Heap size limit

[Panagiotis Astithas]

Greg Lewis wrote:
> On Fri, Apr 23, 2004 at 09:49:27AM -0400, Paul Dlug wrote:
> 
>>I'm trying to start a JVM with a large heap size and getting an error 
>>message:
>>
>>java -Xms256m -Xmx2024m
>>Error occurred during initialization of VM
>>Could not reserve enough space for object heap
>>
>>I tried a bunch of different sizes and anything under 2024m works just 
>>fine so this appears to be a hard limit. I've tried changing a few 
>>system parameters but can't seem to stumble on the right one. Can 
>>someone help me out with this?
> 
> 
> Obviously I'm a long way behind on freebsd-java, but I'm catching up now...
> 
> My strong suggestion is that you're hitting the maximum amount of memory
> that your user can mmap.  I'm not exactly sure what setting dictate that,
> but its almost certainly what you're running into.

Definitely:
ktrace java -Xms256m -Xmx2024m

[...]
  15034 java     CALL  mmap(0,0x82800000,0,0x1042,0xffffffff,0,0,0)
  15034 java     RET   mmap -1 errno 22 Invalid argument
  15034 java     CALL  write(0x1,0xbfbfd670,0x2b)
  15034 java     GIO   fd 1 wrote 43 bytes
        "Error occurred during initialization of VM
        "
  15034 java     RET   write 43/0x2b
  15034 java     CALL  write(0x1,0xbfbfd670,0x2e)
  15034 java     GIO   fd 1 wrote 46 bytes
        "Could not reserve enough space for object heap"
[...]


% grep 22 /usr/include/errno.h
#define EINVAL          22              /* Invalid argument */

%man mmap
[...]

      [EINVAL]    MAP_FIXED was specified and the addr argument was not
                  page aligned, or part of the desired address space
                  resides out of the valid address space for a user
                  process.
[...]


Now try changing vm.max_proc_mmap to an insanely large value:

# sysctl vm.max_proc_mmap=10000000000000
vm.max_proc_mmap: 26960 -> 2147483647

We see the requested size gets truncated to 2 GB.
This still doesn't help us, though:

# /usr/local/jdk1.4.2/bin/java -Xms256m -Xmx2024m
Error occurred during initialization of VM
Could not reserve enough space for object heap


The weird thing is that in a GENERIC kernel, the kernel/userland address 
space split is 1 GB / 3 GB. As it can bee sen from the following excerpt 
from /sys/i386/conf/NOTES:

#
# Change the size of the kernel virtual address space.  Due to
# constraints in loader(8) on i386, this must be a multiple of 4.
# 256 = 1 GB of kernel address space.  Increasing this also causes
# a reduction of the address space in user processes.  512 splits
# the 4GB cpu address space in half (2GB user, 2GB kernel).
#
options         KVA_PAGES=260


Why you can't mmap up to 3 GB of memory, I don't know. Perhaps we should 
take it to -current or -hackers.

Cheers,
-- 
Panagiotis Astithas
Electrical & Computer Engineer, PhD
Network Management Center
National Technical University of Athens, Greece