RFR: 8324781: runtime/Thread/TestAlwaysPreTouchStacks.java failed with Expected a higher ratio between stack committed and reserved [v2]

[Stefan Karlsson]

On Mon, 8 Apr 2024 06:57:23 GMT, Liming Liu <duke at openjdk.org> wrote:

>> The testcase failed on Oracle CI since JDK-8315923. The root cause is that Oracle CI runs Linux-5.4.17-UEK where the value of MADV_POPULATE_WRITE (23) is used as MADV_DONTEXEC which is not supported by upstream. This PR solves the testcase failure by checking versions of kernels first, and checking the availability of MADV_POPULATE_WRITE when they are not older than 5.14.
>
> Liming Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Exit early in os::pd_pretouch_memory and generate a warning when user turns on UseMadvPopulteWrite when not supported

Thanks for the updates. I have a few more comments.

src/hotspot/os/linux/os_linux.cpp line 4838:

> 4836:     if (!FLAG_IS_DEFAULT(UseMadvPopulateWrite) && !supportMadvPopulateWrite)
> 4837:       warning("Platform is supposed not to support MADV_POPULATE_WRITE, "
> 4838:               "disabling using it to pretouch (-XX:-UseMadvPopulateWrite)");

I don't see the code that disables UseMadvPopulateWrite. Is it missing?

The warning message is a bit awkward. Could it be changed to something like: "Platform does not support MADV_POPULATE_WRITE, disabling using it to pretouch memory (-XX:-UseMadvPopulateWrite)"

Could you also make sure to use `{}` even for single statement if blocks?

-------------

Changes requested by stefank (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18592#pullrequestreview-1985713198
PR Review Comment: https://git.openjdk.org/jdk/pull/18592#discussion_r1555391564