Re: ZGC: RFR: 8207843: HSDB cannot show Object Histogram when ZGC is working

[Yasumasa Suenaga]

Hi Sharath,

Thank you for your comment!

On 2018/08/08 13:35, Sharath Ballal wrote:

Hi Yasumasa,

These comments may not make sense now that Per told that this way of iterating 
the heap doesn’t work for ZGC.  But I am still giving them since I went through 
the changes.

I think we need to work after clarifying class unloading in ZGC.
So I will fix your comment later.

http://cr.openjdk.java.net/~ysuenaga/JDK-8207843/webrev.00/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/z/ZPage.java.udiff.html

+    public int refcount() {
+        return topField.getJInt(addr);
+    }
+

I think you wanted to return "refcountField.getJInt(addr)" here.

You are correct! I'll fix it.

http://cr.openjdk.java.net/~ysuenaga/JDK-8207843/webrev.00/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/gc/z/ZAddressRangeMapForPageTable.java.frames.html

   71     long size() {
   72         return ZGlobals.ZAddressOffsetMax >>> ZGlobals.ZPageSizeMinShift;
   73     }

I am not clear about this unsigned right shift, how does this give the size ?  
Also ZGlobals.ZPageSizeMinShift can be replaced by AddressRangeShift.

This method comes from ZAddressRangeMap<T, AddressRangeShift>::size() in 
zAddressRangeMap.inline.hpp .
ZAddressOffsetMax is declared as size_t, so we need to treat it as unsigned 
value.


Thanks,

Yasumasa

Thanks,
Sharath


-----Original Message-----
From: Yasumasa Suenaga [mailto:yasue...@gmail.com]
Sent: Thursday, July 26, 2018 7:22 PM
To: serviceability-dev@openjdk.java.net; zgc-...@openjdk.java.net; 
hotspot-gc-dev
Subject: ZGC: RFR: 8207843: HSDB cannot show Object Histogram when ZGC is 
working

CC'ing to hotspot-gc-dev


On 2018/07/26 21:30, Yasumasa Suenaga wrote:

PING: Could you review it?

    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8207843/webrev.00/

Yasumasa


On 2018/07/19 23:03, Yasumasa Suenaga wrote:

Hi all,

Please review this webrev.

       JBS: https://bugs.openjdk.java.net/browse/JDK-8207843
    webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8207843/webrev.00/

I encountered AssertionFailure when I attached HSDB to the process which is 
working with ZGC as below:

sun.jvm.hotspot.utilities.AssertionFailure: Unexpected CollectedHeap type: 
sun.jvm.hotspot.gc.z.ZCollectedHeap
      at jdk.hotspot.agent/sun.jvm.hotspot.utilities.Assert.that(Assert.java:32)
      at 
jdk.hotspot.agent/sun.jvm.hotspot.oops.ObjectHeap.collectLiveRegions(ObjectHeap.java:448)
      at 
jdk.hotspot.agent/sun.jvm.hotspot.oops.ObjectHeap.iterate(ObjectHeap.java:173)
      at jdk.hotspot.agent/sun.jvm.hotspot.HSDB$VisitHeap.run(HSDB.java:1741)
      at 
jdk.hotspot.agent/sun.jvm.hotspot.utilities.WorkerThread$MainLoop.run(WorkerThread.java:70)
      at java.base/java.lang.Thread.run(Thread.java:832)

ObjectHeap#collectLiveRegions() branches by instance type of CollectedHeap. 
However it does not support ZCollectedHeap.
So I add ZCollectedHeap to it and add some methods to iterate ZPageTable.


Thanks,

Yasumasa