Code review request: JDK-8001592 NMT: assertion failed: assert(_amount >= amt) failed: Just check: memBaseline.hpp:180

Karen Kinnear karen.kinnear at
Thu Nov 8 08:19:47 PST 2012


Code looks good. Thank you for the fixes.

Minor comments:
1. memBaseline.cpp line 119 anonymouse -> anonymous

2. Much prefer the new MallocRecordIterator::current() behavior!!!

3. MallocRecordIterator::next()
Can you possibly clarify? Lines 194-195 say that if there is an associated
arena record it has to be the previous because of sorting order?
 -- what about sorting order means it is previous?
 - and it appears that you are looking at next_rec relative to prev_rec. What about 
   the current rec - isn't that in the middle?

- and many thanks for the detailed code comments and improved variable names.


On Nov 7, 2012, at 11:26 AM, Zhengyu Gu wrote:

> The assertion failure reflects that total memory that backs arenas are greater than total memory chunks for backing all arenas, which is obviously incorrect.
> The problem is due to Arena object, although it is declared as C-heap object, but it is used as value objects and stack objects as well. Value and stack objects do not have tracking records in NMT, which can leave arena size records alone in NMT. Because NMT uses Arena's deallocation records to cleanup size records, that means those leftover size records are not get cleanup.
> The solution is to use Arena's destructor to reset arena size to 0, and NMT uses this record to remove the corresponding record.
> The webrev also cleanup Memsnapshot::merge() routine, since virtual memory records now are stored in separate array, malloc staging area can keep only one record for each address (whoever has higher sequence number win), which should reduce memory usage by NMT.
> Webrev:
> Tests:
>  vm.quick.testlist on Linux 32, Windows x64, Solaris AMD64 and Sparcv9
>  JPTR tests
> Thanks,
> -Zhengyu

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