RFR: 8272807: Permit use of memory concurrent with pretouch [v3]

[Aleksey Shipilev]

On Tue, 8 Feb 2022 10:25:43 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> [Trying again, after a couple previous proposals.]
>> 
>> Please review this change to os::pretouch_memory to permit use of the memory
>> being pretouched concurrently with the pretouch operation.  This will allow
>> future changes that can make use of such overlap.
>> 
>> Testing:
>> mach5 tier1-3 with -XX:+AlwaysPreTouch.
>> 
>> Verified no performance impact by comparing startup times with Epsilon GC and
>> -XX:+AlwaysPretouch on a large enough heap that the pretouch takes a
>> significant amount of time.  Tested on both linux-x64 and linux-aarch64.
>> 
>> None of these test concurrent use; that will wait for future changes that use
>> the new feature.
>
> Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:
> 
>   change loop termination test

Marked as reviewed by shade (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/7343