linux-kernel - Re: [PATCH V3] xen/balloon: Memory hotplug support for Xen balloon driver

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Date:	Wed, 18 May 2011 08:21:49 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	"v.tolstov@...fip.ru" <v.tolstov@...fip.ru>
CC:	Daniel Kiper <dkiper@...-space.pl>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"andi.kleen@...el.com" <andi.kleen@...el.com>,
	"haicheng.li@...ux.intel.com" <haicheng.li@...ux.intel.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"Dan Magenheimer" <dan.magenheimer@...cle.com>,
	"pasik@....fi" <pasik@....fi>,
	"dave@...ux.vnet.ibm.com" <dave@...ux.vnet.ibm.com>,
	"wdauchy@...il.com" <wdauchy@...il.com>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH V3] xen/balloon: Memory hotplug support for Xen balloon
 driver

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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