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

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Andres Lagar-Cavilla [mailto:andres@xxxxxxxxxxxxxxxx]
> Sent: Wednesday, February 29, 2012 7:26 PM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: ian.campbell@xxxxxxxxxx; andres@xxxxxxxxxxxxxx; tim@xxxxxxx; 
> JBeulich@xxxxxxxx;
> ian.jackson@xxxxxxxxxx; adin@xxxxxxxxxxxxxx
> 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.

Dan

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