Joel VanderWerf
3/29/2006 6:43:00 AM
John Carter wrote:
> Some old Pascal implementations had (and I think some still do) had a
> facility to "mark" the heap, and then at some point "release" all
> items allocated after that mark.
>
> Here is a nifty way of doing the same (and more!) in ruby....
>
> ==========================try.rb======================================
> pid = Process.fork do
> # Load any modules we need
> require 'find'
>
> a = 'x' * 100*1024*1024
>
>
> end
>
> pid, result = Process.waitpid2( pid)
> ======================================================================
If possible, disable GC in the fork. That can greatly reduce memory
usage because the GC mark algorithm has to touch every reachable block
of allocated heap memory. So the memory manager has to copy most of the
original process anyway--the COW advantage is lost. This is especially
true if the parent process has a lot of objects. Example:
a = (1..2_000_000).map {[]} # emulate a big ObjectSpace
10.times do
pid = fork do
GC.disable if ARGV[0] == "nogc"
a = 'x' * 10*1024*1024 # trigger GC, if enabled
puts `free`[/Swap.*/]
end
end
Process.waitall
$ time ruby fork-gc.rb nogc
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
Swap: 489940 137340 352600
ruby fork-gc.rb nogc 5.29s user 0.62s system 97% cpu 6.049 total
$ time ruby fork-gc.rb
Swap: 489940 326976 162964
Swap: 489940 327100 162840
Swap: 489940 327336 162604
Swap: 489940 330228 159712
Swap: 489940 334664 155276
Swap: 489940 330456 159484
Swap: 489940 329060 160880
Swap: 489940 328124 161816
Swap: 489940 327148 162792
Swap: 489940 327072 162868
ruby fork-gc.rb 8.82s user 2.97s system 28% cpu 40.712 total
Note the big increase in swap used (second column of numbers).
** Caution: on my 512MB system this can thrash for a while. If you have
less memory, change the parameters.
--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407