RFR: 8255234: ZGC: Bulk allocate forwarding data structures [v2]

[Stefan Karlsson]

On Fri, 23 Oct 2020 08:11:55 GMT, Per Liden <pliden at openjdk.org> wrote:

>> Allocation of forwarding data structures (ZForwarding/ZForwardingEntry instances) can generate a lot of calls to new/malloc if the number of pages in the relocation set is large. This can make the "Concurrent Select Relocation Set" phase long. By bulk allocating a single piece of memory and then placement new() all objects into that memory we can speed this phase up quite a bit.
>> 
>> During relocation set selection we keep track of the number of ZForwardingEntry instances we will need for the selected relocation set. The ZForwardingAllocator is then initialized to have enough room for all the relocation set array, all ZForwarding instances, and all ZForwardingEntry instances. Objects are then placement new()'d using into the memory allocated by the ZForwardingAllocator.
>> 
>> This patch was joint work with Albert (ayang).
>
> Per Liden has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Assert that allocations never fail

Looks good. Thanks for accepting the proposed changes. (Some old comments might have been sent by the mlbridge. I've delete those in the PR)

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Marked as reviewed by stefank (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/804