RFR: 8315247: GenShen: Condition calls to post-write barrier code generation by a flag

[Kelvin Nilsen]

On Mon, 28 Aug 2023 21:28:21 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp line 523:
>> 
>>> 521:   product(bool, ShenandoahCardBarrier, false, DIAGNOSTIC,                   \
>>> 522:           "Turn on/off card-marking post-write barrier in Shenandoah")      \
>>> 523:                                                                             \
>> 
>> I was thinking this would not be visible on the command line.  If we make it visible, then we would need to assure consistency with mode == generational.
>> 
>> My thought was we would just set this global variable in, for example, ShenandoahArguments::initialize() if !strcmp(ShenandoahGCMode, "generational")
>
> This approach has parity with the other barrier flags. `shenandoahGenerationalMode.cpp` asserts that the flag is on. 
> 
> It shouldn't be strictly necessary with the default being `false`, but we may want to have `shenandoahPassiveMode.cpp` explicitly turn this flag off as it does the other barrier flags.

If we make this visible on the command line, we will want to make sure it is consistent with mode->is_generational().  Right?

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/313#discussion_r1307995770