RFR: 8036703: Add trace event with statistics for the metaspace chunk free lists

[Mikael Gerdin]

Hi Erik,

On Wednesday 12 March 2014 17.04.26 Erik Helin wrote:
> Based on feedback from Mikael and StefanK, I've reworked the patch to
> put the ChunkFreeListSummaries in the class MetaspaceSummary.
> 
> Please see the new version at:
> http://cr.openjdk.java.net/~ehelin/8036703/webrev.03/

I think this version is much better!
Just a small issue:

collectedHeap.cpp
  99 
 100   const MetaspaceChunkFreeListSummary& ms_chunk_free_list_summary =
 101     MetaspaceAux::chunk_free_list_summary(Metaspace::ClassType);
 102   const MetaspaceChunkFreeListSummary& class_chunk_free_list_summary =
 103     MetaspaceAux::chunk_free_list_summary(Metaspace::NonClassType);
 104 
It looks like you pass the wrong MetadataType to chunk_free_list_summary here, 
ClassType and NonClassType should be swapped.

/Mikael

> 
> Thanks,
> Erik
> 
> On 2014-03-06 11:56, Erik Helin wrote:
> > A small bug had found its way into this patch:
> > 
> > metaspace.cpp:
> > +bool MetaspaceAux::has_chunk_free_list(Metaspace::MetadataType mdtype) {
> > +  return Metaspace::get_chunk_manager(mdtype) == NULL;
> > +}
> > 
> > should of course be:
> > 
> > +bool MetaspaceAux::has_chunk_free_list(Metaspace::MetadataType mdtype) {
> > +  return Metaspace::get_chunk_manager(mdtype) != NULL;
> > +}
> > 
> > Please see new webrev at:
> > http://cr.openjdk.java.net/~ehelin/8036703/webrev.01/
> > 
> > Thanks,
> > Erik
> > 
> > On 2014-03-06 10:35, Erik Helin wrote:
> >> Hi all,
> >> 
> >> this patch adds a new trace event -
> >> vm/gc/metaspace/chunk_free_list_summary for getting statistics for
> >> metaspace's chunk free lists. The event contains the numbers of chunks
> >> in the free list and the size of the chunks in the free lists. This
> >> information is provided for all different kinds of chunks - special,
> >> small, medium and humongous.
> >> 
> >> This information will be useful when diagnosing fragmentation issues in
> >> metaspace.
> >> 
> >> Webrev:
> >> http://cr.openjdk.java.net/~ehelin/8036703/webrev.00/
> >> 
> >> Enhancement:
> >> https://bugs.openjdk.java.net/browse/JDK-8036703
> >> 
> >> Testing:
> >> - JFR JTREG tests
> >> - JPRT
> >> - Manually verifying that the numbers look correct by looking at
> >> 
> >>    recordings from small test cases.
> >> 
> >> Thanks,
> >> Erik