RFR: 8230109: G1DirtyCardQueueSet should use card counts rather than buffer counts
stefan.johansson at oracle.com
Tue Aug 27 07:34:50 UTC 2019
> 26 aug. 2019 kl. 22:48 skrev Kim Barrett <kim.barrett at oracle.com>:
>> On Aug 26, 2019, at 2:29 PM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
>>> 26 aug. 2019 kl. 17:42 skrev Kim Barrett <kim.barrett at oracle.com>:
>>>> On Aug 26, 2019, at 4:52 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
>>>> I really like the cleanups you’ve done in this area of the code base and this one is no exception. Looks good, just one question around the different G1ConcRefinement-flags (threshold and zones). Couldn’t we make these be number of cards and get rid of the buffers_to_cards conversion in g1ConcurrentRefine.cpp?
>>> Those are product options; changing their semantics like that is not so easy.
>> True, but I think it is something we want to do in the longer run so maybe creating an enhancement for it to track it?
> Maybe, and maybe not.
> If expressed in card counts, some of these numbers probably ought to
> have minimum values that are some multiple of the buffer size (which
> is also controlled by a CLA, G1UpdateBufferSize). Having the external
> value be in buffers, internally scaled by the buffer size, might have
> usability benefits. And suggesting or encouraging apparently higher
> precision by having options in card counts isn't necessarily useful.
> Also, some of those options might go away entirely. I did some
> experimental work a while ago on improving the adaptive controllers in
> this area, which I want to get back to. Some of those options were no
> longer relevant or even interfering with that work.
> To make such a change would involve adding new options that have card
> units (and probably have worse / longer names than the existing names
> that are already a mouthful). I'd probably want to be experimental
> because of the above mentioned possibility of elimination or other
> changes. Deprecate the old buffer-based options. Add code to reject
> explicit use of both. Retain the new code to convert buffer options
> to card units. Somewhere down the road remove the deprecated options,
> and perhaps upgrade to product the new options; or not, if some go
> away entirely.
> So I'd prefer they were left alone until such time as we have a better
> understanding of what we actually want / need here.
Sounds like a good plan, and let’s hope we can figure out some good names :)
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