From 749cb85e74af448ff14ca23c033f808f9a4b5b54 Mon Sep 17 00:00:00 2001
From: johnc <unknown>
Date: Thu, 20 Sep 2012 09:52:56 -0700
Subject: [PATCH] 7190666: G1: assert(_unused == 0) failed: Inconsistency in
 PLAB stats Summary: Reset the fields in ParGCAllocBuffer, that are used for
 accumulating values for the ResizePLAB sensors in PLABStats, to zero after
 flushing the values to the PLABStats fields. Flush PLABStats values only when
 retiring the final allocation buffers prior to disposing of a
 G1ParScanThreadState object, rather than when retiring every allocation
 buffer. Reviewed-by: jwilhelm, jmasa, ysr

---
 .../vm/gc_implementation/g1/g1CollectedHeap.hpp  |  4 +---
 .../shared/parGCAllocBuffer.cpp                  |  9 ++++++++-
 .../shared/parGCAllocBuffer.hpp                  | 16 +++++++++++++++-
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
index 9eedf804a..1a9a02896 100644
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
@@ -1851,9 +1851,7 @@ public:
     if (word_sz * 100 < gclab_word_size * ParallelGCBufferWastePct) {
       G1ParGCAllocBuffer* alloc_buf = alloc_buffer(purpose);
       add_to_alloc_buffer_waste(alloc_buf->words_remaining());
-      alloc_buf->flush_stats_and_retire(_g1h->stats_for_purpose(purpose),
-                                        false /* end_of_gc */,
-                                        false /* retain */);
+      alloc_buf->retire(false /* end_of_gc */, false /* retain */);
 
       HeapWord* buf = _g1h->par_allocate_during_gc(purpose, gclab_word_size);
       if (buf == NULL) return NULL; // Let caller handle allocation failure.
diff --git a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp
index b768df970..d159dbe28 100644
--- a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp
+++ b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.cpp
@@ -90,7 +90,14 @@ void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
 void PLABStats::adjust_desired_plab_sz() {
   assert(ResizePLAB, "Not set");
   if (_allocated == 0) {
-    assert(_unused == 0, "Inconsistency in PLAB stats");
+    assert(_unused == 0,
+           err_msg("Inconsistency in PLAB stats: "
+                   "_allocated: "SIZE_FORMAT", "
+                   "_wasted: "SIZE_FORMAT", "
+                   "_unused: "SIZE_FORMAT", "
+                   "_used  : "SIZE_FORMAT,
+                   _allocated, _wasted, _unused, _used));
+
     _allocated = 1;
   }
   double wasted_frac    = (double)_unused/(double)_allocated;
diff --git a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp
index fcb4c786f..cb35ee28f 100644
--- a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp
+++ b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp
@@ -52,6 +52,10 @@ protected:
   static size_t FillerHeaderSize;
   static size_t AlignmentReserve;
 
+  // Flush the stats supporting ergonomic sizing of PLAB's
+  // Should not be called directly
+  void flush_stats(PLABStats* stats);
+
 public:
   // Initializes the buffer to be empty, but with the given "word_sz".
   // Must get initialized with "set_buf" for an allocation to succeed.
@@ -120,12 +124,22 @@ public:
   }
 
   // Flush the stats supporting ergonomic sizing of PLAB's
-  void flush_stats(PLABStats* stats);
+  // and retire the current buffer.
   void flush_stats_and_retire(PLABStats* stats, bool end_of_gc, bool retain) {
     // We flush the stats first in order to get a reading of
     // unused space in the last buffer.
     if (ResizePLAB) {
       flush_stats(stats);
+
+      // Since we have flushed the stats we need to clear
+      // the _allocated and _wasted fields. Not doing so
+      // will artifically inflate the values in the stats
+      // to which we add them.
+      // The next time we flush these values, we will add
+      // what we have just flushed in addition to the size
+      // of the buffers allocated between now and then.
+      _allocated = 0;
+      _wasted = 0;
     }
     // Retire the last allocation buffer.
     retire(end_of_gc, retain);
-- 
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