RFR: 8236847: CDS archive with 4K alignment unusable on machines with 64k pages

[Thomas Stuefe]

On Tue, 23 Feb 2021 02:51:01 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Hi, Please review
>>   Usually most OSes are configured with page size of 4K, but some others are configured with 64K. If jdk binary is built on 4K platform and run on different configured platforms, CDS fails to be loaded due to region alignment mismatch:
>>   Unable to map CDS archive -- os::vm_allocation_granularity() expected: 4096 actual: 65536
>>   This change uses 64K as region alignment if OS page size is less than 64K. For most of the current OSes, means always use 64K as file map region alignment.
>>    The archive size will increase about 300K due to the change. 
>>    Tests: tier1-4
>>               Run MacOS/X64 binary on MacOS/aarch64 
>> 
>>    Thanks
>>    Yumin
>
> Changes requested by iklam (Reviewer).

Should we only use this on platforms where one can have different base page sizes *on the same platform*? Since the only one of our platforms I know where this could even be an issue are aarch, and possibly AIX.

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PR: https://git.openjdk.java.net/jdk/pull/2651