Xen devel - Nov 2006 - [PATCH] make ballooning up to maxmem work

Because XENMEM_maximum_reservation is rumored to change meaning in
the future, this patch adds a third amount-of-memory operation to
HYPERVISOR_memory_op() - XENMEM_maximum_memory.

This should make it possible to simply specify the maximum amount
of memory a guest will have in /etc/xen/<guest> instead of having
to pass it on the kernel commandline.

A next step would be to split out the maxmem values into two
different ones in the guest config file and the tools, but I''m
not quite sure what name to use there...

Signed-off-by: Rik van Riel <riel@redhat.com>

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>      case XENMEM_current_reservation:
>      case XENMEM_maximum_reservation:
> +    case XENMEM_maximum_memory:
>          if ( copy_from_guest(&domid, arg, 1) )
>              return -EFAULT;
This still makes use of d->max_pages in return. Isn''t it supposed to
change in the future too? IIRC, according to Keir, max_pages will track 
the _current_ number of pages, differing from tot_pages only in a brief
timeframe in which you balloon, but tot_pages was not yet updated.


-- 
Glauber de Oliveira Costa
Red Hat Inc.
"Free as in Freedom"

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On 22/11/06 10:40, "Glauber de Oliveira Costa"
<gcosta@redhat.com> wrote:
>>      case XENMEM_current_reservation:
>>      case XENMEM_maximum_reservation:
>> +    case XENMEM_maximum_memory:
>>          if ( copy_from_guest(&domid, arg, 1) )
>>              return -EFAULT;
> 
> This still makes use of d->max_pages in return. Isn''t it
supposed to
> change in the future too? IIRC, according to Keir, max_pages will track
> the _current_ number of pages, differing from tot_pages only in a brief
> timeframe in which you balloon, but tot_pages was not yet updated.
This adds a level of indirection at least, but really we may as well
implement the XENMEM_memory_map hypercall. Then there is no guest
modification required.

 -- Keir


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On Wed, Nov 22, 2006 at 11:18:39AM +0000, Keir Fraser
wrote:
> 
> 
> 
> On 22/11/06 10:40, "Glauber de Oliveira Costa"
<gcosta@redhat.com> wrote:
> 
> >>      case XENMEM_current_reservation:
> >>      case XENMEM_maximum_reservation:
> >> +    case XENMEM_maximum_memory:
> >>          if ( copy_from_guest(&domid, arg, 1) )
> >>              return -EFAULT;
> > 
> > This still makes use of d->max_pages in return. Isn''t it
supposed to
> > change in the future too? IIRC, according to Keir, max_pages will
track
> > the _current_ number of pages, differing from tot_pages only in a
brief
> > timeframe in which you balloon, but tot_pages was not yet updated.
> 
> This adds a level of indirection at least, but really we may as well
> implement the XENMEM_memory_map hypercall. Then there is no guest
> modification required.
We may need guest modifications anyway, since currently no actions are
performed if the memory_map call does not return ENOSYS. 
 

-- 
Glauber de Oliveira Costa
Red Hat Inc.
"Free as in Freedom"

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