Re: [Xen-devel] [PATCH] Fix e820 mapping limit

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Tue, Dec 12, 2006 at 06:25:25PM +0000, Daniel P. Berrange wrote:
> The changeset '12803:df5fa63490f4da7b65c56087a68783dbcb7944f8' added a new
> hypercall XENMEM_set_memory_map for specifying the e820 mapping. There was
> a small bug in the userspace side of this change though - the e820 mapping
> was specified based on the 'memory_static_min' domain info parameter which
> means the memory map size is clamped to the value 'memory' config option.
> 
> What we actually want is to setup the e820 map limit based on 'maxmem'
> config option, so that we can balloon up the guest to its max limit.
> 
>  eg
>   If we boot with 'memory=400' and 'maxmem=800', the e820 map should be
>   set to 800 MB, and the guest should allocate  only 400 MB at startup.
>   It should then be possible to use 'xm mem-set' after boot to assgin
>   upto this 800 MB.
> 
> Thus, the attached patch fixed the image.py class to setup the e820 mapping
> based on 'memory_static_max' which is in turn based on 'maxmem'. Booting
> with this patch I can verify that the guest kernel sees a 800 MB e820 map,
> so this fixes the initial problem.
> 
> There appears to be a second issue somewhere in the stack though, because
> even if do 'xm mem-set <domid> 600', while the ballon driver in the guest
> will see the 600 MB target, it will still never try to allocate its 
> increased target.

Turns out this was a bug introduced in the refactoring of memory config
parameters from Xen API work. The memory & memmax parameters were getting
initialized the wrong way around. With this fixed & the e820 map fix, 
memory ballooning works perfectly:

  # xm create demo
  Using config file "/etc/xen/demo".
  Going to boot Fedora Core (2.6.18-1.2769.2.2.el5xen)
    kernel: /vmlinuz-2.6.18-1.2769.2.2.el5xen
    initrd: /initrd-2.6.18-1.2769.2.2.el5xen.img
  Started domain demo
  # xm list demo
  Name                                      ID   Mem VCPUs      State   Time(s)
  demo                                      16   410     2     -b----      0.4
  # xm mem-set demo 600
  # xm list demo
  Name                                      ID   Mem VCPUs      State   Time(s)
  demo                                      16   600     2     -b----      4.2


Attaching an updated patch which fixes both the memory ballooning issues
in one go

  Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx>

Regards,
Dan.
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Attachment: xen-mem-e820-size-2.patch
Description: Text document

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