From: David Masover <ninja@...>
Date: 2009-11-22T05:26:33+09:00
Subject: COW-friendly Ruby 1.9?

Here's my test script:

a = []
(1024**2*10).times do
  a << Object.new
end
puts 'allocated'
gets
GC.start
puts "GC'd"
gets
GC.start unless fork
puts "GC'd and sleeping"
sleep 10

I'm using Ruby 1.9.1 from the Ubuntu Karmic repositories on x86_64.

This seems to use about 600 megs once it's allocated. (I'm un-scientifically 
watching 'free -m' to see what happens.) If I don't do the second GC, the 
forked child doesn't use much more. When I do GC in the child, or in the 
parent after the fork, it pretty much exactly doubles -- another 600 megs.

This is disappointing. After all the noise from Merb, Unicorn, Phusion, and 
"enterprise edition", and especially considering that forking is the only real 
way to make MRI scale to multiple cores, I'd have expected some sort of COW-
friendly GC to have been merged already. Wasn't someone working on this 
somewhere back in 1.9.0?

Or is there something wrong with my benchmark? I mean, it's clearly artificial, 
and I haven't tried comparing it to the various "enterprise edition" patches.