RFR: 8319795: Static huge pages are not used for CodeCache

[Thomas Stuefe]

On Thu, 9 Nov 2023 15:20:26 GMT, Evgeny Astigeevich <eastigeevich at openjdk.org> wrote:

> This is a fix of a regression introduced by [JDK-8261894](https://bugs.openjdk.org/browse/JDK-8261894).
> After JDK-8261894, `os::can_execute_large_page_memory()` returns `true` only if `UseTransparentHugePages` is true. As CodeCache uses `os::can_execute_large_page_memory()` when it detects a page size, CodeCache cannot use static huge pages (`UseTransparentHugePages` is `false`) anymore after the change.
> Before JDK-8261894, `os::can_execute_large_page_memory()` returned `true`  when either `UseTransparentHugePages` or `UseHugeTLBFS` was true.
> 
> After JDK-8261894, `XX:+UseLargePages XX:-UseTransparentHugePages` means to use static huge pages: aka `UseHugeTLBFS` is `true`. If `UseLargePages` is not set to `true` via the option, it will be set to `true` if `UseTransparentHugePages` is `true`.
> 
> `os::can_execute_large_page_memory()` is modified to return `UseLargePages`. A regression gtest  is added.
> 
> Tested fastdebug and release builds:
> - [x] tier1
> - [x] gtest
> - [x] test/hotspot/jtreg/gtest/LargePageGtests.java

Good catch.

But the whole function makes no sense anymore. It was used because System V shared memory could not be set executable. We don't use that anymore, so any large page memory is executable. You could return true now (returning UseLargePages makes not that much sense).

But no other platform has restrictions like that. Windows has large pages, and they can be set executable. Now Linux is the same. BSD/MacOs and AIX don't use large pages. So I think we can just completely remove that function.

We should have a regression test for this...

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PR Comment: https://git.openjdk.org/jdk/pull/16582#issuecomment-1804140006
PR Comment: https://git.openjdk.org/jdk/pull/16582#issuecomment-1804142578