> I have been making use of copy-on-write semantics of linux fork to
> duplicate a process around 100+ times to generate client load against a
> server. The copy-on-write allows me to run many more processes without
> swap thrashing than I'd otherwise be able to. The client code is in
> perl, so the process sizes are in the MBs. Using this technique I only
> need about 2 MB per user, with around 5.5 MB shared.
[snip COW undone on swapout, leading to thrashing]
> Is this expected and reasonable behaviour?
Absolutely not, this is not supposed to happen.
> Is it possible for pages to remain shared, even when they are swapped
> to disk?
I think this already happens in the -ac kernels, probably
in -linus too (though I'm not 100% sure).
> Does that already happen anyway, meaning my analysis of the situation
> is off base?
Possible, but it's also possible you ran into a real bug,
it would be interesting to debug this further...
I wouldn't rule out a bug with the remove-from-swapcache
logic on swapin, either.
regards,
Rik
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