>>>>> "bf" == Bob Friesenhahn <[EMAIL PROTECTED]> writes:
bf> What is the relationship between the size of the memory
bf> reservation and thrashing?
The problem is that size-capping is the only control we have over
thrashing right now. Maybe there are better ways to predict thrashing
than through reservation size, and maybe it's possible to design swap
admission control that's safer and yet also more gracious to your
Java-like reservations of large cold datasets than the flat capping we
have now, but Mac OS doesn't have it.
I suspect there are even <cough> some programs that try to get an idea
how much memory pressure there is, and how often they need to gc, by
making big reservations until they get ENOMEM. They develop tricks in
an ecosystem, presuming some reasonable swap cap is configured, so
removing it will mess up their (admittedly clumsy) tricks.
To my view, if the goal is ``manual tuning is bad. we want to
eliminate swap size as a manual tuneable,'' then the ``dynamic''
aspect of the tuning should be to grow the swap area until it gets too
hot: until the ``demand'' is excessive. Some WFQ-ish thing might be
in order, too, like a complicated version of ulimit. But this may be
tricky or impossible, and in any case none of that is on the table so
far: the type of autotuning you are trying to copy from other
operating systems is just to remove the upper limit on swap size
entirely, which is a step backwards.
I think it's the wrong choice for a desktop, but it is somewhat
workable choice on a single-user machine where it's often just as
irritating to the user if his one big application crashes in which all
his work is stored, as if the whole machine grinds to a halt. But
that view is completely incompatible with most Solaris systems as well
as with this fault-isolation, resiliency marketing push with sol10.
so, if you are saying Mac users are happy with dynamic swap, <raises
hand>, not happy!, and even if I were it's not applicable to Solaris.
I think ZFS swap should stay with a fixed-sized (albeit manually
changeable!) cap until Java wizards can integrate some dynamicly
self-disciplining swap concepts into their gc algorithms (meaning,
probably forever).
bf> You sound angry.
Maybe I am and maybe I'm not, but wouldn't it be better not to bring
this up unless it's interfering with my ability to communicate?
Because if I were, saying I sound angry is poking the monkey through
the bars, likely to make me angrier, which is unpleasant for me and
wastes time for everyone---unless it amuses you or something. This is
a technical list. Let's not talk about our feelings, please.
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