# Optimization tweak . Using fork as a "mark" and "release" he **URL:** \ **Category:** Ruby\ **Created:** [March 29, 2006, 4:48am UTC](https://www.ruby-forum.com/t/optimization-tweak-using-fork-as-a-mark-and-release-he/56215 "2006-03-29T04:48:48Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![amin1426](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/4da419/32.png) [@amin1426](https://www.ruby-forum.com/u/amin1426)\ **Post date:** [March 29, 2006, 4:48am UTC](https://www.ruby-forum.com/t/optimization-tweak-using-fork-as-a-mark-and-release-he/56215/1 "2006-03-29T04:48:48Z")
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) Here is an edited version of the result of running (from root) strace -v -f -o strace.log ruby try.rb ====================================================================== 1597 execve("/usr/local/bin/ruby", [“ruby”, “try.rb”], [“HZ=100”, “SHELL=/bin/bash”, “TERM=xterm”, “OLDPWD=/root”, “USER=root”, “MAIL=/var/mail/root”, “PATH=/usr/local/sbin:/usr/local/”…, “PWD=/home/johnc/tmp”, "PS1=\h:\w\$ ", “SHLVL=1”, “HOME=/root”, “LOGNAME=root”, “DISPLAY=:0.0”, “\_=/usr/bin/strace”]) = 0 …all the start up cost of invoking ruby paid once and only once… Here is the OS level call to fork… 1597 clone(child\_stack=0, flags=CLONE\_CHILD\_CLEARTID|CLONE\_CHILD\_SETTID|SIGCHLD, child\_tidptr=0xb7d57708) = 1598 # Note this is really really very fast as unix just creates a complete # copy via COW pages (copy on write) using virtual memory magic. # Parent proc hands waiting for child… 1597 waitpid(1598, \ # Child proc loads and evals find.rb 1598 open("/usr/local/lib/ruby/1.9/find.rb", O\_RDONLY|O\_LARGEFILE) = 3 1598 close(3) = 0 1598 open("/usr/local/lib/ruby/1.9/find.rb", O\_RDONLY|O\_LARGEFILE) = 3 1598 ioctl(3, SNDCTL\_TMR\_TIMEBASE or TCGETS, 0xbfd1baa8) = -1 ENOTTY (Inappropriate ioctl for device) 1598 read(3, “#\n# find.rb: the Find module for”…, 8192) = 1922 # Child proc grabs a huge chunk more memory 1598 brk(0x81c1000) = 0x81c1000 1598 mmap2(NULL, 104861696, PROT\_READ|PROT\_WRITE, MAP\_PRIVATE|MAP\_ANONYMOUS, -1, 0) = 0xb1925000 # Child exits… 1598 exit\_group(0) = ? 1597 \<… waitpid resumed\> [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0) = 1598 1597 — SIGCHLD (Child exited) @ 0 (0) — # WHEE! Bang! All the memory and resources associated with the child # are reclaimed completely and instantly by the OS. # parent continues on it merry way light and free… John C. Phone : (64)(3) 358 6639 Tait Electronics Fax : (64)(3) 359 4632 PO Box 1645 Christchurch Email : removed\_email\_address@domain.invalid New Zealand Carter’s Clarification of Murphy’s Law. “Things only ever go right so that they may go more spectacularly wrong later.” From this principle, all of life and physics may be deduced. ---
**Author:** ![amin1426](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/4da419/32.png) [@amin1426](https://www.ruby-forum.com/u/amin1426)\ **Post date:** [March 29, 2006, 5:28am UTC](https://www.ruby-forum.com/t/optimization-tweak-using-fork-as-a-mark-and-release-he/56215/2 "2006-03-29T05:28:05Z")
On Wed, 29 Mar 2006, John C. wrote: > a = ‘x’ \* 100_1024_1024 > > end > > # pid, result = Process.waitpid2( pid) you can get an object back from the child using: ``` harp:~ > cat a.rb def child r, w = IO.pipe IO.popen('-') do |pipe| if pipe w.close buf = pipe.read pipe.close raise Marshal.load(r.read) unless $? == 0 Marshal.load(buf) else r.close begin print(Marshal.dump(yield)) rescue Exception => e w.print(Marshal.dump(e)) exit! 42 end end end ensure r.close end emsg = lambda{|e| STDERR.puts %Q[#{ e.message } (#{ e.class })\n#{ ``` e.backtrace.join “\n” }]} ``` p child{ 'value from child' } rescue emsg[$!] p child{ error_from_child } rescue emsg[$!] p 'but the parent lives' harp:~ > ruby a.rb "value from child" undefined local variable or method `error_from_child' for ``` main:Object (NameError) a.rb:29 a.rb:14:in `child' a.rb:4:in`child’ a.rb:29 “but the parent lives” with all the same memory preserving side effects. regards. -a ---
**Author:** ![amin1426](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/4da419/32.png) [@amin1426](https://www.ruby-forum.com/u/amin1426)\ **Post date:** [March 29, 2006, 8:43am UTC](https://www.ruby-forum.com/t/optimization-tweak-using-fork-as-a-mark-and-release-he/56215/3 "2006-03-29T08:43:02Z")
John C. wrote: > 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.