[Xen-devel] Re: PoD issue

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> George Dunlap <george.dunlap@xxxxxxxxxxxxx> 29.01.10 17:01 >>>
>What seems likely to me is that Xen (setting the PoD target) and the 
>balloon driver (allocating memory) have a different way of calculating 
>the amount of guest memory.  So the balloon driver thinks it's done 
>handing memory back to Xen when there are still more outstanding PoD 
>entries than there are entries in the PoD memory pool.  What balloon 
>driver are you using?

The one from our forward ported 2.6.32.x tree. I would suppose there
are no significant differences here to the one in 2.6.18, but I wonder
how precise the totalram_pages value is that the driver (also in 2.6.18)
uses to initialize bs.current_pages. Given that with PoD it is now crucial
for the guest to balloon out enough memory, using an imprecise start
value is not acceptable anymore. The question however is what more
reliable data source one could use (given that any non-exported
kernel object is out of question). And I wonder how this works reliably
for others...

>Can you let me know max_mem, target, and what the 
>balloon driver has reached before calling it quits?  (Although 13,000 
>pages is an awful lot to be off by: 54 MB...)

The balloon driver reports the expected state: target and allocation
are 1G. But yes - how did I not pay attention to this - the balloon is
*far* from being 1G in size (and in fact the difference is probably
matching quite closely those 54M).

Thanks a lot!

Jan


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