linux-kernel - Re: memory beyond4GB invisible to the system even though CONFIG

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Date:	Tue, 13 Jan 2009 18:22:19 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	"James Kirin" <james.kirin40@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: memory beyond4GB invisible to the system even though CONFIG_HIGHMEM64G=y

 > I am running kernel 2.6.28 on a computer with 8GB RAM. The BIOS
 > detects all 8GB, yet
 > 
 > jk@...2:~$ free
 >              total       used       free     shared    buffers     cached
 > Mem:       3622504     799696    2822808          0      90936     369604
 > -/+ buffers/cache:     339156    3283348
 > Swap:      6867776          0    6867776

The message in your kernel log:

[    0.000000] WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing 4096MB of RAM.
[    0.000000] ------------[ cut here ]------------
[    0.000000] WARNING: at arch/x86/kernel/cpu/mtrr/main.c:1662 mtrr_trim_uncached_memory+0x283/0x2a4()

is a clue.  You might want to look for a BIOS update for your
motherboard.

 - R.
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