JDK-8030177 : G1: Enable TLAB resizing
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: gc
  • Affected Version: hs24,hs25
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2013-12-16
  • Updated: 2016-03-01
  • Resolved: 2014-01-27
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JDK 8 JDK 9
8u20Fixed 9 b03Fixed
Related Reports
Duplicate :  
JDK-8028312 - Investigate g1 TLAB size
Duplicate :  
JDK-7189528 - Use containing heap or generation to bound PLAB sizes suggested by PLABStats instances
Description
Currently G1 does not resize TLABs. This reduces performance for G1 since it can lead to contention in the allocation path.

Performance test show 2-3% throughput improvement when resizing TLABs up to the humongous threshold.
Comments
noreg-hard motivation: I have a small Java program that has two threads. One allocates a lot and one allocates very little. I did JFR recordings and looked at the object_alloc_in_new_TLAB event to see the TLAB sizes. The fast allocator gets large TLABs and the slow allocator gets small TLABs after my change. I tried turning this in to a JTreg test. If I use JFR events to do verification I need access to the JFR parser. That means I have to put the test in among the JFR tests in the JDK. That seems like the wrong place to put a test for a Hotspot feature. I tried using the PrintTLAB flag instead and parse the output. But that output does not contain the thread names, so I can't determine which threads that are the fast and slow allocators.
29-01-2014