>>>>> "ag" == Andrew Gabriel <andrew.gabr...@sun.com> writes:
ag> is your working set size bigger than memory (thrashing),
n...no, not...not exactly. :)
ag> or is swapping likely to be just a once-off event or
ag> infrequently repeated?
once-off! or...well...repeated, every time the garbage collector runs.
ag> You probably need to forget most of what you learned about
ag> swapping 25 years ago, when systems routinely swapped, and
ag> technology was very different.
yes, some Lisp machines had integrated swapper/garbagecollectors. Now
we have sbrk() + gc. dumb!
We used to not worry about overcommitting because refusing to
overcommit just meant some of the allocated swap space would never get
written. It was a little bit foolish because the threat of thrashing
means, whenever swap's involved, you're basically overcommitted, but
it let us feel better. Now that we're not using swap, failure to
overcommit seems rather wasteful. At the very least you should allow
the ARC cache to grow into memory reserved for an allocation, then
boot the ARC out of it if the process actually writes to more than you
thought it would and you need to keep a commitment you thought you
wouldn't.
ag> solid state disk swap devices,
smart! it might turn out to be good for ebooks and other
power-constrained devices, too, because DRAM uses battery: swapping to
conserve energy rather than RAM. It might be worth tracking pages in
a more complicated way than we're now doing if the goal is to evacuate
RAM and power it down, so maybe holding onto ancient swap wisdom and
code isn't as helpful to this as it might seem.
The point, keep swap on ZFS so you can grow/shrink/delete it as
fashion changes, is good. But the OP's question still stands: does
ZFS swap perform almost as well as raw device swap, or is it worth
partitioning disks if you insist on actually using swap? I guess no
one knows.
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