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Subject: Re: [PATCH V3] xen/balloon: Memory hotplug support for Xen balloon
 driver
From: Ian Campbell <Ian.Campbell@eu.citrix.com>
To: "v.tolstov@selfip.ru" <v.tolstov@selfip.ru>
CC: Daniel Kiper <dkiper@net-space.pl>,
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Organization: Citrix Systems, Inc.
Date: Wed, 18 May 2011 08:21:49 +0100
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On Wed, 2011-05-18 at 07:57 +0100, Vasiliy G Tolstov wrote:
> On Tue, 2011-05-17 at 23:44 +0200, Daniel Kiper wrote:
> > +	  Memory could be hotplugged in following steps:
> > +
> > +	    1) dom0: xl mem-max <domU> <maxmem>
> > +	       where <maxmem> is >= requested memory size,
> > +
> > +	    2) dom0: xl mem-set <domU> <memory>
> > +	       where <memory> is requested memory size; alternatively memory
> > +	       could be added by writing proper value to
> > +	       /sys/devices/system/xen_memory/xen_memory0/target or
> > +	       /sys/devices/system/xen_memory/xen_memory0/target_kb on dumU,
> > +
> > +	    3) domU: for i in /sys/devices/system/memory/memory*/state; do \
> > +	               [ "`cat "$i"`" = offline ] && echo online > "$i"; done
> > +

> Very good. Is that possible to eliminate step 3 ? And do it automatic if
> domU runs with specific xen balloon param?

When we faced the same question WRT VCPU hotplug we ended up using a
udev rule. Presumably the same could be done here. In the VCPU case the
rule is:

ACTION=="add", SUBSYSTEM=="cpu", RUN+="/bin/sh -c '[ ! -e /sys$devpath/online ] || echo 1 > /sys$devpath/online'"

Presumably the memory one will be broadly similar.

Ian.

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