RFR: 8253594: Remove CollectedHeap::supports_tlab_allocation

[Stefan Johansson]

On Thu, 24 Sep 2020 11:06:24 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> CollectedHeap::supports_tlab_allocation always returns true, and is only used in an assert. I propose that we remove it.
> 
> GenCollectedHeap is the only implementation that didn't trivially return true. Instead it deferred the question to the
> young gen, which after the CMS removal is only DefNew. I updated the GenCollectedHeap tlab functions to assert that the
> young gen always supports TLABs. This could be taken even further, and the Generation::supports_tlab_allocation()
> function could be entierly removed, but that requires that we change GenCollectedHeap to be explicit about the types
> for _young_gen and _old_gen. So, I left  that part for another day.

Marked as reviewed by sjohanss (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/335