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Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature
- To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
- Date: Mon, 5 Nov 2012 17:14:17 +0000
- Cc: "Tim \(Xen.org\)" <tim@xxxxxxx>, Olaf Hering <olaf@xxxxxxxxx>, "Keir \(Xen.org\)" <keir@xxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Konrad Wilk <konrad.wilk@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, George Shuklin <george.shuklin@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxx>, DarioFaggioli <raistlin@xxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Kurt Hackel <kurt.hackel@xxxxxxxxxx>, Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>
- Delivery-date: Mon, 05 Nov 2012 17:14:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xen.org>
On 30/10/12 15:43, Dan Magenheimer wrote:
a) Truly free memory (each free page is on the hypervisor free list)
b) Freeable memory ("ephmeral" memory managed by tmem)
c) Owned memory (pages allocated by the hypervisor or for a domain)
The sum of these three is always a constant: The total number of
RAM pages in the system. However, when tmem is active, the values
of all _three_ of these change constantly. So if at the start of a
domain launch, the sum of free+freeable exceeds the intended size
of the domain, the domain allocation/launch can start.
Why free+freeable, rather than just "free"?
But then
if "owned" increases enough, there may no longer be enough memory
and the domain launch will fail.
Again, "owned" would not increase at all if the guest weren't handing
memory back to Xen. Why is that necessary, or even helpful?
(And please don't start another rant about the bold new world of peace
and love. Give me a freaking *technical* answer.)
-George
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