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xen-devel
Re: [Xen-devel] questions about ballooning
On Sun, 2007-11-04 at 15:04 +0000, Steve Kemp wrote:
> I have been confused about ballooning on dom0 for a while, so
> this looks like a good time to ask it.
>
> I have dom0 with ~1Gb of memory. (About 900Mb as shown in 'xm list'
> once it is freshly booted.)
>
> I start a guest, and that gets decreased as the memory is allocated
> to domU:
>
> Name ID Mem
> Domain-0 0 735
> etch32-builder.my.flat 24 128
>
> After a while I shutdown that guest and I expect the memory to
> be available to dom0 again - but it never is. I see dom0 left
> with the reduced ~700Mb.
>
> Is that expected?
a leak of that size would not go unnoticed :)
outline, but no warranties, as i didn't build it:
- in the beginng, .. well, all memory belongs to xen.
- dom0, unless otherwise configured (mem=), gets a map of up to the
whole amount of memory. so anything beyond the VMM can be in dom0.
- lacking any other domain beyond dom0 on boot, the initial reservation
of dom0 is filled with all pages beyond the VMM allocation. 900MB.
- creating a domU requires dom0 to return part of its
reservation (decrease_reservation()). 128MB.
- destroying domU is up to the VMM. these pages are not automagically
reclaimed by dom0. there is also to 'pushing' of pages in a domain,
as there is no point in doing so. dom0 needs to ask (via
increase_reservation()).
- dom0, rather idle, is as happy with 735MB as it used to be with
900MB.
so the freed domU memory stays on the xen heap for the time being.
regards,
daniel
--
Daniel Stodden
LRR - Lehrstuhl für Rechnertechnik und Rechnerorganisation
Institut für Informatik der TU München D-85748 Garching
http://www.lrr.in.tum.de/~stodden mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33 3D80 457E 82AE B0D8 735B
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