On Fri, 25 Aug 2023 02:54:05 GMT, David Holmes <dhol...@openjdk.org> wrote:
> As `AlwaysPreTouch` is false by default, and we don't explicitly turn it on > for CI testing, what tests will actually be affected by this change? And for > applications that already enable `AlwaysPreTouch` (would they?) what impact > might this have e.g. on startup? In the CR I mentioned the following was added as part of the fix done in [JDK-8293563](https://bugs.openjdk.org/browse/JDK-8293563) (which solves this same issue for the ZGC heap): public static String getAlwaysPretouchArg(boolean withCore) { // macosx-aarch64 has an issue where sometimes the java heap will not be dumped to the // core file. Using -XX:+AlwaysPreTouch fixes the problem. if (withCore && Platform.isOSX() && Platform.isAArch64()) { return "-XX:+AlwaysPreTouch"; } else { return "-XX:-AlwaysPreTouch"; } } So this bit of code will make sure that all the SA core file tests use AlwaysPreTouch on macosx-aarch64. As for performance impact. I'm not certain and I'm also not to certain of the use case for AlwaysPretouch. As far as I can tell in was introduced by [JDK-6806090](https://bugs.openjdk.org/browse/JDK-6806090) and seems it was actually added to help with performance, although I'm not sure how. The CDS archive tends to be small compared with the java heap, so I would think the relative impact would be small. Also unclear is how much of the archive is likely to get mapped in on startup anyway. Perhaps @iklam can add some insight. ------------- PR Comment: https://git.openjdk.org/jdk/pull/15423#issuecomment-1692749815
