Integrated: 8256415: Shenandoah: Should evacuate/update codecache concurrently when class unloading is off

[Zhengyu Gu]

On Tue, 17 Nov 2020 19:28:18 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> During isolating GC work (JDK-8255765), I found that Shenandoah still evacuate/update codecache roots at final mark safepoint when class unloading is off.
> 
> Actually, it can be done concurrently by utilizing nmethod_entry_barrier.
> 
> Shenandoah should always enable nmethod_entry_barrier for evacuation, regardless class unloading status, and perform code cache evacuation/updating during strong root processing.
> 
> Key points:
> 1) Always enable nmethod entry barrier
> 2) Always attach ShenandoahNMethod to nmethod, regardless weather class unloading is enabled
> 3) Only evacuate/update thread and serial weak roots at final mark pause.
> 4) Code roots are evacuated/updated concurrently during weak roots (when class unloading is on) or strong roots (when class unloading is off)
> 
> 
> - [x] hotspot_gc_shenandoah
> - [x] tier1 with ShenandoahGC and +/-ClassUnloading

This pull request has now been integrated.

Changeset: eab170c0
Author:    Zhengyu Gu <zgu at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/eab170c0
Stats:     170 lines in 10 files changed: 56 ins; 91 del; 23 mod

8256415: Shenandoah: Should evacuate/update codecache concurrently when class unloading is off

Reviewed-by: rkennke

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PR: https://git.openjdk.java.net/jdk/pull/1271