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

[Coleen Phillimore]

On 04/04/2013 07:32 AM, Bengt Rutisson wrote:
>
>
> Hi Colleen,
>
> Thank you so much for looking at this!
>
> On 4/1/13 11:04 PM, Coleen Phillimore wrote:
>>
>> Bengt,
>>
>> This is a nice way to solve this, although don't know why you don't 
>> just use mmap for all the task queues.   You don't allocate and 
>> deallocate them a lot, do you?
>
> Right, I was thinking about using mmap directly but when I looked at 
> the current usages of ::mmap I can only find that it is being used in 
> src/os files. So, it seems to me like this is not the API we are 
> supposed to use in the rest of the code. The next level of abstraction 
> is os::reserve_memory() and os::commit_memory(), so that's why I 
> picked them. It would have been nice if I could have just used 
> os::commit_memory(), but internally it uses MAP_FIXED which means that 
> I can't pass NULL as the addr parameter. So, I have to use 
> os::reserve_memory() first.
>
> Are you ok with these calls, or do you think I should change to use 
> mmap directly?

Oh, no, I think you should use os::reserve_memory().   My question was 
why do you conditionally use reserve_memory vs. os::malloc() for these 
task queues.  Or are they always big enough that they'll end up using 
os::reserve_memory().
>
>>
>> You can also use the trick in globals.hpp:
>>
>> *+   product(uintx, ArrayAllocatorMallocLimit, SOLARIS_ONLY(64K) NOT_SOLARIS(MAX_UINT),  \*
>> *+           "Allocation less than this value will be allocated "              \*
>> *+           "using malloc. Larger allocations will use mmap.")*
>>
>> And include both solaris sparc and x86 in the size calculation (since 
>> sparc malloc has the same problem as x86 just not as bad), and save 
>> editing all the globals_<os_cpu>.hpp files.
>
> Thanks! This is much better! It also means that I can use an 
> experimental flag, so I'll change to that.

Yes, I guess it's better as an experimental flag.  It could be product 
also.  People might want their own sizes.

Coleen

>
>
> Thanks again for this feedback. It was exactly what I needed. I'll 
> send out an updated webrev and a "real" review request soon.
>
> Bengt
>
>>
>> Coleen
>>
>> On 03/28/2013 06:09 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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