RFR: 8251330: Reorder CDS archived heap to speed up relocation [v2]

[Matias Saavedra Silva]

> We should reorder the archived heap to segregate the objects that don't need marking. This will save space in the archive and improve start-up time
> 
> This patch reorders the archived heap to segregate the objects that don't need marking. The leading zeros present in the bitmaps thanks to the reordering can be easily removed, and this the size of the archive is reduced.
> 
> Given that the bitmaps are word aligned, some leading zeroes will remain. Verified with tier 1-5 tests.
> 
> Metrics, courtesy of @iklam :
> ```calculate_oopmap: objects = 15262 (507904 bytes, 332752 bytes don't need marking), embedded oops = 8408, nulls = 54
> Oopmap = 15872 bytes
> 
> calculate_oopmap: objects = 4590 (335872 bytes, 178120 bytes don't need marking), embedded oops = 46487, nulls = 29019
> Oopmap = 10496 bytes
> 
> (332752 + 178120) / (507904 + 335872.0) = 0.6054592688106796 
> More than 60% of the space used by the archived heap doesn't need to be marked by the oopmap. 
> 
> $ java -Xshare:dump -Xlog:cds+map | grep lead
> [3.777s][info][cds,map] - heap_oopmap_leading_zeros: 143286
> [3.777s][info][cds,map] - heap_ptrmap_leading_zeros: 50713
> 
> So we can reduce the "bm" region by (143286 + 50713) / 8 = 24249 bytes.
> 
> Current output:
> $ java -XX:+UseNewCode -Xshare:dump -Xlog:cds+map | grep lead 
> [5.339s][info][cds,map] - heap_oopmap_leading_zeros:      26
> [5.339s][info][cds,map] - heap_ptrmap_leading_zeros:      8

Matias Saavedra Silva has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 29 additional commits since the last revision:

 - Added helper function
 - Merge branch 'master' into reorder_archive_heap_8251330
 - Removed commented code
 - Adjusted word alignment in slice method
 - Merge branch 'master' into reorder_archive_heap_8251330
 - Merge branch 'master' into reorder_archive_heap_8251330
 - Fixed sorting of equal rank objs
 - Only set zeros once
 - Improved setting leading zeros
 - Merge branch 'master' into reorder_archive_heap_8251330
 - ... and 19 more: https://git.openjdk.org/jdk/compare/8c9a72c9...bb1409dd

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17350/files
  - new: https://git.openjdk.org/jdk/pull/17350/files/bf759be8..bb1409dd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17350&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17350&range=00-01

  Stats: 31732 lines in 903 files changed: 13751 ins; 11726 del; 6255 mod
  Patch: https://git.openjdk.org/jdk/pull/17350.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17350/head:pull/17350

PR: https://git.openjdk.org/jdk/pull/17350