RFE (m): JDK-7197666: java -d64 -version core dumps in a box with lots of memory

[Bengt Rutisson]

Hi all,

Coleen and Thomas have already looked at the preliminary version of this 
request. Thanks!

Removing the preliminary part of this request now and asking for full 
reviews.

Here is an updated webrev based on the comments from Coleen and Thomas:

http://cr.openjdk.java.net/~brutisso/7197666/webrev.01/

Thanks,
Bengt


On 3/28/13 11:09 PM, Bengt Rutisson wrote:
>
> Hi all,
>
> Sending this to both runtime and GC since I think it concerns both areas.
>
> I'd like some feedback on this preliminary change. I still want to do 
> some more testing and evaluation before I ask for final reviews:
>
> http://cr.openjdk.java.net/~brutisso/7197666/webrev.00/
>
> In particular I would like some feedback on these questions:
>
> - I am adding a flag that has the same value on all platforms except 
> Solaris x86. There is the product_pd flag macro to support this. But 
> there is no experimental_pd marcro. I would have preferred to make my 
> new flag experimental. Should I add experimental_pd or should I just 
> use a product flag?
>
> - Even with product_pd I think I still have to go in to all the 
> different platform files and add the exact same code to give the flag 
> a default value on all platforms. Is there a way to have a default 
> value and only override it on Solaris x86?
>
> - The class I am adding, ArrayAllocator, wants to choose between doing 
> malloc and mmap. Normally we use ReservedSpace and VirtualSpace to get 
> mapped memory. However, those classes are kind of clumsy when I just 
> want to allocate one chunk of memory. It is much simpler to use the 
> os::reserve_memory() and os::commit_memory() methods directly. I think 
> my use case here motivate using these methods directly, but is there 
> some reason not to do that?
>
> Some background on the change:
>
> The default implementation of malloc on Solaris has several limitation 
> compared to malloc on other platforms. One limitation is that it can 
> only use one consecutive chunk of memory. Another limitation is that 
> it always allocates in this single chunk of memory no matter how large 
> the requested amount of memory is. Other malloc implementations 
> normally use mapped memory for large allocations.
>
> The Java heap is mapped in memory and we try to pick a good address 
> for it. The lowest allowed address is controlled by 
> HeapBaseMinAddress. This is only 256 MB on Solaris x86 (other 
> platforms have at least 2 GB). Since the C heap ends up below the Java 
> heap it means that in some cases it is limited to 256 MB.
>
> When we run with ParallelOldGC we get three task queues per GC thread. 
> Each task queue takes mallocs 1MB. The failing machine in the bug 
> report has lots of CPUs and ends up with 83 GC threads. This is 249 
> MB, which is more than we can get out of the 256 MB limited C heap 
> considering that there are other things that get malloced too.
>
> So, the problems occur mostly on Solaris x86. My suggested fix tries 
> to address this by letting the task queues be mapped instead of 
> malloced on Solaris x86. Instead of inlining this logic in 
> taskqueue.cpp I added a more general class. The reason for this is 
> that I think we need to use the same logic in more places, especially 
> for G1, which is mallocing quite a lot.
>
> Since I think malloc on other platforms use mapped memory for large 
> malloc requests I think it is enough for this change to have effect on 
> Solaris. The other platforms probably have better heuristics than I 
> can come up with for which sizes should be mapped. On Sparc we have 
> the same limitation with malloc, but we have more memory available for 
> the C heap. This is why I have only enabled this for Solaris x86.
>
> Also, I will be on vacation for a few days. Back in the office 
> Thrusday April 4. I'm happy for any feedback on this, but if I don't 
> respond until next week you know why :)
>
> Thanks,
> Bengt

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