RFR: 8357445: G1: Time-Based Heap Uncommit During Idle Periods [v10]

[Monica Beckwith]

> **Implements:** https://bugs.openjdk.org/browse/JDK-8357445
> 
> Implement time-based heap uncommit for G1 during idle periods.
> 
> Key changes:
> - Added G1HeapEvaluationTask for periodic heap evaluation
> - Switch from G1ServiceTask to PeriodicTask for improved scheduling
> - Implemented time-based heap sizing policy with configurable uncommit delay
> - Added region activity tracking with last access timestamps
> - Integrated VM_G1ShrinkHeap operation for safe heap shrinking
> - Added new G1 flags: G1UseTimeBasedHeapSizing, G1TimeBasedEvaluationIntervalMillis, G1UncommitDelayMillis, G1MinRegionsToUncommit
> - Added 'sizing' log tag for heap sizing operations
> 
> Comprehensive Test Coverage:
> - Enhanced TestG1RegionUncommit: minimum heap boundaries, concurrent allocation/uncommit scenarios
> - Enhanced TestTimeBasedHeapSizing: humongous object handling, rapid allocation cycles, edge cases
> - Enhanced TestTimeBasedRegionTracking: concurrent region access, lifecycle transition validation
> - Enhanced TestTimeBasedHeapConfig: parameter boundary values, small heap configurations
> 
> This ensures time-based heap uncommit works correctly while maintaining all safety guarantees and test expectations.

Monica Beckwith has updated the pull request incrementally with two additional commits since the last revision:

 - Fix compilation errors after master merge
   
   - Fix syntax error in g1CollectedHeap.cpp (extra closing brace)
   - Update API call from short_term_pause_time_ratio() to short_term_gc_time_ratio()
   
   These fixes resolve compilation issues that occurred after merging with
   upstream master due to API changes in the OpenJDK codebase.
 - 8357445: Address feedback for G1 time-based heap sizing
   
   - Fix indentation in log_debug statement in shrink_helper (suggested by @tschatzl)
   - Change terminology from 'inactive' to 'idle' throughout time-based heap sizing
   - Update flag descriptions in g1_globals.hpp to use 'idle' terminology
   - Fix remaining trailing whitespace in test files
   
   Addresses all outstanding review comments from @tschatzl

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26240/files
  - new: https://git.openjdk.org/jdk/pull/26240/files/504e6d21..c17f5938

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26240&range=09
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26240&range=08-09

  Stats: 44 lines in 8 files changed: 5 ins; 5 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/26240.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26240/head:pull/26240

PR: https://git.openjdk.org/jdk/pull/26240