Re: [Xen-devel] big memory and balloons

[Bin Ren <br260@xxxxxxxxx>]

On 16 Feb 2004, at 15:20, David Becker wrote:

> I want to put Xen on some 2GB hosts and am exploring the balloon
> mechansism.  If I try to inflate the balloon more than 32768 pages at a
> time, the guest OS gets an oops:
>   Unable to handle kernel NULL pointer dereference at virtual address 
> 00000000
> Deflating the balloon crashes the guest:
>   <1>bd240 debug: deflate balloon called for fa0 pages
>   Kernel panic: Failed mmu update: c019a3c0, 2048
Currently Xen doesn't fully support (some basic support exists) HIGHMEM.
As a result, each XenoLinux can at most have 896-64=832M memory.

Besides, it has been quite a long time that no one has ever laid a 
finger on
'balloon' tool. It's very likely broken, thus not a good start point 
for you to
play with Xen & XenoLinux.

> Xen and DOM0 keep on running fine :-)
>
> Is deflation required?  Or does Xen hand out pages on demand as guests
> need them?
Deflation is not required. You give the memory you want to allocate for 
a
particular domain and Xen will try to get all the page frames (i.e. 
real machine
memory pages) reserved for this domain. Then it's domain's own 
responsibility
to use the allocated memory properly.

> Is the linux config setting HIGHMEM4G supported?  If not, can Xen 
> itself
> see all 2GB and hand out independent 800MB chunks to guests
Currently not supported but not too much too add, mainly involving 
modification
to the domain building process.

-- Bin



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