RFR: JDK-8322943: runtime/CompressedOops/CompressedClassPointers.java fails on AIX [v2]

[Joachim Kern]

On Tue, 27 Feb 2024 05:57:42 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> > I don't think a local test fix makes sense. After all it is a real issue that os::attempt_reserve_memory_between() is using 4K alignment when we try to allocate 256M shmat memory. We could do a temporary #ifdef AIX solution in that function.
> 
> That is a good point. And a good compromise.
> 
> @JoKern65 can you try this:
> 
> ```
> diff --git a/src/hotspot/share/runtime/os.cpp b/src/hotspot/share/runtime/os.cpp
> index 5d6c1fa69ca..34a708e1cdc 100644
> --- a/src/hotspot/share/runtime/os.cpp
> +++ b/src/hotspot/share/runtime/os.cpp
> @@ -1892,7 +1892,15 @@ char* os::attempt_reserve_memory_between(char* min, char* max, size_t bytes, siz
>    char* const absolute_max = (char*)(NOT_LP64(G * 3) LP64_ONLY(G * 128 * 1024));
>    char* const absolute_min = (char*) os::vm_min_address();
>  
> -  const size_t alignment_adjusted = MAX2(alignment, os::vm_allocation_granularity());
> +  const size_t system_allocation_granularity =
> +#ifdef AIX
> +  // AIX is the only platform that uses System V shm for reserving virtual memory. As long as we
> +  // have not fixed os::vm_allocation_granularity(), hard-code allocation granularity of SHMLBA here.
> +      SHMLBA;
> +#else
> +      os::vm_allocation_granularity();
> +#endif
> +  const size_t alignment_adjusted = MAX2(alignment, system_allocation_granularity);
> ```

Yes, I will try that, but one question. Is the following code snipit an example for the incorrect use of vm_allocation_granularity or did I understand something wrong?


ReservedSpace::ReservedSpace(char* base, size_t size, size_t alignment, size_t page_size,
                             bool special, bool executable) : _fd_for_heap(-1) {
  assert((size % os::vm_allocation_granularity()) == 0,
         "size not allocation aligned");
  initialize_members(base, size, alignment, page_size, special, executable);
}

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PR Comment: https://git.openjdk.org/jdk/pull/17708#issuecomment-1965911543