RFR: 8334371: [AIX] Beginning with AIX 7.3 TL1 mmap() supports 64K memory pages [v5]

[Martin Doerr]

On Mon, 1 Jul 2024 13:37:54 GMT, Joachim Kern <jkern at openjdk.org> wrote:

>> Beginning with AIX 7.3 TL1 mmap() supports 64K memory pages. As an enhancement, during the initialization of the VM the availability of this new feature is examined. If the 64K pages are supported the VM will use mmap() with 64K pages instead of shmget()/shmat() with 64K pages due to the bad 256M alignment of shmget()/shmat().
>
> Joachim Kern has updated the pull request incrementally with one additional commit since the last revision:
> 
>   following Martins proposals

src/hotspot/share/runtime/os.cpp line 1927:

> 1925:   // The logic here is dual to the one in pd_reserve_memory in os_aix.cpp
> 1926:   const size_t system_allocation_granularity =
> 1927:     AIX_ONLY(os::vm_page_size() == 4*K ? 4*K : os::Aix::supports_64K_mmap_pages() ? 64*K : 256*M)

Please add braces or rewrite it. Does
`AIX_ONLY( (!os::Aix::supports_64K_mmap_pages() && os::vm_page_size() == 64*K) ? 256*M : ) os::vm_allocation_granularity()` work?

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PR Review Comment: https://git.openjdk.org/jdk/pull/19771#discussion_r1661108094