RFR: 8252103: Parallel heap inspection for ParallelScavengeHeap [v4]

[Stefan Johansson]

On Mon, 19 Oct 2020 13:09:34 GMT, Lin Zang <lzang at openjdk.org> wrote:

>> - Parallel heap iteration support for PSS
>> - JBS:  https://bugs.openjdk.java.net/browse/JDK-8252103
>
> Lin Zang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.

Took a second look today and found two additional problems. 

I would also be interested in what kind of testing you've done with this patch.

src/hotspot/share/gc/parallel/psOldGen.cpp line 199:

> 197: 
> 198:   // iterate objects in block.
> 199:   HeapWord* end = MIN2(top, begin + _iterate_block_size);

`_iterate_block_size` is a size in bytes (or at least you use it like a size in bytes when calculating the number of blocks), so before you can add it you need to convert it to a size in words like this:

Suggestion:

  size_t block_word_size = _iterate_block_size / HeapWordSize;
  HeapWord* begin = bottom + block_index * block_word_size;
 
  assert((block_word_size % (ObjectStartArray::block_size)) == 0,
          "BLOCK SIZE not a multiple of start_array block");
 
  // iterate objects in block.
  HeapWord* end = MIN2(top, begin + block_word_size);

-------------

Changes requested by sjohanss (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/25