Increase memory limits for IcedTea

[Andrew Haley]

The fairly low default limits on PermGen and MaxHeap space cause a
great deal of trouble on Linux, partiularly when running Eclipse.
Fedora maintainers considered adding a special wrapper script to
Eclipse that sets "-XX:MaxPermSize=128m" or something similar, but
this would only solve the problem for Eclipse: non-Eclipse
applications would continue to be bitten the same way.

In the end, Sun's Java seems to be the only VM that is affected by the
VMGen limit, and there are many references on the web to confused
users hitting it and having no idea how to proceed.  It makes sense
for Fedora and other Linux distros to bump the limit to something that
better fits the kinds of applications people are running.

There was some talk about removing these limits entirely, but:

1.  It is sometimes useful to set a low limit for some processes in
order to prevent them going insane and monopolizing a machine.  This
is particularly useful if a server is the subject of a denial of
service attack.

2.  The Java VM needs hit its own memory limit before the operating
decides to kills it, so that a proper log and stack trace can be
produced.

3.  There may be other untoward consequences of removing these limits:
we don't think that the Java VM has ever been tested under such
conditions.  It would take a very careful code audit to show that
simply removing the checks doesn't violate assumptions in the VM.

Andrew.


2007-10-08  Andrew Haley  <aph at redhat.com>

	* patches/icedtea-memory-limits.patch: New file.
	Set maximum PermGen space to 128M, MaxHeap to 512M.
	* Makefile.am (ICEDTEA_PATCHES): Add icedtea-memory-limits.patch.

--- openjdk/hotspot/src/share/vm/runtime/globals.hpp~	2007-09-27 08:46:16.000000000 +0100
+++ openjdk/hotspot/src/share/vm/runtime/globals.hpp	2007-10-05 19:06:32.000000000 +0100
@@ -2612,7 +2612,7 @@
           "an OS lock")                                                     \
                                                                             \
   /* gc parameters */                                                       \
-  product(uintx, MaxHeapSize, ScaleForWordSize(64*M),                       \
+  product(uintx, MaxHeapSize, ScaleForWordSize(512*M),                       \
           "Default maximum size for object heap (in bytes)")                \
                                                                             \
   product_pd(uintx, NewSize, 						    \
--- openjdk/hotspot/src/cpu/x86/vm/c2_globals_x86.hpp~	2007-09-27 08:45:59.000000000 +0100
+++ openjdk/hotspot/src/cpu/x86/vm/c2_globals_x86.hpp	2007-10-05 19:02:37.000000000 +0100
@@ -101,7 +101,7 @@
 
 // Heap related flags
 define_pd_global(uintx, PermSize,    ScaleForWordSize(16*M));
-define_pd_global(uintx, MaxPermSize, ScaleForWordSize(64*M));
+define_pd_global(uintx, MaxPermSize, ScaleForWordSize(128*M));
 
 // Ergonomics related flags
 define_pd_global(bool, NeverActAsServerClassMachine, false);

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