lkml.org 
[lkml]   [2008]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Does Linux have plan to support memory hole remapping?
On Wed, Apr 09, 2008 at 05:04:24PM +0800, Zhao Forrest wrote:
> On 4/9/08, Andi Kleen <andi@firstfloor.org> wrote:
> > "Zhao Forrest" <forrest.zhao@gmail.com> writes:
> > >
> > > As we can see from above information that the physical memory in system
> > > is 32768MB(32GB). However OS is only using about
> > > (32768-512)MB(MemTotal: 33010240 kB). Does this mean that this
> > > linux kernel can't use the physical memory remapped
> > > from (4G-512M, 4G) to (32G, 32G+512M)?
> >
> > The linux kernel can only use the memory passed to it by the BIOS.
> > Sometimes they need special BIOS setup options to enable remapping. If
> > there are no such options and you can't upgrade it you're out of luck
>
> Yes, I have enabled mem hole remapping in BIOS SETUP.
> After looking into dmesg, I found that all 32GB physical memory has
> been allocated to 8 nodes, but why MemTotal shows a less amount of
> memory than 32GB? Interesting......

There is some loss of memory before MemTotal, both from the BIOS
(SMM, Frame Buffer for integrated graphics etc.) and from the kernel
(mem_map which costs a few percent and some other data structures
which are allocated early)

I covered this in detail in http://halobates.de/memorywaste.pdf

> Does MemTotal means the amount of physical memory allocated to all
> nodes? Or it has different meanings?

Amount of memory left over after early boot on all nodes and visible
to the kernel (so e.g. minus reservations for kdump kernels)

-Andi


\
 
 \ /
  Last update: 2008-04-09 11:11    [W:0.077 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site