This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


[Xen-devel] Re: [PATCH] GSoC 2010 - Memory hotplug support for Xen guest

On Wed, 25 Aug 2010 14:33:06 -0700
Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> >> 2 requires a deeper understanding of the existing hotplug code.  It
> >> needs to be refactored so that you can use the core hotplug machinery
> >> without enabling the sysfs page-onlining mechanism, while still leaving
> >> it available for physical hotplug.  In the short term, having a boolean
> >> to disable the onlining mechanism is probably the pragmatic solution, so
> >> the balloon code can simply disable it.
> > I think that sysfs should stay intact because it contains some
> > useful information for admins. We should reconsider avaibilty
> > of /sys/devices/system/memory/probe. In physical systems it
> > is available however usage without real hotplug support
> > lead to big crash. I am not sure we should disable probe in Xen.
> > Maybe it is better to stay in sync with standard behavior.
> > Second solution is to prepare an interface (kernel option
> > or only some enable/disable functions) which give possibilty
> > to enable/disable probe interface when it is required.
> My understanding is that on systems with real physical hotplug memory,
> the process is:
>    1. you insert/enable a DIMM or whatever to make the memory
>       electrically active
>    2. the kernel notices this and generates a udev event
>    3. a usermode script sees this and, according to whatever policy it
>       wants to implement, choose to online the memory at some point
> I'm concerned that if we partially implement this but leave "online" as
> a timebomb then existing installs with hotplug scripts in place may poke
> at it - thinking they're dealing with physical hotplug - and cause problems.

IIUC, IBM guys, using LPAR?, does memory hotplug on VM.

The operation is.
        1. tell the region of memory to be added to a userland daemon.
        2. The daemon write 0xXXXXXX > /sys/devices/system/memory/probe
           (This notifies that memory is added physically.)
           Here, memory is created.
        3. Then, online memory.

I think VM guys can use similar method rather than simulating phyiscal hotplug.
Then, you don't have to worry about udev etc...
No ?


Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>