[jdk11u-dev] RFR: 8253638: Cleanup os::reserve_memory and remove MAP_FIXED [v2]

[Thomas Stuefe]

On Tue, 2 Nov 2021 07:10:34 GMT, Vladimir Kempik <vkempik at openjdk.org> wrote:

>> Hello, please review this backport of JDK-8253638  to jdk11u-dev, its a prerequest for JDK-8255254 ( and MAP_JIT support as well) which is mac-aarch64 backport prerequest
>
> Vladimir Kempik has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix up windows

Hi Vladimir,

I am concerned a bit because this code changed a lot over the last years due to this issue and the https://bugs.openjdk.java.net/browse/JDK-8256155 which needed a bunch of preparatory patches, and due to the fact that we unified coding in os_posix. And on JDK11 we have more and older OSes.

Which backports would be required to get MAP_JIT to work? I see at the very least:

https://bugs.openjdk.java.net/browse/JDK-8255254 Split os::reserve_memory and os::map_memory_to_file interfaces
https://bugs.openjdk.java.net/browse/JDK-8234930 Use MAP_JIT when allocating pages for code cache on macOS

do you think there would be more?

I assume this is not a clean backport, right? Since you had to at least add Solaris support? Any other changes you had to do? Did you try building it (I realize not everyone has Solaris, so I'm just curious what tests you have already run)?

Before we go down this route, I wonder whether there is a simple non-invasive hack to fix the MAP_JIT issue for MacOS only on JDK11 without backporting all those changes.

Pinging @AntonKozlov :)

Cheers, Thomas

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PR: https://git.openjdk.java.net/jdk11u-dev/pull/574