Memory usage by Java program in LINUX machine.

[Susan Smith]

I have a Java program that I run in LINUX machine:

/usr/lib/jvm/java/bin/java -classpath .:..... -mx2m MyJavaProgram

I want to analyze the memory usage used by this program

This article (http://virtualthreads.blogspot.com/2006/02/understanding-memory-usage-on-linux.html ) recommends "pmap" to get more accurate picture [please see code snippet for result]. It mentions that I need to look at the "writeable/private" at the bottom of the result of running pmap command. I'm really confused why it is using 225,024K. Why is this?
Originally, I thought capping the heap size would help, but I don't understand why that much memory is being used.

Address           Kbytes Mode  Offset           Device    Mapping
0000000040000000      56 r-x-- 0000000000000000 0fd:00000 java
000000004010d000      12 rwx-- 000000000000d000 0fd:00000 java
0000000040110000       4 ----- 0000000040110000 000:00000   [ anon ]
0000000040111000    1024 rwx-- 0000000040111000 000:00000   [ anon ]
0000000040211000       4 ----- 0000000040211000 000:00000   [ anon ]
0000000040212000    1024 rwx-- 0000000040212000 000:00000   [ anon ]
0000000040312000       4 ----- 0000000040312000 000:00000   [ anon ]
0000000040313000    1024 rwx-- 0000000040313000 000:00000   [ anon ]
0000000040413000       4 ----- 0000000040413000 000:00000   [ anon ]
0000000040414000    1024 rwx-- 0000000040414000 000:00000   [ anon ]
0000000040514000      12 ----- 0000000040514000 000:00000   [ anon ]
0000000040517000    1016 rwx-- 0000000040517000 000:00000   [ anon ]
0000000040615000      12 ----- 0000000040615000 000:00000   [ anon ]
0000000040618000    1016 rwx-- 0000000040618000 000:00000   [ anon ]
0000000040716000      12 ----- 0000000040716000 000:00000   [ anon ]
0000000040719000    1016 rwx-- 0000000040719000 000:00000   [ anon ]
0000000040817000      12 ----- 0000000040817000 000:00000   [ anon ]
000000004081a000    1016 rwx-- 000000004081a000 000:00000   [ anon ]
0000000040918000      12 ----- 0000000040918000 000:00000   [ anon ]
000000004091b000    1016 rwx-- 000000004091b000 000:00000   [ anon ]
0000000041251000       4 ----- 0000000041251000 000:00000   [ anon ]
0000000041252000    1024 rwx-- 0000000041252000 000:00000   [ anon ]
0000000041c35000       4 ----- 0000000041c35000 000:00000   [ anon ]
0000000041c36000    1024 rwx-- 0000000041c36000 000:00000   [ anon ]
0000000041d36000      12 ----- 0000000041d36000 000:00000   [ anon ]
0000000041d39000    1016 rwx-- 0000000041d39000 000:00000   [ anon ]
0000000041e37000      12 ----- 0000000041e37000 000:00000   [ anon ]
0000000041e3a000    1016 rwx-- 0000000041e3a000 000:00000   [ anon ]
0000000041f38000      12 ----- 0000000041f38000 000:00000   [ anon ]
0000000041f3b000    1016 rwx-- 0000000041f3b000 000:00000   [ anon ]
0000000042039000      12 rwx-- 0000000042039000 000:00000   [ anon ]
000000004203c000    1016 rwx-- 000000004203c000 000:00000   [ anon ]
000000004213a000      12 rwx-- 000000004213a000 000:00000   [ anon ]
000000004213d000    1016 rwx-- 000000004213d000 000:00000   [ anon ]
0000000045553000   26104 rwx-- 0000000045553000 000:00000   [ anon ]
0000003384000000     104 r-x-- 0000000000000000 0fd:00000 ld-2.5.so
000000338421a000       4 r-x-- 000000000001a000 0fd:00000 ld-2.5.so
000000338421b000       4 rwx-- 000000000001b000 0fd:00000 ld-2.5.so
0000003384400000    1320 r-x-- 0000000000000000 0fd:00000 libc-2.5.so
000000338454a000    2044 ----- 000000000014a000 0fd:00000 libc-2.5.so
0000003384749000      16 r-x-- 0000000000149000 0fd:00000 libc-2.5.so
000000338474d000       4 rwx-- 000000000014d000 0fd:00000 libc-2.5.so
000000338474e000      20 rwx-- 000000338474e000 000:00000   [ anon ]
0000003384800000     520 r-x-- 0000000000000000 0fd:00000 libm-2.5.so
0000003384882000    2044 ----- 0000000000082000 0fd:00000 libm-2.5.so
0000003384a81000       4 r-x-- 0000000000081000 0fd:00000 libm-2.5.so
0000003384a82000       4 rwx-- 0000000000082000 0fd:00000 libm-2.5.so
0000003384c00000       8 r-x-- 0000000000000000 0fd:00000 libdl-2.5.so
0000003384c02000    2048 ----- 0000000000002000 0fd:00000 libdl-2.5.so
0000003384e02000       4 r-x-- 0000000000002000 0fd:00000 libdl-2.5.so
0000003384e03000       4 rwx-- 0000000000003000 0fd:00000 libdl-2.5.so
0000003385000000      84 r-x-- 0000000000000000 0fd:00000 libpthread-2.5.so
0000003385015000    2044 ----- 0000000000015000 0fd:00000 libpthread-2.5.so
0000003385214000       4 r-x-- 0000000000014000 0fd:00000 libpthread-2.5.so
0000003385215000       4 rwx-- 0000000000015000 0fd:00000 libpthread-2.5.so
0000003385216000      16 rwx-- 0000003385216000 000:00000   [ anon ]
000000338b800000      84 r-x-- 0000000000000000 0fd:00000 libnsl-2.5.so
000000338b815000    2044 ----- 0000000000015000 0fd:00000 libnsl-2.5.so
000000338ba14000       4 r-x-- 0000000000014000 0fd:00000 libnsl-2.5.so
000000338ba15000       4 rwx-- 0000000000015000 0fd:00000 libnsl-2.5.so
000000338ba16000       8 rwx-- 000000338ba16000 000:00000   [ anon ]
000000338f600000      68 r-x-- 0000000000000000 0fd:00000 libresolv-2.5.so
000000338f611000    2048 ----- 0000000000011000 0fd:00000 libresolv-2.5.so
000000338f811000       4 r-x-- 0000000000011000 0fd:00000 libresolv-2.5.so
000000338f812000       4 rwx-- 0000000000012000 0fd:00000 libresolv-2.5.so
000000338f813000       8 rwx-- 000000338f813000 000:00000   [ anon ]
00002aaaaaaab000     792 r-xs- 0000000000000000 0fd:00000 localedata.jar
00002aaaaab71000     156 r-xs- 0000000000000000 0fd:00000 sunjce_provider.jar
00002aaaaab98000     172 r-xs- 0000000000000000 0fd:00000 sunpkcs11.jar
00002aaaaabc3000      12 r-xs- 0000000000000000 0fd:00000 dnsns.jar
00002aaaaabc6000       8 r-xs- 0000000000000000 0fd:00000 dbutils.jar
00002aaaaabc8000       4 r-xs- 0000000000000000 0fd:00000 enums.jar
00002aaaaabc9000      16 r-xs- 0000000000000000 0fd:00000 inccon.jar
00002aaaaabcd000       8 r-xs- 0000000000000000 0fd:00000 miscutils.jar
00002aaaaabcf000       4 r-xs- 0000000000000000 0fd:00000 exceptions.jar
00002aaaaabd0000       4 r-xs- 0000000000000000 0fd:00000 tcutils.jar
00002aaaaabd1000    1400 r-xs- 0000000000000000 0fd:00000 jdbc.jar
00002aaaaad2f000      84 r-xs- 0000000000000000 0fd:00000 geocoding.jar
00002aaaaad44000     352 r-xs- 0000000000000000 0fd:00000 log4j-1.2.12.jar
00002aaaaad9c000     436 r-xs- 0000000000000000 0fd:00000 mysql-connector-java-3.1.12-bin.jar
00002aaaaae09000      72 r-x-- 0000000000000000 0fd:00000 libnet.so
00002aaaaae1b000    1020 ----- 0000000000012000 0fd:00000 libnet.so
00002aaaaaf1a000      12 rwx-- 0000000000011000 0fd:00000 libnet.so
00002aaaaaf40000      16 r-x-- 0000000000000000 0fd:00000 libnss_dns-2.5.so
00002aaaaaf44000    2044 ----- 0000000000004000 0fd:00000 libnss_dns-2.5.so
00002aaaab143000       4 r-x-- 0000000000003000 0fd:00000 libnss_dns-2.5.so
00002aaaab144000       4 rwx-- 0000000000004000 0fd:00000 libnss_dns-2.5.so
00002aaaac000000   35632 rwx-- 00002aaaac000000 000:00000   [ anon ]
00002aaaae2cc000   29904 ----- 00002aaaae2cc000 000:00000   [ anon ]
00002aaab0000000     160 rwx-- 00002aaab0000000 000:00000   [ anon ]
00002aaab0028000   55092 r-x-- 0000000000000000 0fd:00000 locale-archive
00002afeed636000       4 rwx-- 00002afeed636000 000:00000   [ anon ]
00002afeed65a000      12 rwx-- 00002afeed65a000 000:00000   [ anon ]
00002afeed65d000    7004 r-x-- 0000000000000000 0fd:00000 libjvm.so
00002afeedd34000    1028 ----- 00000000006d7000 0fd:00000 libjvm.so
00002afeede35000    1516 rwx-- 00000000006d8000 0fd:00000 libjvm.so
00002afeedfb0000     192 rwx-- 00002afeedfb0000 000:00000   [ anon ]
00002afeedfe0000       4 r-x-- 00002afeedfe0000 000:00000   [ anon ]
00002afeedfe1000       4 rwx-- 00002afeedfe1000 000:00000   [ anon ]
00002afeedfe2000      28 r-x-- 0000000000000000 0fd:00000 libhpi.so
00002afeedfe9000    1028 ----- 0000000000007000 0fd:00000 libhpi.so
00002afeee0ea000      12 rwx-- 0000000000008000 0fd:00000 libhpi.so
00002afeee0ed000      32 rwxs- 0000000000000000 0fd:00000 12331
00002afeee110000      40 r-x-- 0000000000000000 0fd:00000 libnss_files-2.5.so
00002afeee11a000    2044 ----- 000000000000a000 0fd:00000 libnss_files-2.5.so
00002afeee319000       4 r-x-- 0000000000009000 0fd:00000 libnss_files-2.5.so
00002afeee31a000       4 rwx-- 000000000000a000 0fd:00000 libnss_files-2.5.so
00002afeee31b000      52 r-x-- 0000000000000000 0fd:00000 libverify.so
00002afeee328000    1020 ----- 000000000000d000 0fd:00000 libverify.so
00002afeee427000      12 rwx-- 000000000000c000 0fd:00000 libverify.so
00002afeee42a000     144 r-x-- 0000000000000000 0fd:00000 libjava.so
00002afeee44e000    1024 ----- 0000000000024000 0fd:00000 libjava.so
00002afeee54e000      24 rwx-- 0000000000024000 0fd:00000 libjava.so
00002afeee554000      56 r-x-- 0000000000000000 0fd:00000 libzip.so
00002afeee562000    1032 ----- 000000000000e000 0fd:00000 libzip.so
00002afeee664000      16 rwx-- 0000000000010000 0fd:00000 libzip.so
00002afeee668000   39064 r-xs- 0000000000000000 0fd:00000 rt.jar
00002afef0c8e000     420 rwx-- 00002afef0c8e000 000:00000   [ anon ]
00002afef0cf7000     532 r-xs- 0000000000000000 0fd:00000 jsse.jar
00002afef0d7c000      84 r-xs- 0000000000000000 0fd:00000 jce.jar
00002afef0d91000    8560 r-xs- 0000000000000000 0fd:00000 charsets.jar
00002afef15ed000    3584 rwx-- 00002afef15ed000 000:00000   [ anon ]
00002afef196d000   45568 rwx-- 00002afef196d000 000:00000   [ anon ]
00002afef45ed000      56 rwx-- 00002afef45ed000 000:00000   [ anon ]
00002afef45fb000     712 rwx-- 00002afef45fb000 000:00000   [ anon ]
00002afef46b0000   21248 rwx-- 00002afef46b0000 000:00000   [ anon ]
00002afef5b70000   64768 rwx-- 00002afef5b70000 000:00000   [ anon ]
00002afef9ab0000    3520 rwx-- 00002afef9ab0000 000:00000   [ anon ]
00002afef9e20000    2668 rwx-- 00002afef9e20000 000:00000   [ anon ]
00002afefa0bb000     124 rwx-- 00002afefa0bb000 000:00000   [ anon ]
00002afefa0da000      24 rwx-- 00002afefa0da000 000:00000   [ anon ]
00002afefa0e0000      44 rwx-- 00002afefa0e0000 000:00000   [ anon ]
00002afefa0eb000     124 rwx-- 00002afefa0eb000 000:00000   [ anon ]
00007fffbd274000      12 ----- 00007fffbd274000 000:00000   [ anon ]
00007fffbd277000    2036 rwx-- 00007fffbd277000 000:00000   [ stack ]
ffffffffff600000    8192 ----- 0000000000000000 000:00000   [ anon ]
mapped: 402284K    writeable/private: 225024K    shared: 51720K

[Venkat Sadasivam]

A few years back I tried with YourKit profiler it has neat GUI to present data.

[Susan Smith]

Venkat,

Thanks for your reply. I actually already use VisualVM from Java to monitor this.

Another example, I run another Java program with -mx2m option but the writeable/ private almost 140M (based on the link that I sent to you I need to look at the writeable/ private)...

So I'm confused ... it's Java actually use more memory thatn what's in heap and stack?

Should I transfer this question to Linux forum probably?

[Susan Smith]

Even the smallest program like this:

public class test
{
        public static void main(String[] args)
        {
try{
                while ( true )
                {
 
                        System.out.println("Time now is: " + new java.util.Date());
                        Thread.sleep(2 * 60 * 1000);
                }
 
}catch (Exception ex)
{
        ex.printStackTrace();
}
        }
}

has huge "writeable/private" number --> more than 100MB.