8277383: VM.metaspace optionally show chunk freelist details

src/hotspot/share/memory/metaspace/metaspaceDCmd.cpp

@@ -42,6 +42,7 @@ MetaspaceDCmd::MetaspaceDCmd(outputStream* output, bool heap) :
   _by_spacetype("by-spacetype", "Break down numbers by loader type.", "BOOLEAN", false, "false"),
   _by_chunktype("by-chunktype", "Break down numbers by chunk type.", "BOOLEAN", false, "false"),
   _show_vslist("vslist", "Shows details about the underlying virtual space.", "BOOLEAN", false, "false"),
+  _show_chunkfreelist("chunkfreelist", "Shows details about global chunk free lists (ChunkManager).", "BOOLEAN", false, "false"),
   _scale("scale", "Memory usage in which to scale. Valid values are: 1, KB, MB or GB (fixed scale) "
          "or \"dynamic\" for a dynamically choosen scale.",
          "STRING", false, "dynamic"),
@@ -53,6 +54,7 @@ MetaspaceDCmd::MetaspaceDCmd(outputStream* output, bool heap) :
   _dcmdparser.add_dcmd_option(&_by_chunktype);
   _dcmdparser.add_dcmd_option(&_by_spacetype);
   _dcmdparser.add_dcmd_option(&_show_vslist);
+  _dcmdparser.add_dcmd_option(&_show_chunkfreelist);
   _dcmdparser.add_dcmd_option(&_scale);
 }
 
@@ -96,6 +98,7 @@ void MetaspaceDCmd::execute(DCmdSource source, TRAPS) {
     if (_by_chunktype.value())         flags |= (int)MetaspaceReporter::Option::BreakDownByChunkType;
     if (_by_spacetype.value())         flags |= (int)MetaspaceReporter::Option::BreakDownBySpaceType;
     if (_show_vslist.value())          flags |= (int)MetaspaceReporter::Option::ShowVSList;
+    if (_show_chunkfreelist.value())   flags |= (int)MetaspaceReporter::Option::ShowChunkFreeList;
     VM_PrintMetadata op(output(), scale, flags);
     VMThread::execute(&op);
   }

src/hotspot/share/memory/metaspace/metaspaceDCmd.hpp

@@ -38,6 +38,7 @@ class MetaspaceDCmd : public DCmdWithParser {
   DCmdArgument<bool> _by_spacetype;
   DCmdArgument<bool> _by_chunktype;
   DCmdArgument<bool> _show_vslist;
+  DCmdArgument<bool> _show_chunkfreelist;
   DCmdArgument<char*> _scale;
   DCmdArgument<bool> _show_classes;
 public:

src/hotspot/share/memory/metaspace/metaspaceReporter.cpp

@@ -300,6 +300,24 @@ void MetaspaceReporter::print_report(outputStream* out, size_t scale, int flags)
     out->cr();
   }
 
+  // -- Print Chunkmanager details.
+  if ((flags & (int)Option::ShowChunkFreeList) > 0) {
+    out->cr();
+    out->print_cr("Chunk freelist details:");
+    if (Metaspace::using_class_space()) {
+      out->print_cr("   Non-Class:");
+    }
+    ChunkManager::chunkmanager_nonclass()->print_on(out);
+    out->cr();
+    if (Metaspace::using_class_space()) {
+      out->print_cr("       Class:");
+      ChunkManager::chunkmanager_class()->print_on(out);
+      out->cr();
+    }
+  }
+  out->cr();
+
+
   //////////// Waste section ///////////////////////////
   // As a convenience, print a summary of common waste.
   out->cr();

src/hotspot/share/memory/metaspace/metaspaceReporter.hpp

@@ -44,7 +44,9 @@ class MetaspaceReporter : public AllStatic {
     // Print details about the underlying virtual spaces.
     ShowVSList                  = (1 << 3),
     // If show_loaders: show loaded classes for each loader.
-    ShowClasses                 = (1 << 4)
+    ShowClasses                 = (1 << 4),
+    // Print details about the underlying virtual spaces.
+    ShowChunkFreeList           = (1 << 5)
   };
 
   // This will print out a basic metaspace usage report but

test/hotspot/jtreg/runtime/Metaspace/PrintMetaspaceDcmd.java

@@ -168,6 +168,29 @@ private static void doTheCCSPropTest(boolean usesCompressedClassSpace) throws Ex
         output.shouldContain("Virtual space list");
         output.shouldMatch("node.*reserved.*committed.*used.*");
 
+        pb.command(new String[] { JDKToolFinder.getJDKTool("jcmd"), pid, "VM.metaspace", "chunkfreelist"});
+        // Output should look somewhat like this...
+        // vvvvvvvvvvvvvvvv
+        // Chunk freelist details:
+        // Non-Class:
+        // cm non-class-space: 5 chunks, total word size: 402944.
+        //         -- List[lv00]: empty
+        //         -- List[lv01]:  - <Chunk @0x00007f925c124090, state f, base 0x00007f9208600000, level lv01 (262144 words), used 0 words, committed 0 words.> - total : 1 chunks.
+        //         -- List[lv02]:  - <Chunk @0x00007f925c1240d8, state f, base 0x00007f9208500000, level lv02 (131072 words), used 0 words, committed 0 words.> - total : 1 chunks.
+        //         -- List[lv03]: empty
+        // .....
+        //
+        // total chunks: 5, total word size: 402944.
+        // ^^^^^^^^^^^^^^^^^
+        // .... but the actual number of chunks in the freelist is difficult to predict and may be low or zero since
+        //  no class unloading happened yet.
+        output = new OutputAnalyzer(pb.start());
+        output.shouldHaveExitValue(0);
+        output.shouldContain("Chunk freelist details:");
+        // ... but we should see at least one one chunk somewhere, the list should never be empty.
+        output.shouldMatch(".*-- List\\[lv00\\].*");
+        output.shouldMatch(".*total chunks.*total word size.*");
+
         // Test with different scales
         pb.command(new String[] { JDKToolFinder.getJDKTool("jcmd"), pid, "VM.metaspace", "scale=G"});
         output = new OutputAnalyzer(pb.start());