JDK-8081629 : CMS split_block() does not correctly fix up block-offset-table for large blocks
  • Type: Bug
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2015-06-01
  • Updated: 2016-04-19
  • Resolved: 2015-09-12
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JDK 9
9 b84Fixed
Related Reports
Duplicate :  
JDK-8079274 - Long ParNew Pauses When Large Static Object Previously Allocated
Relates :  
JDK-6977974 - CMS: blockOffsetTable.hpp:187 assert(!reducing || _offset_array[i] >= offset) failed: Not reducing
Description
When a large block is split in order to allocate a chunk at the beginning of the block, split_block() should fix the block-offset-table (BOT)  for the remainder of the free chunk but does not do so correctly when the remainder is large enough to use the logarithmic strides used for the BOT.  split_block() fixes the start of the remainder block but may damage that fix when the fixes for the logarithmic strides is attempted.
Comments
Jon's comment above should say JDK-8079274.
15-03-2016
Using the flag VerifyBlockOffsetArray in a debug build will verify this fix but any test run with it will run too long to be used as a regression test. The reproducer in 8069274 passes with VerifyBlockOffsetArray.
22-06-2015
ILW = Low (un-optimal block sizes selected), High (fairly often), High (none) = P4
03-06-2015