Fedora xen - Aug 2007 - freeing up memory back to Domain-0

How can you free up memory when you shut a guest down?  Give back to
Domain-0 so you can start another one up?

Also, were are the profiles for xen stored?  For example I create all of
them under /vm/xen/blah if I decide to delete blah1 and create a new one
named blah1 it says it is already there, even though I removed it.

Justin Conover wrote:

[These are a couple of frequently asked questions ... do we have an FAQ?]
> How can you free up memory when you shut a guest down?  Give back to 
> Domain-0 so you can start another one up?
Domain-0 doesn''t recover the memory when a domain shuts down.  The 
assumption (within Xen) is that another domain will be starting up 
shortly, so there is no point wasting time returning the memory to Domain-0.

However the memory hasn''t just gone away, as your question implies. 
The
hypervisor is still managing that free memory, and will give it to the 
next guest which starts up.

If you really want to give the free memory back to Domain-0, then I 
think you can do it by:

   virsh setmem Domain-0 <kb>

where <kb> is the total number of kilobytes that you want Domain-0 to 
have (ie. current size + size of freed guest -- you have to calculate 
this for yourself).
> Also, were are the profiles for xen stored?  For example I create all of 
> them under /vm/xen/blah if I decide to delete blah1 and create a new one 
> named blah1 it says it is already there, even though I removed it.
Since Xen 3.0.3 or 3.0.4, I forget exactly which, Xen manages the 
profiles in its own private place.  So there are no configuration files. 
  I agree that this is very annoying, but that''s the way Xen forces us 
to do it.

To view or edit a configuration file, you now have to do:

   virsh dumpxml domain > domain.xml
   edit domain.xml
   virsh define domain.xml

(''virsh define'' only works if the domain has been shutdown, so
if it is
still running then shut it down first using ''virsh shutdown'').

If you want to make a change to a running domain, there are some changes 
which you are allowed to do, basically adding and removing block and 
network devices, and adding and removing memory.  The commands to use are:

   virsh attach-device
   virsh attach-disk
   virsh attach-interface
   virsh detach-device
   virsh detach-disk
   virsh detach-interface
   virsh setmem
   virsh setmaxmem

(Just do ''virsh help command'' to get help on each of those
commands).

Rich.

-- 
Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/
Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod
Street, Windsor, Berkshire, SL4 1TE, United Kingdom.  Registered in
England and Wales under Company Registration No. 03798903

Richard W.M. Jones wrote:
> Justin Conover wrote:
>> Also, were are the profiles for xen stored?  For example I create all 
>> of them under /vm/xen/blah if I decide to delete blah1 and create a 
>> new one named blah1 it says it is already there, even though I removed 
>> it.
I should add that if you want Xen to completely forget about a domain, 
you must:

  (1) shut it down, if not already (virsh shutdown)
  (2) undefine it (virsh undefine)
  (3) delete any disk image file or disk partition

It''s step (3) which actually gets rid of the data stored in the domain.

Rich.

-- 
Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/
Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod
Street, Windsor, Berkshire, SL4 1TE, United Kingdom.  Registered in
England and Wales under Company Registration No. 03798903

On 8/21/07, Richard W.M. Jones <rjones@redhat.com>
wrote:
>
> Justin Conover wrote:
>
> [These are a couple of frequently asked questions ... do we have an FAQ?]
>
> > How can you free up memory when you shut a guest down?  Give back to
> > Domain-0 so you can start another one up?
>
> Domain-0 doesn''t recover the memory when a domain shuts down.  The
> assumption (within Xen) is that another domain will be starting up
> shortly, so there is no point wasting time returning the memory to
> Domain-0.
>
> However the memory hasn''t just gone away, as your question
implies.  The
> hypervisor is still managing that free memory, and will give it to the
> next guest which starts up.
>
> If you really want to give the free memory back to Domain-0, then I
> think you can do it by:
>
>    virsh setmem Domain-0 <kb>
>
> where <kb> is the total number of kilobytes that you want Domain-0 to
> have (ie. current size + size of freed guest -- you have to calculate
> this for yourself).
>
> > Also, were are the profiles for xen stored?  For example I create all
of
> > them under /vm/xen/blah if I decide to delete blah1 and create a new
one
> > named blah1 it says it is already there, even though I removed it.
>
> Since Xen 3.0.3 or 3.0.4, I forget exactly which, Xen manages the
> profiles in its own private place.  So there are no configuration files.
>   I agree that this is very annoying, but that''s the way Xen
forces us
> to do it.
>
> To view or edit a configuration file, you now have to do:
>
>    virsh dumpxml domain > domain.xml
>    edit domain.xml
>    virsh define domain.xml
>
> (''virsh define'' only works if the domain has been
shutdown, so if it is
> still running then shut it down first using ''virsh
shutdown'').
>
> If you want to make a change to a running domain, there are some changes
> which you are allowed to do, basically adding and removing block and
> network devices, and adding and removing memory.  The commands to use are:
>
>    virsh attach-device
>    virsh attach-disk
>    virsh attach-interface
>    virsh detach-device
>    virsh detach-disk
>    virsh detach-interface
>    virsh setmem
>    virsh setmaxmem
>
> (Just do ''virsh help command'' to get help on each of
those commands).
>
> Rich.
>
> --
> Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/
> Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod
> Street, Windsor, Berkshire, SL4 1TE, United Kingdom.  Registered in
> England and Wales under Company Registration No. 03798903
>
>
Very nice, thank you.