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Re: [Xen-users] Questions on memory allocation

To: javier@xxxxxxxxxxx
Subject: Re: [Xen-users] Questions on memory allocation
From: "Ryan Burke" <burke@xxxxxxxxxxxxxxxxx>
Date: Tue, 30 Oct 2007 11:51:06 -0500 (CDT)
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Xen does not dynamically adjust the amount of memory a DomU has available.
In the configuration you've mentioned the DomU's will have 128 MB of RAM
and you can manually adjust that up to 1024 MB of RAM using the "mem-set"
command. I'm not sure if the commercial Xen products have any kind of
dynamically memory allocation but I think the problem is in the DomU
telling the Dom0 that it needs more memory. Does anyone on the list know
if there is a hypercall to notify the Dom0 if a DomU is low on free


> Hi all,
>    I'm trying to tune some memory parameters in my dom0 and domUs, and got
> stuck. I've been googling, but can't find something "straightforward" ;)
>    I have a dom0 with 2GB RAM, and have 5 domUs in it, using Xen 3.1.0
> with
> kernel 2.6.18, all installed through Debian packages.
>    My dom0 is launched with
> xenhopt=dom0_mem=256MB
>    in grub's /boot/grub/menu.lst.
>    I've created all my domUs with the following memory parameters:
> ----
> memory  = '128'
> maxmem  = '1024'
> shadow_memory = 8
> ----
>    My domUs have a swap partition, and I've setted the kernel's swappiness
> to 0.
>    With this config, I understand that the domUs will be started with an
> starting amount of 128 MB RAM, and they will grow the amount used
> according to their needs and availability. Well. No. They begin swapping
> :/
>    In one domU, that is using almost all the initial memory, when
> disabling
> the swap and launching another process, the OOM killer start killing
> processes.
>    I've read something about a "balloon driver" that should do the magic,
> but it all refers to info prior to 2006. In a chat script someone said
> that it is now handled with the "mem-set/mem-max" parameters. There was
> also some other guy telling about /proc/xen/balloon, but couldn't find any
> detailed info on that either.
>    By now, I'm suspicious that I've missunderstood the memory handling in
> Xen :)
>    Can you tell me if xen dom0/domUs CAN really dynamically allocate
> memory
> to the domUs on demand? If so, is there any documentation I can read to
> config it properly? do I need to run any application in the domXs?
>    Any help, any lead, any clue, will be greatly appreciated :)))))
>    Thanks in advance
>                  Javier, a.a.t.
> --
>     "The Universe we observe has precisely the properties we should
>   expect if there is, at bottom, no design, no purpouse, no evil, no
>   good, nothing but blind, pitiless indiference."
>                                                         (Richard Dawkins)
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