JDK-6711930 : NUMA allocator: ParOld can create a hole less than minimal object size in the lgrp chunk
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs13
  • Priority: P3
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2008-06-07
  • Updated: 2011-03-08
  • Resolved: 2011-03-08
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JDK 6 JDK 7 Other
6u14Fixed 7Fixed hs13Fixed
Setting top in MutableNUMASpace can create a hole in chunk, which is less than a minimal object size in the lgrp chunk. The VM would typically fail while trying to fill the hole with a dummy object.

Internal Error at sharedHeap.cpp:279, pid=8687, tid=5
Error: assert(word_size == (size_t)oopDesc::header_size(),"Unaligned?")
Also, if a object crosses the chunk boundary a verification would fail, because it verifies each chunk independently. The failure will look like:
Internal Error at mutableSpace.cpp:130, pid=7099, tid=5
Error: guarantee(p == top(),"end of last object must match end of space")
There is also a fault in the allocation code, that enable creation of less than a minimal object sized holes between the lgrp chunks, which I had introduced while fixing 6697534.
Specifically in MutableNUMASpace::cas_allocate(), the code that computes the size of the hole created should be 

size_t remainder = pointer_delta(s->end(), p + size);

instead of

size_t remainder = pointer_delta(s->end(), p);

EVALUATION See description.