RFR: 8232604: ZGC: Make ZVerifyViews mapping and unmapping precise

[Erik Österlund]

Hi Stefan,

Looks good.

Thanks,
/Erik

On 2019-10-24 18:36, Stefan Karlsson wrote:
> Hi all,
>
> Please review this patch to make the ZVerifyViews mapping and 
> unmapping precise.
>
> https://cr.openjdk.java.net/~stefank/8232604/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8232604
>
> Today, when the ZVerifyViews flag is turned on, we unmap all bad 
> views. The intention is to catch stray-pointer bugs.
>
> The current implementation takes a short-cut and unmap all memory en 
> masse. This works for Linux, but not on Windows, where we must be 
> precise in what we unmap.
>
> There are three places where allocated pages are registered today:
> - In the page table - actively used
> - In the page cache - free pages waiting to be used
> - In-flight from the alloc queue
>
> The proposed patch registers all satisfied alloc requests, lets the 
> requesting threads deregister the satisfied request when the page is 
> received, and makes sure that the GC visits all in-flight satisfied 
> alloc requests when it performs the ZVerifyViews flip.
>
> Thanks,
> StefanK