OpenJDK not ready for virtualized environments

[Andrew Haley]

On 07/13/2010 04:07 PM, Jaroslav Tulach wrote:
> Thanks for your comment Florian.
> 
> Dne úterý 06 
ervence 2010 15:55:32 Florian Weimer napsal(a):
>> * Jaroslav Tulach:
>>> After a discussion at #openjdk it looks like like a result of changing
>>> the defaults in amount of heap size and perm gen size. I believe the
>>> change is wrong. It shall rather check the # of available memory and if
>>> lower than 1GB stick with old defaults.
>>
>> Actually, the correct fix would be to reserve the address space
>> initially (so that you get one contiguous chunk), and allocate backing
>> store only as needed.
> 
> That would definitely be an improvement.

That's what it does already.

> On the other hand, do you think it makes sense to allocate more than
> is physically available? I have just 384MB or physical
> RAM. Requesting 640MB of virtual space looks too greedy to me.

>> On Linux, you can do this by specifying PROT_NONE to mmap() and use
>> mprotect() later. (MAP_NORESERVE is different, and difficult to get
>> right because the garbage collector must be prepared to deal with
>> SIGSEGV when the used portion of the heap expands during GC.)
> 
> This would be a change in upstream openjdk code, right?

No, that's what it does already.  We need to know why it's not working
for you.  See my message of July 6.

Andrew.