Re: Missing memory and the mystery of MTRRs
On 2/13/21 11:17 PM, Charlie Gibbs wrote:
> [This would probably be an FAQ if I knew the proper incantation...]
>
> I realized recently that a box I've been running for a while isn't
> seeing all of its installed memory. The BIOS screens indicate that 8GB
> is installed, but Debian (recently upgraded to Buster) only sees a bit
> over 3GB.
>
> cjg@dragon:~$ head -1 /proc/meminfo
> MemTotal: 3331096 kB
>
> During boot I noticed the following message:
>
> [ 0.012080] WARNING: BIOS bug: CPU MTRRs don't cover all of memory,
> losing 4800MB of RAM.
>
> So I guess it's time to start learning about the wonderful world of MTRRs.
>
> cjg@dragon:~$ cat /proc/mtrr
> reg00: base=0x000000000 ( 0MB), size= 2048MB, count=1: write-back
> reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
> reg02: base=0x0c0000000 ( 3072MB), size= 256MB, count=1: write-back
> reg03: base=0x0cff00000 ( 3327MB), size= 1MB, count=1: uncachable
>
> cjg@dragon:~$ head -9 /proc/cpuinfo
> processor : 0
> vendor_id : GenuineIntel
> cpu family : 6
> model : 15
> model name : Intel(R) Core(TM)2 CPU 6300 @ 1.86GHz
> stepping : 2
> microcode : 0x56
> cpu MHz : 1598.388
> cache size : 2048 KB
>
> Here's the first part of /var/log/messages:
>
> [ 0.000000] Linux version 4.19.0-6-amd64
> (debian-kernel@lists.debian.org) (gcc version 8.3.0 (Debian 8.3.0-6)) #1
> SMP Debian 4.19.67-2+deb10u1 (2019-09-20)
> [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.19.0-6-amd64
> root=UUID=4d3143dd-d732-4755-b832-05753ab9c53a ro quiet
> [ 0.000000] x86/fpu: x87 FPU will use FXSAVE
> [ 0.000000] BIOS-provided physical RAM map:
> [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000008efff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x000000000008f000-0x000000000009ffff]
> reserved
> [ 0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff]
> reserved
> [ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000cfd60fff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x00000000cfd61000-0x00000000cfd6dfff]
> reserved
> [ 0.000000] BIOS-e820: [mem 0x00000000cfd6e000-0x00000000cfe1efff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x00000000cfe1f000-0x00000000cfee8fff]
> ACPI NVS
> [ 0.000000] BIOS-e820: [mem 0x00000000cfee9000-0x00000000cfeecfff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x00000000cfeed000-0x00000000cfef1fff]
> ACPI data
> [ 0.000000] BIOS-e820: [mem 0x00000000cfef2000-0x00000000cfef2fff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x00000000cfef3000-0x00000000cfefefff]
> ACPI data
> [ 0.000000] BIOS-e820: [mem 0x00000000cfeff000-0x00000000cfefffff]
> usable
> [ 0.000000] BIOS-e820: [mem 0x00000000cff00000-0x00000000cfffffff]
> reserved
> [ 0.000000] BIOS-e820: [mem 0x00000000fff00000-0x00000000ffffffff]
> reserved
> [ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000022bffffff]
> usable
> [ 0.000000] NX (Execute Disable) protection: active
> [ 0.000000] SMBIOS 2.4 present.
> [ 0.000000] DMI: /DG965WH, BIOS MQ96510J.86A.1687.2007.0510.0258
> 05/10/2007
> [ 0.000000] tsc: Fast TSC calibration using PIT
> [ 0.000000] tsc: Detected 1864.782 MHz processor
> [ 0.011112] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
> [ 0.011115] e820: remove [mem 0x000a0000-0x000fffff] usable
> [ 0.011126] last_pfn = 0x22c000 max_arch_pfn = 0x400000000
> [ 0.011134] MTRR default type: uncachable
> [ 0.011135] MTRR fixed ranges enabled:
> [ 0.011137] 00000-9FFFF write-back
> [ 0.011139] A0000-FFFFF uncachable
> [ 0.011140] MTRR variable ranges enabled:
> [ 0.011142] 0 base 000000000 mask F80000000 write-back
> [ 0.011144] 1 base 080000000 mask FC0000000 write-back
> [ 0.011145] 2 base 0C0000000 mask FF0000000 write-back
> [ 0.011147] 3 base 0CFF00000 mask FFFF00000 uncachable
> [ 0.011148] 4 disabled
> [ 0.011149] 5 disabled
> [ 0.011149] 6 disabled
> [ 0.011150] 7 disabled
> [ 0.011968] x86/PAT: Configuration [0-7]: WB WC UC- UC WB WP UC- WT
> [ 0.012074] e820: update [mem 0xcff00000-0x22bffffff] usable ==>
> reserved
> [ 0.012080] WARNING: BIOS bug: CPU MTRRs don't cover all of memory,
> losing 4800MB of RAM.
>
> Is there some sort of HOWTO that covers this stuff? Where do I go from
> here?
>
Hi Charlie,
try to update your system first.
In your log kernel version is 4.19.67-2+deb10u1 (2019-09-20),
latest in Buster is 4.19.171-2 (2021-01-30).
I am not sure that this update will help you but I guess it won't become
worse.
Kind regards
Georgi
Reply to: