[rvm-research] Failure implementing a Mark-Sweep plus Semispace composite

Hi All,

I am having problems with a new collector I am trying to build that extends the traditional generational semispace collector in JikesRVM with another mature space that is an instance of the MarkSweepSpace (MS). The plan is as follows. Nursery survivors always evacuate to the active mature semispace. Objects are copied between the two mature semispaces as usual. From time to time, a mature collection copies a selection of the live objects out of the mature semispace to MS and vice-versa. A live object in MS is guaranteed to be either marked or forwarded during a mature collection.

Everything works fine as long as there are no copies from MS to the semispace. But if objects are copied from MS to the semispace, then after a few collections, JikesRVM crashes. It appears to me that crash always occur during a collection phase.

I have taken care that the GC header has both forwarding bits and mark bits. The GC header is initialized properly when the object is copied to a space. I updated the masks in MarkSweepSpace appropriately. Also note that the copies between the different spaces always succeed. 

Logically, I am quite convinced that my plan should work correctly. Something is probably missing in the implementation.

Anyone who tired similar things: is there any fundamental limitation to copying objects from a MarkSweep space to a copy space? Other things that I need to take care to make this plan work correctly? Should I provide more details?

A stack dump from one run of a benchmark is appended. Any help or suggestion is greatly appreciated!

Regards,
Shoaib.

scanning 6
scanning 2
scanning 3
scanning 1
hardwareTrapHandler: thread = 0xf5fffb40
JikesRVM: TROUBLE.  Got a signal (Segmentation fault; #11) from outside the VM's address space in thread 0xf5fffb40.
JikesRVM: UNRECOVERABLE trapped signal 11 (Segmentation fault)
handler stack 5cb700
si->si_addr   0x5cb700
cs            0x00000023
ds            0x0000002b
es            0x0000002b
fs            0x00000000
gs            0x00000063
ss            0x0000002b
edi           0x7001d020
esi -- PR/VP  0x70008414
ebp           0x71011b1c
esp -- SP     0x70c9dc48
ebx           0x74b3a2f3
edx           0x71011b1c
ecx           0x7380a050
eax           0x71011b1c
eip           0x005cb700
trapno        0x0000000e
err           0x00000014
eflags        0x00010203
fpregs        f5604150
oldmask       0x00020000
cr2           0x005cb700
fp0 0x00000000000000000000
fp1 0x00000000000000000000
fp2 0x00000000000000000000
fp3 0x00000000000000000000
fp4 0x00000000000000000000
fp5 0x00000000000080004005
fp6 0x00000000000080004019
fp7 0x00000000e30085fc4016
JikesRVM: internal error
-- Stack --
(0x70c9dcb8 19460)   at [0x70c9dcb8, 0x647a9bc2] Lorg/jikesrvm/mm/mmtk/ScanThread; scanFrame(I)Lorg/vmmagic/unboxed/Address; at line 367
(0x70c9dd04 19457)   at [0x70c9dd04, 0x64a207c7] Lorg/jikesrvm/mm/mmtk/ScanThread; scanThreadInternal(Lorg/vmmagic/unboxed/Address;I)V at line 279
(0x70c9dd60 19477)   at [0x70c9dd60, 0x64a209ef] Lorg/jikesrvm/mm/mmtk/ScanThread; startScan(Lorg/mmtk/plan/TraceLocal;ZLorg/jikesrvm/scheduler/RVMThread;Lorg/vmmagic/unboxed/Address;Lorg/vmmagic/unboxed/Address;Lorg/vmmagic/unboxed/Address;Lorg/vmmagic/unboxed/Address;Lorg/vmmagic/unboxed/Address;)V at line 229
   at [0x70c9dd60, 0x64a209ef] Lorg/jikesrvm/mm/mmtk/ScanThread; scanThread(Lorg/jikesrvm/scheduler/RVMThread;Lorg/mmtk/plan/TraceLocal;ZLorg/vmmagic/unboxed/Address;Lorg/vmmagic/unboxed/Address;)V at line 195
(0x70c9ddd0 19475)   at [0x70c9ddd0, 0x6497ad0a] Lorg/jikesrvm/mm/mmtk/ScanThread; scanThread(Lorg/jikesrvm/scheduler/RVMThread;Lorg/mmtk/plan/TraceLocal;Z)V at line 147
(0x70c9ddfc 20814)   at [0x70c9ddfc, 0x6476db36] Lorg/jikesrvm/mm/mmtk/Scanning; computeThreadRoots(Lorg/mmtk/plan/TraceLocal;)V at line 189
(0x70c9de80 9495)   at [0x70c9de80, 0x64790484] Lorg/mmtk/plan/SimpleCollector; collectionPhase(SZ)V at line 62
   at [0x70c9de80, 0x64790484] Lorg/mmtk/plan/generational/GenCollector; collectionPhase(SZ)V at line 126
(0x70c9ded4 9501)   at [0x70c9ded4, 0x64ce1810] Lorg/mmtk/plan/generational/copying/GenCopyCollector; collectionPhase(SZ)V at line 158
(0x70c9df40 7462)   at [0x70c9df40, 0x64ce2549] Lorg/mmtk/plan/Phase; processPhaseStack(Z)V at line 474
(0x70c9df70 7460)   at [0x70c9df70, 0x6479053b] Lorg/mmtk/plan/Phase; beginNewPhaseStack(I)V at line 385
(0x70c9df84 9490)   at [0x70c9df84, 0x6475bcc3] Lorg/mmtk/plan/StopTheWorldCollector; collect()V at line 40
(0x70c9dfa4 9478)   at [0x70c9dfa4, 0x647aa268] Lorg/mmtk/plan/ParallelCollector; run()V at line 50
(0x70c9dfc4 15787)   at [0x70c9dfc4, 0x64e5df4a] Lorg/jikesrvm/mm/mminterface/CollectorThread; run()V at line 80
(0x70c9dffc 21056)   at [0x70c9dffc, 0x0804f795] Lorg/jikesrvm/scheduler/RVMThread; startoff()V at line 2606
JikesRVM: exit 124
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