Re: [Xen-devel] [PATCH 08 of 10 v2] libxl: enable automatic placement of guests on NUMA nodes

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Jun 21, 2012 at 5:43 PM, Dario Faggioli <raistlin@xxxxxxxx> wrote:
>> > + *  - candidates with greater amount of free memory come first. In
>> > + *    case two (or more) candidates differ in their amount of free
>> > + *    memory by less than 10%,
>> Interesting idea -- sounds pretty reasonable.
>>
> Time will tell... :-O

The only potential concern is that it seems likely that your
comparison function above will not actually generate an ordering,
because the relationship it generates isn't transitive.  That is, you
could have a situation where A > B, B > C, but C > A.  For example:
A: freemem 1000, domains 1
B: freemem 1090, domains 2
C: freemem 1110, domains 3

In this case, A>B, because memory is within 10% but has fewer domains.
 B > C, because B is within 10%, and has fewer domains.  But C > A,
because C has more than 10% more memory than A (so its domains are not
counted against it).

 This may give you strange results from your quicksort.  But it's
likely to give something *reasonable* anyway.  (And if it turns out to
cause problems, a bubble sort shouldn't be too expensive and will
likely to be more robust against this kind of quirkiness.)

 -George

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