[Xen-devel] Synchronous scrubbing for alloc_domheap_pages()

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

I'm running into an issue where alloc_domheap_pages() fails, even
though there is free memory, because the memory hasn't been scrubbed
yet.  The context of this is when ballooning down one VM in order to
start a second VM: the balloon driver on the first VM has reached its
target, but creation of the second VM fails because the freed memory
hasn't been scrubbed yet.

In the situation where there is no memory on the free list, but memory
on the "to-be-srubbed" list, is there any reason why we don't do
syncronous scrubbing?

The alternative would be to teach the control tools to look at
unscrubbed vs free memory, and wait until there was enough to start
the VM; but that seems a bit more hackish.

I chatted with Tim Deegan about this, and the only issue he could see
would be making sure that hypercalls which called
alloc_domheap_pages() yielded reasonably.

Thoughts?
 -George

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