Mailing List Archive

On Fri, Jun 24, 2005 at 11:13:26AM -0700, DMZ LEISHANGTHEM wrote:
> 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?

4GB of RAM may be the maximum your kernel got - assuming its a x86,
you may need special code to support more than 4GB of RAM.

So, as Xen manages your RAM, and it seems like it does not support
more than 4gb (does anyone else :) ?), you should contact some
xen-developers asking for support, and wait for the next release.

>
> thanks
> dmz.
>
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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.

James

DMZ LEISHANGTHEM wrote:
> 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?
>
> thanks
> dmz.
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users

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