Re: [Xen-devel] [RFH] xen domain0 failover stuff

[Don Zickus <dzickus@xxxxxxxxxx>]

On Thu, Mar 30, 2006 at 09:48:12PM -0800, Chris Wright wrote:
> * Don Zickus (dzickus@xxxxxxxxxx) wrote:
> > Continuing on my project to get a domain0 to failover to a second domain0,
> > I have stumbled upon an out of memory problem.  Does anyone know what type
> > of quirky scenario I would have had to create in order to have
> > xen_create_contiguous_region() fail within
> > swiotlb_init_with_default_size() of the linux x86_64 kernel?  
> 
> Sounds like nothing other than running low on that amount of contiguous
> pages.
> 
> CTRL-a CTRL-a CTRL-a m
> 
> Typing that should show you what's available, I suspect it's less than
> the swiotlb is asking for.

You know I have never been able to get this to work.  It keeps wanting to
initializing my modem (minicom uses the same CTRL-a interface).  :)  Or
maybe this is because I am using the redhat version.  

> 
> > I have managed to debug it down to alloc_heap_pages(MEMZONE_DMADOM, order)
> > returning NULL.  But my problem is I couldn't figure out how those heaps
> > were created in the first place.  
> 
> Boot time, IIRC.

I couldn't find any code to verify that.  From what I have seen, the heaps
are created from the act of freeing memory (I didn't see any
initialization).  So this is why I am kind of lost/stuck.  

> 
> > This domain is supposed to be configured with 256MB of memory (and "xm
> > list" confirms that).  So for the actual domain to run out of memory seems
> > illogical.  
> 
> It's the swiotlb asking for too large an order allocation.  You can
> certainly limit it to smth small like 1MB (swiotlb=1 on dom0 kernel
> command line) and hope that's sufficient.  Hmm, wonder if there would
> be a way to reuse those pages from the first dom0.
> 
> thanks,
> -chris

I tried this and no luck.  What confuses me is that normally it wants 2MB
(which isn't to big) and works fine when running multiple domUs.  I just
thought out of 256MB, there ought to be at least one 2MB chunk of contig
memory somewhere.  

Just looking for some more pointers.

Cheers,
Don


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