'free' 和 '/proc/meminfo/ 报告的总内存比 'dmidecode' 少

Question

我们在主机托管的服务器（一个真正的物理服务器，而不是一个VM），运行64位的Debian（ ：）。uname -r3.16.0-4-amd64

/proc/meminfo报告大约 4 GiB 总内存：

$ head -n 1 /proc/meminfo
MemTotal:        4051692 kB

free报告相同（我只看了total专栏；我不是在谈论已用、免费、共享、缓冲区、缓存）：

$ free -k
             total       used       free     shared    buffers     cached
Mem:       4051692    3867356     184336     220908      63948    1203596
-/+ buffers/cache:    2599812    1451880
Swap:     15728208     652540   15075668

也是如此dmesg | grep Memory：

$ dmesg | grep Memory
[    0.000000] Memory: 4034240K/4185236K available (5287K kernel code, 949K rwdata, 1836K rodata, 1208K init, 840K bss, 150996K reserved)

但是 dmidecode 报告 4 * 2 GiB = 8 GiB 的 RAM，如果我理解正确的话：

$ sudo dmidecode --type memory

# dmidecode 2.12
SMBIOS 2.6 present.

Handle 0x0008, DMI type 5, 24 bytes
Memory Controller Information
    Error Detecting Method: 64-bit ECC
    Error Correcting Capabilities:
        Single-bit Error Correcting
    Supported Interleave: One-way Interleave
    Current Interleave: One-way Interleave
    Maximum Memory Module Size: 4096 MB
    Maximum Total Memory Size: 16384 MB
    Supported Speeds:
        Other
    Supported Memory Types:
        DIMM
        SDRAM
    Memory Module Voltage: 3.3 V
    Associated Memory Slots: 4
        0x0009
        0x000A
        0x000B
        0x000C
    Enabled Error Correcting Capabilities:
        Single-bit Error Correcting

Handle 0x0009, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM1A
    Bank Connections: 0 1
    Current Speed: Unknown
    Type: DIMM SDRAM
    Installed Size: 2048 MB (Single-bank Connection)
    Enabled Size: 2048 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000A, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM1B
    Bank Connections: 2 3
    Current Speed: Unknown
    Type: DIMM SDRAM
    Installed Size: 2048 MB (Single-bank Connection)
    Enabled Size: 2048 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000B, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM2A
    Bank Connections: 4 5
    Current Speed: Unknown
    Type: DIMM SDRAM
    Installed Size: 2048 MB (Single-bank Connection)
    Enabled Size: 2048 MB (Single-bank Connection)
    Error Status: OK

Handle 0x000C, DMI type 6, 12 bytes
Memory Module Information
    Socket Designation: DIMM2B
    Bank Connections: 6 7
    Current Speed: Unknown
    Type: DIMM SDRAM
    Installed Size: 2048 MB (Single-bank Connection)
    Enabled Size: 2048 MB (Single-bank Connection)
    Error Status: OK

Handle 0x002A, DMI type 16, 15 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: Single-bit ECC
    Maximum Capacity: 16 GB
    Error Information Handle: Not Provided
    Number Of Devices: 4

Handle 0x002C, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x002A
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM1A
    Bank Locator: BANK0
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Micron        
    Serial Number: 501C6FDC
    Asset Tag: AssetTagNum0
    Part Number: 9JSF25672AZ-1G4D1 
    Rank: Unknown

Handle 0x002E, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x002A
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM1B
    Bank Locator: BANK1
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Micron        
    Serial Number: 2A1C6FDC
    Asset Tag: AssetTagNum1
    Part Number: 9JSF25672AZ-1G4D1 
    Rank: Unknown

Handle 0x0030, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x002A
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM2A
    Bank Locator: BANK2
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Micron        
    Serial Number: 511C6FDC
    Asset Tag: AssetTagNum2
    Part Number: 9JSF25672AZ-1G4D1 
    Rank: Unknown

Handle 0x0032, DMI type 17, 28 bytes
Memory Device
    Array Handle: 0x002A
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 2048 MB
    Form Factor: DIMM
    Set: None
    Locator: DIMM2B
    Bank Locator: BANK3
    Type: DDR3
    Type Detail: Synchronous
    Speed: 1333 MHz
    Manufacturer: Micron        
    Serial Number: 4B1C6FDC
    Asset Tag: AssetTagNum3
    Part Number: 9JSF25672AZ-1G4D1 
    Rank: Unknown

我错过了什么？它是托管中心的服务器，所以不幸的是，我无法轻松查看实际安装的内容。

编辑： man dmidecode说“通常情况下，DMI 表中包含的信息不准确、不完整或完全错误。”。也许 dmidecode 只是报告错误的数据？

编辑：这不是为什么 Linux 奇怪地报告“空闲”内存？. 这个问题是关于空闲内存，以及缓冲区和缓存从中带走的混乱。我不关心空闲内存，只关心总内存。不要让我对free命令的使用愚弄你：我没有用它来查看可用内存量，只查看总内存量。如果有人仍然认为这个问题是重复的，请解释原因，因为我不明白。

编辑：dmidecode -t1根据Lenniey的要求

$ sudo dmidecode -t1
# dmidecode 2.12
SMBIOS 2.6 present.

Handle 0x0001, DMI type 1, 27 bytes
System Information
        Manufacturer: Supermicro
        Product Name: X8SIL
        Version: 0123456789
        Serial Number: 0123456789
        UUID: 49434D53-0200-9037-2500-379025009946
        Wake-up Type: Power Switch
        SKU Number: To Be Filled By O.E.M.
        Family: To Be Filled By O.E.M.

Answer 1

事实证明，其中一个内存模块出现故障，导致系统忽略同一通道中的该内存模块和另一个内存模块。

现在我们的办公室里有服务器，我们看到确实有 4 个 DIMM 模块，每个 2 GB。我把模块一一测试了一下，发现有一个有问题。

（这并不能解释为什么 dmidecode 对所有四个模块都显示“错误状态：正常”。我想这可以通过引用“DMI 表中包含的信息通常不准确、不完整或根本错误”来解释。在手册页中）