RFR (M) 8164921: Memory leaked when instrumentation.retransformClasses() is called repeatedly

[serguei.spitsyn at oracle.com]

Hi Coleen,


Just wanted to share a couple of comments I have so far.


http://cr.openjdk.java.net/~coleenp/8164921.01/webrev/src/share/vm/memory/metaspace.cpp.frames.html

302 debug_only(GrowableArray<Metablock*>* _all_blocks);
855 DEBUG_ONLY(_all_blocks = new (ResourceObj::C_HEAP, mtClass) 
GrowableArray<Metablock*>(100, true)); 863 DEBUG_ONLY(delete 
_all_blocks;) 891 
DEBUG_ONLY(_all_blocks->remove((Metablock*)new_block)); 908 
DEBUG_ONLY(_all_blocks->remove((Metablock*)free_block)); 922 
DEBUG_ONLY(_all_blocks->remove((Metablock*)new_block));

   Not clear, why different macros debug_only() is used at L302.   Could 
it be DEBUG_ONLY as well?

  866 void BlockFreelist::return_block(MetaWord* p, size_t word_size) {
  867   Metablock* free_chunk = ::new (p) Metablock(word_size);
868 if (word_size < SmallBlocks::small_block_min_size()) {
869 // Dark matter
870 return; 871 } else if (word_size < 
SmallBlocks::small_block_max_size()) {

  In case of dark matter the free_chunk is leaked.  It is better to 
rearrange the fragment to something like this:

  void BlockFreelist::return_block(MetaWord* p, size_t word_size) {
if (word_size < SmallBlocks::small_block_min_size()) {
return; // Dark matter
}
Metablock* free_chunk = ::new (p) Metablock(word_size); if (word_size < 
SmallBlocks::small_block_max_size()) {

  886 MetaWord* BlockFreelist::get_block(size_t word_size) {
887 if (word_size < SmallBlocks::small_block_max_size() && 
small_blocks()->list_at(word_size).count() > 0) {
  . . .
892 return new_block;
893 }
894
895 if (word_size < BlockFreelist::min_size()) {
  896     // Dark matter.  Too small for dictionary.
  897     return NULL;
  898   }

   It'd be better to reorder the fragments 887-893 and 895-898. Thanks, 
Serguei On 9/30/16 12:02, Coleen Phillimore wrote:
> Summary: Return Metablocks smaller than dictionary's dark matter. This 
> change contributed by Jon Masamitsu and myself.  To reclaim "dark 
> matter" this change adds an array of small blocks by size, created 
> lazily, to return Metablocks smaller than the BinaryTreeDictionary 
> entry's minimum size.   This change also fixed a bug in small object 
> double free and adds debugging code to check for this case. With this 
> change, the submitted test case runs indefinitely.   Also passed rbt 
> tier 1-5 testing. open webrev at 
> http://cr.openjdk.java.net/~coleenp/8164921.01/webrev bug link 
> https://bugs.openjdk.java.net/browse/JDK-8164921 Thanks, Coleen and Jon