserving TPM2 table memory at [mem 0xc7bb2000-0xc7bb2033]
[ 0.004673] ACPI: Reserving POAT table memory at [mem 0xc7baf000-0xc7baf054]
[ 0.004673] ACPI: Reserving BATB table memory at [mem 0xc7b9a000-0xc7b9a049]
[ 0.004674] ACPI: Reserving HPET table memory at [mem 0xc5992000-0xc5992037]
[ 0.004675] ACPI: Reserving APIC table memory at [mem 0xc5991000-0xc5991137]
[ 0.004675] ACPI: Reserving MCFG table memory at [mem 0xc5990000-0xc599003b]
[ 0.004676] ACPI: Reserving SBST table memory at [mem 0xc598f000-0xc598f02f]
[ 0.004676] ACPI: Reserving WSMT table memory at [mem 0xc598e000-0xc598e027]
[ 0.004677] ACPI: Reserving VFCT table memory at [mem 0xc596e000-0xc597b883]
[ 0.004677] ACPI: Reserving SSDT table memory at [mem 0xc5968000-0xc596d353]
[ 0.004678] ACPI: Reserving CRAT table memory at [mem 0xc5967000-0xc5967ebf]
[ 0.004679] ACPI: Reserving CDIT table memory at [mem 0xc5966000-0xc5966028]
[ 0.004679] ACPI: Reserving FPDT table memory at [mem 0xc7b9b000-0xc7b9b033]
[ 0.004680] ACPI: Reserving SSDT table memory at [mem 0xc5965000-0xc5965148]
[ 0.004680] ACPI: Reserving SSDT table memory at [mem 0xc5963000-0xc59644ba]
[ 0.004681] ACPI: Reserving SSDT table memory at [mem 0xc5961000-0xc596257f]
[ 0.004681] ACPI: Reserving SSDT table memory at [mem 0xc595d000-0xc5960972]
[ 0.004682] ACPI: Reserving BGRT table memory at [mem 0xc595c000-0xc595c037]
[ 0.004683] ACPI: Reserving SSDT table memory at [mem 0xc595b000-0xc595b057]
[ 0.004683] ACPI: Reserving SSDT table memory at [mem 0xc595a000-0xc595a24c]
[ 0.004684] ACPI: Reserving SSDT table memory at [mem 0xc5958000-0xc59592bb]
[ 0.004684] ACPI: Reserving SSDT table memory at [mem 0xc5957000-0xc5957ad4]
[ 0.004685] ACPI: Reserving UEFI table memory at [mem 0xcbc18000-0xcbc180d9]
[ 0.004685] ACPI: Reserving SSDT table memory at [mem 0xc5956000-0xc5956051]
[ 0.004686] ACPI: Reserving SSDT table memory at [mem 0xc7c98000-0xc7c9808f]
[ 0.004687] ACPI: Reserving SSDT table memory at [mem 0xc7c97000-0xc7c979b4]
[ 0.004947] Early memory node ranges
[ 0.032537] PM: hibernation: Registered nosave memory: [mem 0x00000000-0x00000fff]
[ 0.032539] PM: hibernation: Registered nosave memory: [mem 0x0009f000-0x0009ffff]
[ 0.032539] PM: hibernation: Registered nosave memory: [mem 0x000a0000-0x000dffff]
[ 0.032540] PM: hibernation: Registered nosave memory: [mem 0x000e0000-0x000fffff]
[ 0.032541] PM: hibernation: Registered nosave memory: [mem 0x09c00000-0x09da0fff]
[ 0.032542] PM: hibernation: Registered nosave memory: [mem 0x09f00000-0x09f0cfff]
[ 0.032542] PM: hibernation: Registered nosave memory: [mem 0x9973c000-0x9973cfff]
[ 0.032543] PM: hibernation: Registered nosave memory: [mem 0x99749000-0x99749fff]
[ 0.032544] PM: hibernation: Registered nosave memory: [mem 0xc0a5b000-0xc0aebfff]
[ 0.032545] PM: hibernation: Registered nosave memory: [mem 0xc1214000-0xc1214fff]
[ 0.032546] PM: hibernation: Registered nosave memory: [mem 0xc1bee000-0xc1beefff]
[ 0.032547] PM: hibernation: Registered nosave memory: [mem 0xc4b7e000-0xcad7dfff]
[ 0.032548] PM: hibernation: Registered nosave memory: [mem 0xcad7e000-0xcbd7dfff]
[ 0.032548] PM: hibernation: Registered nosave memory: [mem 0xcbd7e000-0xcbdfdfff]
[ 0.032549] PM: hibernation: Registered nosave memory: [mem 0xce000000-0xcfffffff]
[ 0.032549] PM: hibernation: Registered nosave memory: [mem 0xd0000000-0xf7ffffff]
[ 0.032550] PM: hibernation: Registered nosave memory: [mem 0xf8000000-0xfbffffff]
[ 0.032550] PM: hibernation: Registered nosave memory: [mem 0xfc000000-0xfdbfffff]
[ 0.032551] PM: hibernation: Registered nosave memory: [mem 0xfdc00000-0xfdcfffff]
[ 0.032551] PM: hibernation: Registered nosave memory: [mem 0xfdd00000-0xfed7ffff]
[ 0.032551] PM: hibernation: Registered nosave memory: [mem 0xfed80000-0xfed80fff]
[ 0.032552] PM: hibernation: Registered nosave memory: [mem 0xfed81000-0xffffffff]
[ 0.071132] Memory: 11923324K/12401088K available (14345K kernel code, 3478K rwdata, 10340K rodata, 2688K init, 5976K bss, 477504K reserved, 0K cma-reserved)
[ 0.109279] Freeing SMP alternatives memory: 40K
[ 0.255382] x86/mm: Memory block size: 128MB
[ 0.633239] Freeing initrd memory: 56768K
[ 0.636859] check: Scanning for low memory corruption every 60 seconds
[ 0.922923] Freeing unused decrypted memory: 2036K
[ 0.923550] Freeing unused kernel image (initmem) memory: 2688K
[ 0.936446] Freeing unused kernel image (text/rodata gap) memory: 2036K
[ 0.937019] Freeing unused kernel image (rodata/data gap) memory: 1948K
[ 2.777602] Non-volatile memory driver v1.3
[ 3.074212] amdgpu 0000:07:00.0: amdgpu: Trusted Memory Zone (TMZ) feature disabled as experimental (default)
[ 3.314687] [TTM] Zone kernel: Available graphics memory: 6038562 KiB
[ 3.314688] [TTM] Zone dma32: Available graphics memory: 2097152 KiB
[ 3.314780] [drm] amdgpu: 4096M of VRAM memory ready
[ 3.314782] [drm] amdgpu: 4096M of GTT memory ready.
我真的不知道我在寻找什么，希望得到任何建议。尤其是它显示了它并且我能够使用它，这让我很困惑。我可能做错了什么？
更新 1：我运行了sudo dmidecode -t memory，结果显示：
# dmidecode 3.2
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 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, 92 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: 3200 MT/s
Manufacturer: Hynix
Serial Number: 00000000
Asset Tag: Not Specified
Part Number: HMAB2GS6AMR6N-XN
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 0xAD
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 0x000B, DMI type 17, 92 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: Null
Serial Number: Null
Asset Tag: Not Specified
Part Number: Null
Rank: Unknown
Configured Memory Speed: Unknown
Minimum Voltage: Unknown
Maximum Voltage: Unknown
Configured Voltage: Unknown
Memory Technology: Unknown
Memory Operating Mode Capability: Unknown
Firmware Version: Unknown
Module Manufacturer ID: Unknown
Module Product ID: Unknown
Memory Subsystem Controller Manufacturer ID: Unknown
Memory Subsystem Controller Product ID: Unknown
Non-Volatile Size: None
Volatile Size: None
Cache Size: None
Logical Size: None
更新 2：我的规格是：
CPU: AMD Ryzen™ 7 PRO (5850U)
GPU: Radeon RX Vega 8
RAM: 16 GB DDR4 3200 MHz (I don't know the company)
答案1
Ubuntu 无法检测到所有已安装的 RAM 容量，可能是因为其中一个 RAM 条出现硬件故障，可以选择用具有相同类型、容量和时钟速度的新 RAM 条替换该 RAM 条，以将 RAM 容量恢复到其原始的 16GB。运行以下命令显示所有 RAM 插槽以及每个插槽中是否安装了 RAM 条。
sudo dmidecode -t memory
部分结果示例sudo dmidecode -t memory：
设备数量：4
句柄 0x0011，DMI 类型 17，84 字节
记忆装置
数组句柄：0x0009
错误信息句柄：0x0010
总宽度：未知
数据宽度：未知
尺寸：未安装模块
上述示例的完整结果将显示主机有 4 个 RAM 插槽，其中两个插槽目前已安装 RAM 模块。它还将显示每个已安装 RAM 模块的容量以及主机的最大 RAM 容量。
答案2
这个答案主要由 jawtheshark 在评论中提供。我将在这里总结一下以解决问题。问题是 Linux 占用了集成 GPU 的一部分 RAM 并将其用作 VRAM。APU 的图形部分保留了 4GB 的系统 RAM 供其使用。查看此内核文档：kernel.org/doc/html/latest/gpu/amdgpu.html 参数：vramlimit (int) --> 限制用于测试的 MiB 中的 VRAM 总量。默认值为 0（使用完整 VRAM）。这意味着将 RAM 委托给集成 GPU 的“自动”选项会将大量 RAM 委托给 GPU。由于我只将机器用作工作站，因此我将在 bios 中将“自动”选项设置为“1 GB”（最小值）。