RFR: 8325670: GenShen: Allow old to expand at end of each GC

[Y. Srinivas Ramakrishna]

On Mon, 19 Feb 2024 20:50:46 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

> ... covering that one case of SOERP sending the value to NaN but not otherwise bounding it and allowing it to grow arbitrarily large and wrapping around).

I realize that there is in fact a natural bound to that value when SOERP < 100, viz. when it's 99 (since it's not a float): `young_reserve * 99/(100-99)`, i.e. `99 * young_reserve`. I guess the simpler thing to do then is to just avoid this completely and declare `ShenandoahEvactReserve` to `range(1,99)` and be done, throwing awy the protection for the lone case of `SOERP=100` -- after all we don't allow `SOERP=0`, so by symmetry it looks like we shouldn't allow 100 either, just `range(1,99)`.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/394#discussion_r1495116929