Re: [Xen-devel] balloon question

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 8 Jun 2006, at 14:51, Jan Beulich wrote:

> Running with Xen option dom0_mem=6G and kernel option mem=8G, I would 
> have expected that I would see the system with a
> 2G balloon right after boot. However, the balloon is empty. Briefly 
> looking at this, it would seem to me that, with all
> pages being reserved when the system starts and only the populated 
> ones getting the reserved status cleared in
> __free_pages_bootmem(), the condition to put pages into the balloon in 
> balloon_init() is inverted.
i386 deliberately marks pages beyond start_info->nr_pages as not 
Reserved so they get picked up by the balloon driver. Either x86/64 
needs to do the same, or we stop doing that in i386. But then there 
will be pages that are legitimately Reserved that the balloon driver 
will erroneously pick up. Or we could make the balloon driver 
explicitly pick up all pages from start_info->nr_pages. Or have an 
interface to allow arch code to register page ranges with the balloon 
driver. This needs a little thought....
> Also, dying in xen_destroy_contiguous_region() (and similarly in the 
> failure recovery code in
> xen_create_contiguous_region()) if the space just unmapped can't be 
> re-populated seems overly harsh (we're having a case
> where this actually happens); wouldn't it make sense to make this 
> fatal only when the page can't be replaced by a free
> one (allocated inside the domain, with the page stolen for this then 
> simply pushed into the balloon, similar to
> balloon_alloc_empty_page_range() except without freeing the memory to 
> Xen)?
As it happens I'm fixing this exact problem right now. :-) Expect a fix 
in -unstable and -testing in the next few days.
 -- Keir


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