道理我都懂，可是为什么内存 4G 只能识别 3G？？

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This topic created in 3845 days ago, the information mentioned may be changed or developed.

cat /etc/redhat-release
CentOS release 6.6 (Final)Markdown

free -m
total used free shared buffers cached
Mem: 3129

uname -a
Linux gov.jp 2.6.32-504.el6.x86_64 #1 SMP Wed Oct 15 04:27:16 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

图片不会传，看贴吧里的图片吧
http://tieba.baidu.com/p/4107251680

Supplement 1 · Oct 18, 2015

35 层解决了我的问题~
找机房改了 BIOSok 了！！
Mem: 3823

感谢已发送 Reply 35
salmon5 21 分钟前 ♥ 1
http://serverfault.com/questions/81126/linux-x86-64-reports-3-2g-of-memory-instead-of-4g

Go in the BIOS. There should be a Memory Remap Feature option (probably in the Advanced menu) which is disabled by default. Enable it and try again.

37 replies • 2015-10-19 15:47:20 +08:00

GPU

Oct 17, 2015

道理真的懂？
真懂应该不用问这问题把。

aalska

Oct 17, 2015

内核空间？

phoneli

Oct 17, 2015

不正常。

chevalier

Oct 17, 2015

因为要预留出一部分硬件地址空间，给总线上其他设备用

jings

Oct 17, 2015

汪汪姐

tntsec

Oct 17, 2015

@GPU 这要是 256M 占用或者 512 我连问都不问

tntsec

Oct 17, 2015

@aalska 1G 也太大了

tntsec

Oct 17, 2015

@chevalier 1G ？

XiaoxiaoPu

Oct 17, 2015 via Android

64 位系统应该不会是地址空间不够用，难道是被显卡吃掉了？

tntsec

Oct 17, 2015

@XiaoxiaoPu 机房的物理机，这玩意能用命令看吗

XiaoxiaoPu

Oct 17, 2015 via Android

@tntsec 不清楚，我也是猜的。不过你可以把 dmesg 的结果贴出来看看。

flynaj

Oct 17, 2015 via Android

这个主板老了，可能对 4g 内存支持不好

ivenvd

Oct 17, 2015

貌似集成显卡什么的可能会使用共享内存。

nyanpath

Oct 17, 2015

https://www.0.51bbc.workers.dev/t/214082

LGA1150

Oct 17, 2015

32 位系统能使用的最大内存与主板芯片组有关，据我所知， NVIDIA nForce 430 芯片组可以到 3.25G ， AMD A55 芯片组只能到 3.0G ， Intel Z77 可以到 3.5G

eirk2004

Oct 17, 2015

@LGA1150 戏服合格。与 BIOS 和系统都有关系。当时有块华硕 P55 主板，可以利用到 3.5G ，同类主板一般是 3.25G 。内存超过 3G 以后，操作系统划走一部分资源给外围设备。最新的 CPU 集成了显卡，再占用 256MB 左右，实际可用不足 3G 。
参考： https://en.wikipedia.org/wiki/3_GB_barrier

SonicY

Oct 17, 2015

可能用的 g31 的集显？都有啥 pci 设备？

Starduster

Oct 18, 2015

什么芯片组。。。。我 IBM T60 因为主板（ 945M ）不支持所以只读的出 3G 内存

xierch

Oct 18, 2015

可是鸽子为什么这么大？

vibbow

Oct 18, 2015

才 1G ，我有台笔记本要占 1.25G 我会乱说？

yxaaa123

Oct 18, 2015

1g 给显卡了

wuxqing

Oct 18, 2015

用 dmesg | grep reserved
看看是不是被系统预留了

VYSE

Oct 18, 2015 via Android

咋还有说 32 位的，人家就是 x86_64 ，楼主去 bios 里看看可用内存就知道。例如 INTEL 945 之前的 memory-mapped I/O 与物理内存冲突干脆直接 bios 强行封印物理内存，有的封印多有的封印少。

gamexg

Oct 18, 2015

楼主的是 64 位系统...

Ouyangan

Oct 18, 2015

核显占用了吧

realpg

PRO

Oct 18, 2015

换主板。
你这主板就这样了，主板自身最高支持内存 4G ，且映射进系统时候会屏蔽不少内存。
G31 这玩意还用着呢……

chevalier

Oct 18, 2015

@tntsec 不到 1G ， Windows 下面我看大概是 700M 左右

clink8001

Oct 18, 2015

操作系统也是软件，他的存在本身是要占用一部分内存的，剩下的才是可用的内存。

yksoft1

Oct 18, 2015

其实在某些笔记本上还可能小于 3GB

chenai00

Oct 18, 2015

真的是汪汪姐？😀😀😀

tntsec

Oct 18, 2015

@wuxqing dmesg | grep reserved
BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000e6000 - 0000000000100000 (reserved)
BIOS-e820: 00000000cf6f0000 - 00000000cf700000 (reserved)
BIOS-e820: 00000000fed00000 - 00000000fed00400 (reserved)
BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
BIOS-e820: 00000000ff380000 - 0000000100000000 (reserved)
e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
e820 update range: 0000000000000000 - 0000000000001000 (usable) ==> (reserved)
#4 [000009f800 - 0000100000] BIOS reserved ==> [000009f800 - 0000100000]
DMA zone: 103 pages reserved
Memory: 3182444k/3398336k available (5336k kernel code, 452k absent, 215440k reserved, 7016k data, 1292k init)
PCI: MCFG area at e0000000 reserved in ACPI motherboard resources
system 00:01: [mem 0xfed14000-0xfed19fff] has been reserved
system 00:07: [io 0x04d0-0x04d1] has been reserved
system 00:07: [io 0x0800-0x087f] has been reserved
system 00:07: [io 0x0480-0x04bf] has been reserved
system 00:07: [io 0x0900-0x090f] has been reserved
system 00:07: [mem 0xfed1c000-0xfed1ffff] has been reserved
system 00:07: [mem 0xfed20000-0xfed8ffff] has been reserved
system 00:09: [mem 0xffc00000-0xfff7ffff] has been reserved
system 00:0a: [mem 0xfec00000-0xfec00fff] could not be reserved
system 00:0a: [mem 0xfee00000-0xfee00fff] has been reserved
system 00:0c: [io 0x0280-0x028f] has been reserved
system 00:0c: [io 0x0290-0x029f] has been reserved
system 00:0d: [mem 0xe0000000-0xefffffff] has been reserved
system 00:0e: [mem 0x00000000-0x0009ffff] could not be reserved
system 00:0e: [mem 0x000e0000-0x000fffff] could not be reserved
system 00:0e: [mem 0x00100000-0xcf6fffff] could not be reserved

tntsec

Oct 18, 2015

@xierch 哈哈哈，看来你懂这个梗~

javaluo

Oct 18, 2015 via Android

@tntsec however 节点？

tntsec

Oct 18, 2015

@javaluo 啥？不懂

salmon5

Oct 18, 2015

http://serverfault.com/questions/81126/linux-x86-64-reports-3-2g-of-memory-instead-of-4g

Go in the BIOS. There should be a Memory Remap Feature option (probably in the Advanced menu) which is disabled by default. Enable it and try again.

tntsec

Oct 18, 2015

@salmon5
Mem: 3823

OK ！！

他还感谢我，啊哈哈

You are welcome :) Thank you for showing us how to resolve that issue.

lyz1990

Oct 19, 2015

道理我都懂啊，可是我 16G 的内存在 64 位 Ubuntu 上也是显示的 15.4G 　啊