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Re: [Xen-users] memory question!

To: DMZ LEISHANGTHEM <dmz_leishangthem@xxxxxxxxx>
Subject: Re: [Xen-users] memory question!
From: James Bulpin <James.Bulpin@xxxxxxxxxxxx>
Date: Sat, 25 Jun 2005 10:53:59 +0100
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There are two things here:

1 - support for greater than 4GB of physical RAM. This needs PAE support which isn't in the Xen 2.0 series. This will be in 3.0 which will be out this summer.

2 - missing memory between 3 and 4GB (your scenario has 3GB already allocated and you cannot allocate a further 512MB). I ran into this myself recently too. I'm told that it is to do with the BIOS remapping regions of memory away from areas of address space used by memory-mapped devices (this memory would otherwise be unaddressable and wasted). For machines with less than 4GB this isn't a problem for Xen because the remapping would be to addresses below 4GB. If you have 4GB then it ends up being remapped above 4GB. In this case, you need PAE to get to it.

Run 'xm info', you'll probably see about 3300MB total memory available.


I have a question about memory. I have 8GB of RAM on a
Dell PE 1850(usb disabled kernel, cos it gets locked
up on heavy I/O). My domain0 has only 2 gigs of
memory. I have 2 guest domains 512 each. Now when i
try to create a 3rd guest domain of 512, xen wont let
me do it. My confusion is "Is 4G the max amount of
memory a domain can  get/ or is 4G the max amout of
cumulative memory all the domains can get(ie. dom0,
dom1, dom2... etc..combined all together)."
can i have my domain0 have 4G ram, and at the same
time domain1 have 4 G of ram?


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