java - How to find out where exact young/old gen is located in memory? -

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recently able object's address using sun.misc.unsafe class.

and trying find programmatically actual generation object located. want know starting , ending points of each generation. if java (oracle jvm) provides tools resolve issue? believe not, since different gcs require different memory structures (e.g. g1), , makes task more interesting :)

what want know here couple of numbers representing borders of generations in memory, this:

   young gen: start point - 8501702198                  end point   - 9601256348

would love hear craziest ideas black magic allows determine different generation areas placed in memory.

this possible hotspot jvm though somehow complicated.

the key idea use vmstructs - information hotspot internal constants , types embedded right jvm shared library.

for example, parallelscavengeheap::_young_gen vm global variable contains pointer psyounggen structure has _virtual_space member boundaries of parallel collector's young generation. similarly, gencollectedheap::_gch global points structure describing cms collector generations.

i've made proof-of-concept project demonstrate usage of vmstructs. pure java, no libraries required, relies on undocumented jdk internals , may not work on java versions. i've tested on jdk 8u40 , jdk 7u80 on windows , linux.


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