[Xen-devel] Time to increase default dom0_mem value?

[Jared Rhine <jared@xxxxxxxxxxx>]

  Jared> [P]erhaps [...] a dom0_mem of 16Mb [is] not a good default
  Jared> value?

  Keir> Sensible defaults are probably either a fixed proportion of
  Keir> total system RAM, or just to print an error and hang. Either
  Keir> of these is easy to implement.

Given only those two choices, I definitely think that "require
dom0_mem to be set otherwise error out" is the preferred choice.

Using a percentage of total RAM seems error-prone and will cause even
more community problems because of different behaviors on different
machines.  (In other words, you'll now need to ask not only "what did
you set dom0_mem to?", but also "how much total is available?").  If
the default is say 25%, then a 64Mb machine is right back to the
problematic 16Mb, while a 2Gb machine would reserve an unneeded
half-a-gig.  Correctness and consistency should come first, so I think
the "percentage of available" approach should be rejected (though
supporting a "dom0_mem=25%" would be a reasonable enhancement).

I personally still think that having an actual value for a default
would be somewhat preferred over "dom0_mem is now a required
parameter", as that's a behavior change instead of a simple tuning.
Since all the documentation already says "dom0_mem=131072", simply
setting that to be the default would likely generate the "least
suprise" for users and work in almost all cases.

Ultimately, it's strictly a matter of opinion, and the community is
unlikely to provide a clear consensus as to the "best" approach.  If a
change seems warranted based on the recurring FAQs, I'm sure the
development team will make an appropriate choice.

-- jared@xxxxxxxxxxx

"Truth is a great flirt." -- Franz Liszt


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