RFR: 8275426: PretouchTask num_chunks calculation can overflow

[Kim Barrett]

On Mon, 18 Oct 2021 19:27:46 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Please review this change to part of the calculation of the number of
>> threads to apply to a PretouchTask when using a gang of worker threads.
>> 
>> The previous calculation of the number of chunks in the range to be touched
>> can overflow in the numerator.  (This may only be a realistic problem on
>> 32bit platforms.  On 64bit platforms the value constraint on the chunk size
>> and plausible or architectural limits on the size of the range probably
>> prevent such overflow from occurring.)
>> 
>> Testing:
>> mach5 tier1
>> Locally (linux-x64) ran with logging of the pretouch parameters enabled,
>> with various chunk sizes configured, and hand-checked the logged values.
>
> Marked as reviewed by ayang (Reviewer).

Thanks @albertnetymk and @tschatzl for reviews.

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PR: https://git.openjdk.java.net/jdk/pull/5993