Re: [PATCH 1 of 2] Global virq for low memory situations

["Andres Lagar-Cavilla" <andres@lagarcavilla.org>]

>> From: Andres Lagar-Cavilla [mailto:andres@lagarcavilla.org]
>> Sent: Wednesday, February 29, 2012 7:26 PM
>> To: xen-devel@lists.xensource.com
>> Cc: ian.campbell@citrix.com; andres@gridcentric.ca; tim@xen.org;
>> JBeulich@suse.com;
>> ian.jackson@citrix.com; adin@gridcentric.ca
>> Subject: [Xen-devel] [PATCH 1 of 2] Global virq for low memory
>> situations
>>
>>  xen/common/page_alloc.c  |  112
>> +++++++++++++++++++++++++++++++++++++++++++++++
>>  xen/include/public/xen.h |    1 +
>>  2 files changed, 113 insertions(+), 0 deletions(-)
>
> Just a note that I think this will trigger false positives when
> Xen tmem is working (with tmem-enabled guests).  With tmem,
> Xen has two classes of free memory: free and "freeable".
> In many situations, free will approach 0 but there will still
> be lots of "freeable" memory which is available for guest
> ballooning, launching new domains, etc.
>
> It may be the case that your virq may never be used on
> a system with a tmem guest, but if it is, weird things
> (like unnecessary hypervisor swapping) may happen.

Since I know zero point zero zero zip nada about tmem, maybe the most
efficient path is that you throw on top of the patch the tmem magic. Which
would seem to be all about factoring tmem_freeable_pages() into the
calculation?

Thanks,
Andres
>
> Dan
>