Java maximum memory on Windows XP

Question

I've always been able to allocate 1400 megabytes for Java SE running on 32-bit Windows XP (Java 1.4, 1.5 and 1.6).

java -Xmx1400m ...

Today I tried the same option on a new Windows XP machine using Java 1.5_16 and 1.6.0_07 and got the error:

Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

Through trial and error it seems 1200 megabytes is the most I can allocate on this machine.

Any ideas why one machine would allow 1400 and another only 1200?

Edit: The machine has 4GB of RAM with about 3.5GB that Windows can recognize.

Crystie

You would notice a difference in the maximum between running the app in a 32-bit shell or a 64-bit shell, at least in my experience, although 64-bit WindowsXP systems are rare. – Crossman

wiki.eclipse.org/Eclipse.ini - oracle.com/technetwork/java/javase/… – Lignocellulose

Answer 1

Keep in mind that Windows has virtual memory management and the JVM only needs memory that is contiguous in its address space. So, other programs running on the system shouldn't necessarily impact your heap size. What will get in your way are DLL's that get loaded in to your address space. Unfortunately optimizations in Windows that minimize the relocation of DLL's during linking make it more likely you'll have a fragmented address space. Things that are likely to cut in to your address space aside from the usual stuff include security software, CBT software, spyware and other forms of malware. Likely causes of the variances are different security patches, C runtime versions, etc. Device drivers and other kernel bits have their own address space (the other 2GB of the 4GB 32-bit space).

You could try going through your DLL bindings in your JVM process and look at trying to rebase your DLL's in to a more compact address space. Not fun, but if you are desperate...

Alternatively, you can just switch to 64-bit Windows and a 64-bit JVM. Despite what others have suggested, while it will chew up more RAM, you will have much more contiguous virtual address space, and allocating 2GB contiguously would be trivial.

Aureomycin

Use Process Explorer to see where in memory dll's are being loaded. Often some updated driver will stick itself in the middle of your address space. Using the REBASE command you can easily push these out of the way. Keep in mind though, the dll is subject to get updated again and break things. – Bittencourt

@Christopher, Is it possible to use 64-bit JVM on a 32-bit Windows XP? – Squarerigger

@Squarerigger Sorry, I missed your query. AFAIK, it is not possible. OS X had some tricks for 64-bit user space with 32-bit kernels, but I've not heard of any such thing for Windows. – Aureomycin

@ChristopherSmith, Btw, you mentioned "other programs running on the system shouldn't necessarily impact your heap size". If so, how do we explain this result: #9304389 ? – Squarerigger

@Bittencourt How do you use process explorer to see the loaded dlls? – Fullblooded

can similar problem occur due to the use of shared libraries on a Unix system? – Thumbscrew

Answer 2

This has to do with contiguous memory.

Here's some info I found online for somebody asking that before, supposedly from a "VM god":

The reason we need a contiguous memory region for the heap is that we have a bunch of side data structures that are indexed by (scaled) offsets from the start of the heap. For example, we track object reference updates with a "card mark array" that has one byte for each 512 bytes of heap. When we store a reference in the heap we have to mark the corresponding byte in the card mark array. We right shift the destination address of the store and use that to index the card mark array. Fun addressing arithmetic games you can't do in Java that you get to (have to :-) play in C++.

Usually we don't have trouble getting modest contiguous regions (up to about 1.5GB on Windohs, up to about 3.8GB on Solaris. YMMV.). On Windohs, the problem is mostly that there are some libraries that get loaded before the JVM starts up that break up the address space. Using the /3GB switch won't rebase those libraries, so they are still a problem for us.

We know how to make chunked heaps, but there would be some overhead to using them. We have more requests for faster storage management than we do for larger heaps in the 32-bit JVM. If you really want large heaps, switch to the 64-bit JVM. We still need contiguous memory, but it's much easier to get in a 64-bit address space.

Creekmore

That is very interesting. I always asked myself why 1500 MB, now I got it, thanks! – Sirkin

Sorry for following up on an ages old question, but this is the best answer i have seen so far. But why does the JVM fail at startup if it cannot get the maximum heap size? Shouldn't it quietly settle for the best size above minimum? – Medievalist

Answer 3

The Java heap size limits for Windows are:

• maximum possible heap size on 32-bit Java: 1.8 GB
• recommended heap size limit on 32-bit Java: 1.5 GB (or 1.8 GB with /3GB option)

This doesn't help you getting a bigger Java heap, but now you know you can't go beyond these values.

Achlamydeous

Answer 4

Oracle JRockit, which can handle a non-contiguous heap, can have a Java heap size of 2.85 GB on Windows 2003/XP with the /3GB switch. It seems that fragmentation can have quite an impact on how large a Java heap can be.

Sciomancy

Answer 5

The JVM needs contiguous memory and depending on what else is running, what was running before, and how windows has managed memory you may be able to get up to 1.4GB of contiguous memory. I think 64bit Windows will allow larger heaps.

Shirline

I think modern operating system emulate continuous memory for the. Since the 80486 the x86-architecture supports paging to make it easy to rearrange the physical memory. – Calmas

Mnemeth: First, there is a specific API (AllocateUserPhysicalPages) in WINAPI for advanced tools like databases and VMs that are better off with managing their memory themselves with Windows out of the way. Second, paging is a 80386 protected mode feature, not 80486. – Ayeaye

Answer 6

Sun's JVM needs contiguous memory. So the maximal amount of available memory is dictated by memory fragmentation. Especially driver's dlls tend to fragment the memory, when loading into some predefined base address. So your hardware and its drivers determine how much memory you can get.

Two sources for this with statements from Sun engineers: forum blog

Maybe another JVM? Have you tried Harmony? I think they planned to allow non-continuous memory.

Anatomist

But I was able to allocate 1300MB on a machine with only 1GB of RAM (plus virtual memory). My 2GB RAM machine (also with virtual memory) can only allocate 1200MB. – Crystie

Harmony is dead isn't it? – Squarerigger

Yep: "Apache Harmony is retired at the Apache Software Foundation since Nov 16, 2011." – Manumission

Answer 7

I think it has more to do with how Windows is configured as hinted by this response: Java -Xmx Option

Some more testing: I was able to allocate 1300MB on an old Windows XP machine with only 768MB physical RAM (plus virtual memory). On my 2GB RAM machine I can only get 1220MB. On various other corporate machines (with older Windows XP) I was able to get 1400MB. The machine with a 1220MB limit is pretty new (just purchased from Dell), so maybe it has newer (and more bloated) Windows and DLLs (it's running Window XP Pro Version 2002 SP2).

Crystie

It could affected by your Virtual Memory settings also. – Blowfish

All the machines I test with have virtual memory at least twice that of the physical RAM. – Crystie

note that you really never want to really use virtual memory with java,because GC performance will become very bad The amount of memory depends on which dll's have already been loaded and have fragmented the memory. – Avrilavrit

Answer 8

I got this error message when running a java program from a (limited memory) virtuozzo VPS. I had not specified any memory arguments, and found I had to explicitly set a small amount as the default must have been too high. E.g. -Xmx32m (obviously needs to be tuned depending on the program you run).

Just putting this here in case anyone else gets the above error message without specifying a large amount of memory like the questioner did.

Indicate

Answer 9

sun's JDK/JRE needs a contiguous amount of memory if you allocate a huge block.

The OS and initial apps tend to allocate bits and pieces during loading which fragments the available RAM. If a contiguous block is NOT available, the SUN JDK cannot use it. JRockit from Bea(acquired by Oracle) can allocate memory from pieces.

Single

Answer 10

Everyone seems to be answering about contiguous memory, but have neglected to acknowledge a more pressing issue.

Even with 100% contiguous memory allocation, you can't have a 2 GiB heap size on a 32-bit Windows OS (*by default). This is because 32-bit Windows processes cannot address more than 2 GiB of space.

The Java process will contain perm gen (pre Java 8), stack size per thread, JVM / library overhead (which pretty much increases with each build) all in addition to the heap.

Furthermore, JVM flags and their default values change between versions. Just run the following and you'll get some idea:

 java -XX:+PrintFlagsFinal

Lots of the options affect memory division in and out of the heap. Leaving you with more or less of that 2 GiB to play with...

To reuse portions of this answer of mine (about Tomcat, but applies to any Java process):

The Windows OS limits the memory allocation of a 32-bit process to 2 GiB in total (by default).

[You will only be able] to allocate around 1.5 GiB heap space because there is also other memory allocated to the process (the JVM / library overhead, perm gen space etc.).

Why does 32-bit Windows impose a 2 GB process address space limit, but 64-bit Windows impose a 4GB limit?

Other modern operating systems [cough Linux] allow 32-bit processes to use all (or most) of the 4 GiB addressable space.

That said, 64-bit Windows OS's can be configured to increase the limit of 32-bit processes to 4 GiB (3 GiB on 32-bit):

http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx

Bistre

This answer only addresses why he might only be able to allocate 2 GB, not why he can allocate 1.4 GB on one computer and only 1.2 GB on another. He doesn't hit either your 1.5 GB, 2 GB, or 4 GB limits stated here. – Arie

The paragraph on JVM flags goes some way to explain why memory might vary between versions. Also, note my point around how the heap setting is always a (large) fraction of the total process size - so a setting below that may still hit the 2 GiB process limit - another might be constrained by contiguous memory allocation. – Bistre

Or possibly the 1.5 GB limit, on that 1.4 GB allocation he is doing. Makes more sense now - thanks for that clarification. – Arie

Answer 11

Here is how to increase the Paging size

1. right click on mycomputer--->properties--->Advanced
2. in the performance section click settings
3. click Advanced tab
4. in Virtual memory section, click change. It will show ur current paging size.
5. Select Drive where HDD space is available.
6. Provide initial size and max size ...e.g. initial size 0 MB and max size 4000 MB. (As much as you will require)

Unwitting

Answer 12

**There are numerous ways to change heap size like,

1. file->setting->build, exceution, deployment->compiler here you will find heap size
2. file->setting->build, exceution, deployment->compiler->andriod here also you will find heap size. You can refer this for andriod project if you facing same issue.

What worked for me was

1. Set proper appropriate JAVA_HOME path incase you java got updated.

2. create new system variable computer->properties->advanced setting->create new system variable

name: _JAVA_OPTION value: -Xmx750m

FYI: you can find default VMoption in Intellij help->edit custom VM option , In this file you see min and max size of heap.**

Polonium

Answer 13

First, using a page-file when you have 4 GB of RAM is useless. Windows can't access more than 4GB (actually, less because of memory holes) so the page file is not used.

Second, the address space is split in 2, half for kernel, half for user mode. If you need more RAM for your applications use the /3GB option in boot.ini (make sure java.exe is marked as "large address aware" (google for more info).

Third, I think you can't allocate the full 2 GB of address space because java wastes some memory internally (for threads, JIT compiler, VM initialization, etc). Use the /3GB switch for more.

Inheritrix

The idea of a page file being useless with 4GB or RAM is wrong. Without a pagefile, the operating system cannot evict unused process data (stack space for unused services, etc) from physical RAM, thus lowering the amount of RAM available for real work. Having a pagefile frees up RAM. – Scopoline