RFR (S): 8014971: Minor code cleanup of the freelist management
Bengt Rutisson
bengt.rutisson at oracle.com
Tue May 21 13:35:44 UTC 2013
Hi all,
While fixing 'JDK-7066063: CMS: "Conservation Principle" assert failed'
I made some code cleanups in the code I was browsing. I didn't want to
mix these changes in with the bug fix, so I'm submitting this review for
those changes. Could I have a couple of reviews of this small cleanup?
http://cr.openjdk.java.net/~brutisso/8014971/webrev.00/
Here is what I did:
- Removed the unused constructors for FreeList and AdaptiveFreeList
- Removed unnecessary NULL check after call to global operator new. The
new operator already checks the allocation and exits the VM if it fails.
- Removed unused old_end variable in
ConcurrentMarkSweepGeneration::grow_by().
- Fixed a possible bug in
CompactibleFreeListSpace::addChunkToFreeListsAtEndRecordingStats()
The last fix may require some explanation. In the constructor for
CompactibleFreeListSpace() we set up the _indexedFreeListParLocks array.
But we only set it up if ParallelGCThreads > 0, so if we are single
threaded the locks are unintialized (not even NULL, just random values).
In CompactibleFreeListSpace::addChunkToFreeListsAtEndRecordingStats() we
use these locks but we don't check for ParallelGCThreads > 0. We only
check the chunk size to see if there is a chance that the chunk may end
up in the smaller buckets. This will fail if ParallelGCThreads = 0.
This bug is benign since
CompactibleFreeListSpace::addChunkToFreeListsAtEndRecordingStats() is
only used when we grow or shrink the generation. This is always done
with os::vm_allocation_granularity() which is larger than
SmallForDictionary so we will never enter the dangerous code path.
However, if someone in the future either increases the value of
SmallForDictionary or uses a smaller alignment for the generation sizing
we might hit this problem. So, I figured it is worth leaving the code
but making sure that it works properly.
Thanks,
Bengt
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