I'm calling a bunch of shell programs from a program running on the JVM. When I execute a program like imagemagick, does it use my system's RAM or does it use RAM allocated to the JVM ?
If you run (shell) executables, they will use their own memory space in system RAM.
If you instead load DLLs using for example JNI and execute that code, they will be loaded into Java's memory space.
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I have a java program running in centos Box.
My -Xmx and -Xms set to 4000 Mb.
The program works fine.
But when i do free -m , the used memory is showing as 506 MB. As per my understanding , XMS memory should be reserved for JVM.Why does free command not showing the java used memory ?
I have also done jstat -gccapacity $(pidof java) and there NGCMN and NGCMX updated and have the same value ?
Any support would be helpful.
I'm running my program as java -Xms41000m -Xmx42000m -jar
Even when -Xmx and -Xms set to the same value, the space reserved for Java Heap is not immediately allocated in RAM.
Operating System typically allocates physical memory lazily, only on the first access to a virtual page. So, while unused part of Java Heap is not touched, it won't really consume memory.
You may use -XX:+AlwaysPreTouch option to forcibly touch all heap pages on JVM start.
I am getting the error message such as stack overflow, heap memory error and similar messages after trying to use TestNG. And after installing TestNg the Eclipse feels heavy and became very slow to respond. and throwing this error message.
An error of such kind Stackoverflow and heap memory error occurs because of physical lack of resources such as lower Ram or slower processor. So the only solution to this was to allocate more memory to eclipse IDE. you can allocate more memory to eclipse by finding the eclipse.ini file in your directory where you have installed it. After finding the file, the file should be in notepad. open the file in notepad and edit the memory allocated. there are two things you need to change. Xms and XMX, which is minimum and max memory. I made mine from 256m to 512m for XMS and from 1024m to 2048M. But make sure you allocate only the memory which is spare. otherwise your PC might crash. Hope this helps.
With QEMU, I can use either use -initrd '${images_dir}/rootfs.cpio for the initrd, or pass the initramfs image directly to -kernel Image.
But if I try the initramfs image with gem5 fs.py --kernel Image it fails with:
fatal: Could not load kernel file
with the exact same initramfs kernel image that QEMU was able to consume.
And I don't see an analogue to -initrd.
The only method that I got to work was to pass an ext2 disk image to --disk-image with the raw vmlinux.
https://www.mail-archive.com/gem5-users#gem5.org/msg15198.html
initrd appears unimplemented on arm and x86 at least, since gem5 must know how to load it and inform the kernel about it's location, and grepping initrdonly shows some ARM hits under:
src/arch/arm/linux/atag.hh
but they are commented out.
Communicating the initrd to the kernel now appears to be simply doable via the DTB chosen node linux,initrd-start and linux,initrd-end properties, so it might be very easy to implement: https://www.kernel.org/doc/Documentation/devicetree/bindings/chosen.txt (and gem5's existing DTB auto generation) + reusing the infrastructure to load arbitrary bytes to a memory location: How to preload memory with given raw bytes in gem5 from the command line in addition to the main ELF executable?
Initramfs doesn't work because gem5 can only boot from vmlinux which is the raw ELF file, and the initramfs images only gets attached by the kernel build to a more final image type like Image or bzImage which QEMU can use to boot, see also: https://unix.stackexchange.com/questions/5518/what-is-the-difference-between-the-following-kernel-makefile-terms-vmlinux-vml/482978#482978
Edit: the following is not needed anymore after the patch mentioned at: How to attach multiple disk images in a simulation with gem5 fs.py? To do this test, I also had to pass a dummy disk image as of gem5 7fa4c946386e7207ad5859e8ade0bbfc14000d91 since the scripts don't handle a missing --disk-image well, you can just dump some random 512 bytes and use them:
dd if=/dev/zero of=dummy.iso bs=512 count=1
My test execution shows "gc memory overhead exceeded" exception in linux cent os 7. I changed jmeter.bat's heap max size 6g and min size as 512m. I am not used any listeners, preprocessor, http header manager. Used regular expression extractor for 2 samplers and constant timer as common. I run my test in terminal and store result in jtl file. I run it for 250 users, rampup period as 1 and scheduler as 5400 seconds. But still issue persist..
System configuration:
Ram 8 GB
CPU octa core 3.12 GHz
Swap memory 16 GB
You say that you changed jmeter.bat, but the problem is on Linux, which doesn't use jmeter.bat. Unless it's a typo, try to change jmeter or jmeter.sh (whichever one you use to invoke JMeter).
Generally I would not recommend more than 2GB for moderate use, and 4GB for heavy use. For instance my settings are:
HEAP="-Xms4096m -Xmx4096m"
and I can run up to 300 concurrent users with a lot of samplers/heavy scripting even in GUI mode. Setting larger heap may cause larger pauses on GC, which can cause the exception you are getting.
After you start JMeter, run the following command to make sure the memory settings are indeed as you expect them to be:
ps -ef | grep JMeter
I actually changed Xmx in jmeter.bat file instead of jmeter.sh file since i used linux for this test. Jmeter.bat is supported in windows os and jmeter.sh is supported for Linux os. So that the above mentioned error occurred. Once I changed it in jmeter.sh file it works perfectly.
As per my knowledge, JVM is a process virtual machine which means it does not emulate the entire existing computer architechture but emulates/mimics only the cpu of the host computer.
Now, my question is:
Why a .class java file needs to be executed inside virtual CPU(i.e. JVM) instead of being executed on actual CPU memory of the host computer?
For code to run on the actual CPU, it has to be in the instruction set of that CPU. Each CPU architecture has its own, distinct instruction set, so code written for one CPU won't run on another type of CPU.
The point of defining a Java Virtual Machine is so that the code will run on any type of computer, as long as it has a JVM interpreter.
The JVM instructions are not real CPU instructions but are for an abstract CPU.
Add to that some security proofs on the JVM byte code.
The JVM implementation's Just in Time compiler will translate abstract instructions to host CPU instructions on demand to achieve better performance.
JVM actually conversts the java bytecode to the instruction set applicable to that particular CPU.Every CPU do not have similar instruction set.
So .class file is generated as it can run on any CPU. JVM does the task of converting onto machin code applicable to it.