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  1. JDK
  2. JDK-8170817

G1: Returning MinTLABSize from unsafe_max_tlab_alloc causes TLAB flapping

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    • gc
    • b20

    Description

      G1 seems to be susceptible to the same problem Shenandoah faced, see the description here:
       http://mail.openjdk.java.net/pipermail/shenandoah-dev/2016-December/001275.html

      In short, returning MinTLABSize from unsafe_max_tlab_alloc when there is no space in the region makes the allocation mechanics to allocate MinTLABSize-sized TLAB in the next free region, fragmenting it. Shenandoah fixed this by returning the size of the next region, which we know is free (http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/7009fc6f74b3), not sure the same can be done for G1.

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              iwalulya Ivan Walulya
              shade Aleksey Shipilev
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