[9] RFR(M) 8041984: CompilerThread seems to occupy all CPU in a very rare situation

[Aleksey Shipilev]

I remember chasing the similar issue here:
 https://bugs.openjdk.java.net/browse/JDK-8057127

...but never got a chance to pinpoint the actual method that causes EA
to explode. I will take a look again once your fix is committed.

-Aleksey.

On 11.10.2014 07:41, Vladimir Kozlov wrote:
> https://bugs.openjdk.java.net/browse/JDK-8041984
> http://cr.openjdk.java.net/~kvn/8041984/webrev/
> 
> Next method puts C2's EA to its knees:
> 
> com.graphhopper.coll.GHLongIntBTree$BTreeEntry::put()
> 
> https://github.com/karussell/graphhopper/blob/master/core/src/main/java/com/graphhopper/coll/GHLongIntBTree.java
> 
> 
> It shows that current EA connection graph build code is very inefficient
> when a graph has a lot of connections (edges).
> 
> With inlining the BTreeEntry::put() method has about 100 allocations
> from which about 80 are arrays allocations. Most of them are object
> arrays which are generated by Arrays.copyOf(). After number of edges in
> EA Connection Graph reaches about 50000 it takes more then 1 sec to find
> all nodes which reference an allocation.
> 
> Current EA code has bailout by timeout from graph building code. But the
> timeout (30 sec for product VM) is checked only after all object nodes
> are processed. So it may take > 2 mins before EA is aborted:
> 
> <phase name='connectionGraph' nodes='18787' live='10038' stamp='4.417'>
> <connectionGraph_bailout reason='reached time limit'/>
> <phase_done name='connectionGraph' nodes='18787' live='10038'
> stamp='150.967'/>
> 
> Also ConnectionGraph::add_java_object_edges() method does not check the
> presence of a node when it adds new one to the worklist (in
> add_to_worklist() method). Which leads to hundreds MB of used by EA
> memory when BTreeEntry::put() is processed.
> 
> To address issues new timeout checks were added.
> New _pidx index field is added to graph's nodes and VectorSet is used to
> reduce size of worklist in add_java_object_edges() method.
> 
> Escaping node CreateEx is mapped phantom_obj to reduce number of process
> objects in connection graph. We do the same for other escaping objects.
> 
> Tested with graphhopper server application:
> 
> <phase name='connectionGraph' nodes='18787' live='10038' stamp='6.829'>
> <connectionGraph_bailout reason='reached time limit'/>
> <phase_done name='connectionGraph' nodes='18787' live='10038'
> stamp='22.355'/>
> 
> Thanks,
> Vladimir


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