我有一台 ThinkPad P14s Gen 2 AMD，配备 AMD Ryzen 7 PRO 5850U，配备 Vega 8 显卡，运行 Fedora 34。它安装了一个 16GB DIMM，BIOS 和 dmideocde 均正确报告
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: 16 GB
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
然而，free、htop 等仅报告 12GB 可用
total used free shared buff/cache available
Mem: 12063100 4728904 1619056 172620 5715140 6852240
Swap: 8388604 0 8388604
所以我看了一下其他 4GB 丢失的地方，并memory在 dmesg 中查找并得到了
[ 0.004454] ACPI: Reserving FACP table memory at [mem 0xc5993000-0xc5993113]
[ 0.004455] ACPI: Reserving DSDT table memory at [mem 0xc597c000-0xc598d8ca]
[ 0.004456] ACPI: Reserving FACS table memory at [mem 0xcbc19000-0xcbc1903f]
[ 0.004456] ACPI: Reserving SSDT table memory at [mem 0xc7c9c000-0xc7c9c0a1]
[ 0.004457] ACPI: Reserving SSDT table memory at [mem 0xc7c9a000-0xc7c9b18e]
[ 0.004457] ACPI: Reserving SSDT table memory at [mem 0xc7c8c000-0xc7c93228]
[ 0.004458] ACPI: Reserving IVRS table memory at [mem 0xc7c6a000-0xc7c6a1a3]
[ 0.004458] ACPI: Reserving SSDT table memory at [mem 0xc7c38000-0xc7c38a41]
[ 0.004459] ACPI: Reserving SSDT table memory at [mem 0xc7bb3000-0xc7bb3631]
[ 0.004459] ACPI: Reserving TPM2 table memory at [mem 0xc7bb2000-0xc7bb2033]
[ 0.004460] ACPI: Reserving POAT table memory at [mem 0xc7baf000-0xc7baf054]
[ 0.004460] ACPI: Reserving BATB table memory at [mem 0xc7b9a000-0xc7b9a049]
[ 0.004460] ACPI: Reserving HPET table memory at [mem 0xc5992000-0xc5992037]
[ 0.004461] ACPI: Reserving APIC table memory at [mem 0xc5991000-0xc5991137]
[ 0.004461] ACPI: Reserving MCFG table memory at [mem 0xc5990000-0xc599003b]
[ 0.004462] ACPI: Reserving SBST table memory at [mem 0xc598f000-0xc598f02f]
[ 0.004462] ACPI: Reserving WSMT table memory at [mem 0xc598e000-0xc598e027]
[ 0.004463] ACPI: Reserving VFCT table memory at [mem 0xc596e000-0xc597b883]
[ 0.004463] ACPI: Reserving SSDT table memory at [mem 0xc5968000-0xc596d353]
[ 0.004464] ACPI: Reserving CRAT table memory at [mem 0xc5967000-0xc5967ebf]
[ 0.004464] ACPI: Reserving CDIT table memory at [mem 0xc5966000-0xc5966028]
[ 0.004465] ACPI: Reserving FPDT table memory at [mem 0xc7b9b000-0xc7b9b033]
[ 0.004465] ACPI: Reserving SSDT table memory at [mem 0xc5965000-0xc5965148]
[ 0.004466] ACPI: Reserving SSDT table memory at [mem 0xc5963000-0xc59644ba]
[ 0.004466] ACPI: Reserving SSDT table memory at [mem 0xc5961000-0xc596257f]
[ 0.004467] ACPI: Reserving SSDT table memory at [mem 0xc595d000-0xc5960972]
[ 0.004467] ACPI: Reserving BGRT table memory at [mem 0xc595c000-0xc595c037]
[ 0.004468] ACPI: Reserving UEFI table memory at [mem 0xcbc18000-0xcbc180d9]
[ 0.004468] ACPI: Reserving SSDT table memory at [mem 0xc595b000-0xc595b051]
[ 0.004469] ACPI: Reserving SSDT table memory at [mem 0xc7c98000-0xc7c9808f]
[ 0.004469] ACPI: Reserving SSDT table memory at [mem 0xc7c97000-0xc7c979b4]
[ 0.028600] Early memory node ranges
[ 0.057390] PM: hibernation: Registered nosave memory: [mem 0x00000000-0x00000fff]
[ 0.057392] PM: hibernation: Registered nosave memory: [mem 0x0009f000-0x0009ffff]
[ 0.057392] PM: hibernation: Registered nosave memory: [mem 0x000a0000-0x000dffff]
[ 0.057392] PM: hibernation: Registered nosave memory: [mem 0x000e0000-0x000fffff]
[ 0.057393] PM: hibernation: Registered nosave memory: [mem 0x09c00000-0x09da0fff]
[ 0.057394] PM: hibernation: Registered nosave memory: [mem 0x09f00000-0x09f0cfff]
[ 0.057395] PM: hibernation: Registered nosave memory: [mem 0x995b4000-0x995b4fff]
[ 0.057396] PM: hibernation: Registered nosave memory: [mem 0x995c1000-0x995c1fff]
[ 0.057397] PM: hibernation: Registered nosave memory: [mem 0xc0587000-0xc0617fff]
[ 0.057397] PM: hibernation: Registered nosave memory: [mem 0xc09bd000-0xc09bdfff]
[ 0.057398] PM: hibernation: Registered nosave memory: [mem 0xc1bee000-0xc1beefff]
[ 0.057399] PM: hibernation: Registered nosave memory: [mem 0xc4b7e000-0xcad7dfff]
[ 0.057399] PM: hibernation: Registered nosave memory: [mem 0xcad7e000-0xcbd7dfff]
[ 0.057400] PM: hibernation: Registered nosave memory: [mem 0xcbd7e000-0xcbdfdfff]
[ 0.057401] PM: hibernation: Registered nosave memory: [mem 0xce000000-0xcfffffff]
[ 0.057401] PM: hibernation: Registered nosave memory: [mem 0xd0000000-0xf7ffffff]
[ 0.057401] PM: hibernation: Registered nosave memory: [mem 0xf8000000-0xfbffffff]
[ 0.057402] PM: hibernation: Registered nosave memory: [mem 0xfc000000-0xfdbfffff]
[ 0.057402] PM: hibernation: Registered nosave memory: [mem 0xfdc00000-0xfdcfffff]
[ 0.057402] PM: hibernation: Registered nosave memory: [mem 0xfdd00000-0xfed7ffff]
[ 0.057403] PM: hibernation: Registered nosave memory: [mem 0xfed80000-0xfed80fff]
[ 0.057403] PM: hibernation: Registered nosave memory: [mem 0xfed81000-0xffffffff]
[ 0.100832] Memory: 11910836K/12401088K available (16393K kernel code, 3512K rwdata, 9992K rodata, 2792K init, 5048K bss, 489992K reserved, 0K cma-reserved)
[ 0.127550] Freeing SMP alternatives memory: 44K
[ 0.250903] x86/mm: Memory block size: 128MB
[ 0.453344] Non-volatile memory driver v1.3
[ 0.636368] Freeing initrd memory: 41780K
[ 0.705257] Freeing unused decrypted memory: 2036K
[ 0.705739] Freeing unused kernel image (initmem) memory: 2792K
[ 0.710554] Freeing unused kernel image (text/rodata gap) memory: 2036K
[ 0.710723] Freeing unused kernel image (rodata/data gap) memory: 248K
[ 1.449478] amdgpu 0000:07:00.0: amdgpu: Trusted Memory Zone (TMZ) feature enabled
[ 1.545656] [drm] amdgpu: 4096M of VRAM memory ready
[ 1.545659] [drm] amdgpu: 4096M of GTT memory ready.
我发现其中有趣的是，似乎 4GB 完全保留给 GPU（由于 TMZ？）。那是我另外 4GB 的地方吗丢失的？如果是的话，有什么办法可以解决这个问题（这是一个聪明的想法吗）？如果不是，我的其他 4GB 去哪儿了？
提前致谢 ：）
答案1
这可以在 BIOS 中的 UMA 帧缓冲区大小下更改。现在可能是自动，您可以将其更改为512M、1G、2G和4G