RFR: 8272083: G1: Record iterated range for BOT performance during card scan [v4]

[Stefan Johansson]

On Wed, 13 Oct 2021 08:59:21 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> > One question, how do we make sure that as much as possible of the BOT is updated concurrently before the next GC?
> 
> The idea is to make sure that new cards into areas not yet updated are processed in an expedited way (i.e. "immediately") - since card processing automatically updates the BOTs, we only need to make sure they are processed without waiting for the regular mechanism to kick in.
>

Ok, good, because just using the normal refinement mechanism might be to slow. 
 
> One could also enqueue the "first" card in newly allocated PLABs in special queues that are processed with priority. There are a few options as usual, and we would certainly like to find a good one wrt to several aspects.
> 

I agree there are few different ways to solve this, and we should seek to find the best one both from a performance and maintainability perspective. 

Stefan

> Thomas

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PR: https://git.openjdk.java.net/jdk/pull/5039