RFR (S) 8213373: Bulk MarkBitMap clearing methods

Aleksey Shipilev shade at redhat.com
Mon Nov 12 16:12:53 UTC 2018


On 11/05/2018 06:17 PM, Aleksey Shipilev wrote:
> RFE:
>   https://bugs.openjdk.java.net/browse/JDK-8213373
> 
> Fix:
>   http://cr.openjdk.java.net/~shade/8213373/webrev.00/
> 
> We have found this a while ago in Shenandoah: there is an easy improvement for older compilers,
> non-optimized builds, unusual build modes. This micro-optimization is sometimes very fruitful, and
> it makes us less reliant on smart compilers. It depends on JDK-8211926 fixed first.

JDK-8211926 is in.

> The impact of this is difficult to measure with G1, but here are historical figures from Shenandoah
> here: http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-January/001564.html
> 
> I put the _large calls in G1 where it seems to fit: where we clear the bitmaps in bulk, e.g. from
> bottom to end of the heap region. Shenandoah does it on all paths, including from bottom to top,
> without apparent loss.
> 
> Testing: hotspot tier1

This passed jdk-submit as well.

Thanks,
-Aleksey

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