RFR: 8359947: GenShen: use smaller TLABs by default [v2]

[Kelvin Nilsen]

On Wed, 18 Jun 2025 16:39:42 GMT, Paul Hohensee <phh at openjdk.org> wrote:

> What's the rationale for using a fraction of the region size as a possible maximum TLAB size? Region size seems unrelated to thread object allocation demand.

Region size is generally proportional to total heap size.  If we have larger heap sizes, we have more abundant memory, and can generally afford to be "slightly" more generous in apportionment of memory between threads.  But we do this within limits.

The initial TLAB size is never made smaller than 32KB and the max TLAB size is never made larger than 256KB.

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PR Comment: https://git.openjdk.org/jdk/pull/25423#issuecomment-2985016769