Memory residence

Mon May 23 08:12:00 GMT 2005

Generally speaking, AOT compilers like GCJ are known to be
advantageous to JVMs which interpret and/or compile Java bytecode.
I observed memory occupation of Java programs with GCJ 4.0, gij and
JDK 5.0 on a Linux box.
The first Java program is very simple one which just pauses for 60 sec:
 public class Pause {
 public static void main(String[] args) {
 try { Thread.sleep(60000); } catch (InterruptedException e) {}
 }
 }
Memory occupation of the program (and a runtime) shown by 'ps' command
is as follows:
 [gcj -O2]
 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
 shudo 22322 5.0 2.4 34512 12560 pts/6 Sl+ 05:07 0:00 ./Pause
 [gij]
 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
 shudo 22329 4.0 2.0 37580 10640 pts/6 Sl+ 05:07 0:00 gij Pause
 [JDK 1.5.0_03]
 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
 shudo 22246 1.8 1.9 262316 9848 pts/6 Sl+ 05:05 0:00 java Pause
JDK 1.5 showed the least number in RSS.
Another Java program is Eclipse, an IDE. The version runs with JDK 5.0
is 3.1M7 and one with GCJ is 3.1M6 I found in the current development
version of Fedora Core 4. Initial heap size was set as 40 MB in all cases.
 [GCJ]
 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
 shudo 22108 85.8 27.0 298872 139488 pts/5 Sl+ 05:00 0:19 ...
 [JDK 1.5.0_03]
 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
 shudo 21990 23.5 16.3 511188 84068 pts/5 Sl+ 04:57 0:08 ...
JDK 1.5 showed less number then GCJ in RSS again.
Today, we cannot claim that GCJ is superior to usual JVMs in memory
consumption. Is this correct? Could GCJ be improved?
 Kazuyuki Shudo
 Grid Technology Research Center
 National Institute of Advanced Industrial Science and Technology (AIST)