[gentoo-amd64] Re: System Memory

[Duncan]

sean posted on Tue, 01 Dec 2009 15:54:36 -0500 as excerpted:

> If I am reading this correctly my system here is not seeing all 8GB of
> memory, though the system bios does.
>
> cat /proc/meminfo
>
> MemTotal:        5581372 kB
>
> MemFree:         4051424 kB
>
> Buffers:          240436 kB
>
> Cached:           645496 kB
>
> SwapCached:            0 kB
>
>
>
> Any reason where to check why all the memory?

No time to detail ATM, but at least some of it may have to do with the 
legacy 32-bit PCI device I/O area at the top of 32-bit memory -- that is, 
at the top of the 4 gig address space.  That takes a chunk of memory 
address space, typically a half gig tho it may be a gig or so (but you 
seem to have even more missing than that??) for device io use.  If your 
bios and the kernel aren't setup properly to leave a hole in the physical 
memory address space there, the real memory addresses behind the io 
addresses will be masked and that memory not available.

Some BIOSs actually count more memory than one has when this hole is 
active, counting "thru" the hole, but displacing the real physical memory 
up above 4 gig, so 8 gig may appear as 9 or 10 gig.  Others do that, but 
then subtract the memory hole, so the total returns to normal.  Others 
may simply skip that area when detecting memory and not show it at all, 
so the memory count appears normal, even tho the hole is there.

But if you don't have that hole configured properly, you WILL lose access 
to the real memory behind it.

Gotta run...




-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman