Arch Linux

skiesbleed

Member

Registered: 2015-08-11

Posts: 2

Only 3.3GB of RAM Showing Up on Arch x86_64

I'm having an issue where only 3.3GB of my 4GiB of installed RAM is showing up. This was installed fresh as an x86_64 build, so there wasn't any cross-over that happened at any point. Here are the relevant outputs from my system:

skiesbleed@hivemind:~$ sudo lshw -class memory | grep GiB
       size: 4GiB
          size: 4GiB
skiesbleed@hivemind:~$ uname -a
Linux hivemind 4.1.3-1-ARCH #1 SMP PREEMPT Wed Jul 22 20:37:12 CEST 2015 x86_64 GNU/Linux
skiesbleed@hivemind:~$ free -m
              total        used        free      shared  buff/cache   available
Mem:           3347        1147         624           0        1575        2151
Swap:          8386          33        8353
skiesbleed@hivemind:~$ grep "^flags.*\blm\b" /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc extd_apicid aperfmperf eagerfpu pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 popcnt aes xsave avx f16c lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce nodeid_msr tbm topoext perfctr_core perfctr_nb bpext arat cpb hw_pstate npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold vmmcall fsgsbase bmi1 xsaveopt

Does anyone have any ideas what's going on here or how I can fix it? Any and all help would be appreciated.

djgera

Developer

From: Buenos Aires - Argentina

Registered: 2008-12-24

Posts: 723

Website

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

Remap "pci" memory in bios or something like that. In this case The "olverlapped" PCI physical address space, is remaped beyond 4G physical address space. Look at e820 calls (first lines at dmesg) to see how physical memory is organized.

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,659

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

Also, what kind of video card to you have?  Some of that memory may have been stolen as a frame buffer.  Check your journal.  Search for memory or stolen.

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DarkCerberus

Banned

From: Holsworthy, Devon

Registered: 2011-12-31

Posts: 252

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

What's your system specs? Was it pre-2007 or after-2007 it could be the computer hasn't got a 64-bit processor though it should detect it since yours was able to run the 64-bit archlinux also what about trying the pae linux kernel this is known if I'm correct to increase the RAM to full....

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nomorewindows

Member

Registered: 2010-04-03

Posts: 3,541

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

Could be address lines, not all 64-bit processors will do much with 4G.

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Slithery

Administrator

From: Norfolk, UK

Registered: 2013-12-01

Posts: 5,776

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

...it could be the computer hasn't got a 64-bit processor though it should detect it since yours was able to run the 64-bit archlinux....

If it's running 64-bit arch it must have a 64-bit processor.

...also what about trying the pae linux kernel this is known if I'm correct to increase the RAM to full....

The PAE kernel is 32-bit only, it doesn't make sense on a 64-bit machine as its only purpose is to allow 32-bit machines to address more than 4GB of RAM.

You should also read what Linus has to say about PAE before deciding whether or not to use it...
https://cl4ssic4l.wordpress.com/2011/05 … about-pae/

Last edited by Slithery (2015-08-11 17:21:13)

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skiesbleed

Member

Registered: 2015-08-11

Posts: 2

Re: Only 3.3GB of RAM Showing Up on Arch x86_64

Remap "pci" memory in bios or something like that. In this case The "olverlapped" PCI physical address space, is remaped beyond 4G physical address space. Look at e820 calls (first lines at dmesg) to see how physical memory is organized.

It doesn't seem like this is what's happening, if I'm reading the e820 output correctly. I do see reserved spots higher up in the memory, but I did some searching online and it sounds like this kind of PCI memory usage is typically in the first part of the address space. The only reservation I see here is for 0x0000 to 0x0fff, which is negligible and seems to be done by the kernel itself since it's applied as an update. I don't have an option in my BIOS for PCI Memory Remapping, so if it is the problem, then I guess I'm out of luck.  For posterity, here is the e820 debug:

skiesbleed@hivemind:~$ dmesg | grep e820
[    0.000000] e820: BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000009e283fff] usable
[    0.000000] BIOS-e820: [mem 0x000000009e284000-0x000000009e2b3fff] reserved
[    0.000000] BIOS-e820: [mem 0x000000009e2b4000-0x000000009e2e8fff] usable
[    0.000000] BIOS-e820: [mem 0x000000009e2e9000-0x000000009e3a4fff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x000000009e3a5000-0x000000009ea36fff] reserved
[    0.000000] BIOS-e820: [mem 0x000000009ea37000-0x000000009ea37fff] usable
[    0.000000] BIOS-e820: [mem 0x000000009ea38000-0x000000009ec3dfff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x000000009ec3e000-0x000000009f081fff] usable
[    0.000000] BIOS-e820: [mem 0x000000009f082000-0x000000009f7f2fff] reserved
[    0.000000] BIOS-e820: [mem 0x000000009f7f3000-0x000000009f7fffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000e0000000-0x00000000efffffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000feb80000-0x00000000fec01fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed00000-0x00000000fed00fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed40000-0x00000000fed44fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed80000-0x00000000fed8ffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000013effffff] usable
[    0.000000] e820: update [mem 0x8bb78018-0x8bb87657] usable ==> usable
[    0.000000] e820: update [mem 0x8bb6a018-0x8bb77057] usable ==> usable
[    0.000000] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.000000] e820: last_pfn = 0x13f000 max_arch_pfn = 0x400000000
[    0.000000] e820: update [mem 0x9f800000-0xffffffff] usable ==> reserved
[    0.000000] e820: last_pfn = 0x9f800 max_arch_pfn = 0x400000000
[    0.000000] e820: [mem 0x9f800000-0xdfffffff] available for PCI devices
[    0.352243] e820: reserve RAM buffer [mem 0x8bb6a018-0x8bffffff]
[    0.352244] e820: reserve RAM buffer [mem 0x8bb78018-0x8bffffff]
[    0.352246] e820: reserve RAM buffer [mem 0x9e284000-0x9fffffff]
[    0.352247] e820: reserve RAM buffer [mem 0x9e2e9000-0x9fffffff]
[    0.352248] e820: reserve RAM buffer [mem 0x9ea38000-0x9fffffff]
[    0.352249] e820: reserve RAM buffer [mem 0x9f082000-0x9fffffff]
[    0.352250] e820: reserve RAM buffer [mem 0x9f800000-0x9fffffff]
[    0.352252] e820: reserve RAM buffer [mem 0x13f000000-0x13fffffff]

Also, what kind of video card to you have?  Some of that memory may have been stolen as a frame buffer.  Check your journal.  Search for memory or stolen.

This is a headless unit, so I didn't think of this. This is an AMD APU, and it does indeed look like the integrated graphics card is reserving 512MB of RAM:

skiesbleed@hivemind:~$ dmesg | grep drm
...
[    6.013840] [drm] Detected VRAM RAM=512M, BAR=256M
[    6.013842] [drm] RAM width 128bits DDR
[    6.016026] [drm] radeon: 512M of VRAM memory ready
[    6.016028] [drm] radeon: 1024M of GTT memory ready.
...

From what I've read online, there's not really anything I can do about this. I double-checked my BIOS just in case, but I don't have any options to disable this or change the size.

There does still seem to be some memory unaccounted for, though. After the 512M for the integrated graphics card has been taken from the memory pool, there is still another 424376K that is reserved, but I don't know what for:

skiesbleed@hivemind:~$ dmesg | grep Memory
[    0.000000] Memory: 3203312K/3627688K available (5699K kernel code, 893K rwdata, 1732K rodata, 1180K init, 1152K bss, 424376K reserved, 0K cma-reserved)

Now, neither of the values shown here line up with the total presented in free -mk (3428196), so perhaps I'm just misunderstanding something here?