Re: [Xen-devel] questions about ballooning

[Daniel Stodden <stodden@xxxxxxxxxx>]

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 fÃr Rechnertechnik und Rechnerorganisation
Institut fÃr Informatik der TU MÃnchen             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



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel