[jdk25u-dev] RFR: 8370572: Cgroups hierarchical memory limit is not honored after JDK-8322420

[Paul Hohensee]

On Thu, 11 Dec 2025 11:38:27 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> Unclean backport of JDK-8370572 since JDK-8292984 is not in 25u (a cleanup patch). That change basically renames `phys_mem` to `upper_bound`. Not really critical to get JDK-8292984 into 25u. What's more, the changes in this patch have the changes done in JDK tip with JDK-8365606 of moving the `if (uses_hierarchy)` inside the branch where the limit is larger than the host limit (upper bound limit). This is the more defensive fix to not fall into the `else` branch should `memory.use_hierarchy` see a `0`.
> 
> Please review!
> 
> Testing:
> - [x] GHA
> - [x] Container tests on Linux x86_64 on cgroups v1 including the test from JDK-8370966 ([see dependent PR](https://github.com/openjdk/jdk25u-dev/pull/77)). Also checked container tests on cgroups v2 for sanity. This patch is a no-op there.

Marked as reviewed by phh (Reviewer).

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PR Review: https://git.openjdk.org/jdk25u-dev/pull/76#pullrequestreview-3569679309