changeset 14687:480b0109db65

8029799: vm/mlvm/anonloader/stress/oome prints warning: CodeHeap: # of free blocks > 10000 Summary: Double CodeCacheSegmentSize from 64 byte to 128 bytes if tiered compilation is enabled Reviewed-by: kvn, twisti
author anoll
date Fri, 07 Mar 2014 07:42:40 +0100
parents 97586c131ac8
children 5e2306b00977
files src/share/vm/code/codeCache.cpp src/share/vm/code/codeCache.hpp src/share/vm/memory/heap.cpp src/share/vm/memory/heap.hpp src/share/vm/runtime/arguments.cpp src/share/vm/runtime/globals.hpp
diffstat 6 files changed, 207 insertions(+), 174 deletions(-) [+]
line wrap: on
line diff
--- a/src/share/vm/code/codeCache.cpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/code/codeCache.cpp	Fri Mar 07 07:42:40 2014 +0100
@@ -198,14 +198,12 @@
   }
   maxCodeCacheUsed = MAX2(maxCodeCacheUsed, ((address)_heap->high_boundary() -
                           (address)_heap->low_boundary()) - unallocated_capacity());
-  verify_if_often();
   print_trace("allocation", cb, size);
   return cb;
 }
 
 void CodeCache::free(CodeBlob* cb) {
   assert_locked_or_safepoint(CodeCache_lock);
-  verify_if_often();
 
   print_trace("free", cb);
   if (cb->is_nmethod()) {
@@ -221,7 +219,6 @@
 
   _heap->deallocate(cb);
 
-  verify_if_often();
   assert(_number_of_blobs >= 0, "sanity check");
 }
 
@@ -244,12 +241,6 @@
 }
 
 
-void CodeCache::flush() {
-  assert_locked_or_safepoint(CodeCache_lock);
-  Unimplemented();
-}
-
-
 // Iteration over CodeBlobs
 
 #define FOR_ALL_BLOBS(var)       for (CodeBlob *var =       first() ; var != NULL; var =       next(var) )
@@ -269,7 +260,7 @@
 CodeBlob* CodeCache::find_blob(void* start) {
   CodeBlob* result = find_blob_unsafe(start);
   if (result == NULL) return NULL;
-  // We could potientially look up non_entrant methods
+  // We could potentially look up non_entrant methods
   guarantee(!result->is_zombie() || result->is_locked_by_vm() || is_error_reported(), "unsafe access to zombie method");
   return result;
 }
@@ -741,17 +732,26 @@
   }
 }
 
+void CodeCache::print_memory_overhead() {
+  size_t wasted_bytes = 0;
+  CodeBlob *cb;
+  for (cb = first(); cb != NULL; cb = next(cb)) {
+    HeapBlock* heap_block = ((HeapBlock*)cb) - 1;
+    wasted_bytes += heap_block->length() * CodeCacheSegmentSize - cb->size();
+  }
+  // Print bytes that are allocated in the freelist
+  ttyLocker ttl;
+  tty->print_cr("Number of elements in freelist: %d",    freelist_length());
+  tty->print_cr("Allocated in freelist:          %dkB",  bytes_allocated_in_freelist()/K);
+  tty->print_cr("Unused bytes in CodeBlobs:      %dkB",  (int)(wasted_bytes/K));
+  tty->print_cr("Segment map size:               %dkB",  allocated_segments()/K); // 1 byte per segment
+}
+
 //------------------------------------------------------------------------------------------------
 // Non-product version
 
 #ifndef PRODUCT
 
-void CodeCache::verify_if_often() {
-  if (VerifyCodeCacheOften) {
-    _heap->verify();
-  }
-}
-
 void CodeCache::print_trace(const char* event, CodeBlob* cb, int size) {
   if (PrintCodeCache2) {  // Need to add a new flag
     ResourceMark rm;
@@ -774,7 +774,7 @@
   int nmethodUnloaded = 0;
   int nmethodJava = 0;
   int nmethodNative = 0;
-  int maxCodeSize = 0;
+  int max_nm_size = 0;
   ResourceMark rm;
 
   CodeBlob *cb;
@@ -798,13 +798,11 @@
       if(nm->is_not_entrant()) { nmethodNotEntrant++; }
       if(nm->is_zombie()) { nmethodZombie++; }
       if(nm->is_unloaded()) { nmethodUnloaded++; }
-      if(nm->is_native_method()) { nmethodNative++; }
+      if(nm->method() != NULL && nm->is_native_method()) { nmethodNative++; }
 
       if(nm->method() != NULL && nm->is_java_method()) {
         nmethodJava++;
-        if (nm->insts_size() > maxCodeSize) {
-          maxCodeSize = nm->insts_size();
-        }
+        max_nm_size = MAX2(max_nm_size, nm->size());
       }
     } else if (cb->is_runtime_stub()) {
       runtimeStubCount++;
@@ -820,18 +818,19 @@
   }
 
   int bucketSize = 512;
-  int bucketLimit = maxCodeSize / bucketSize + 1;
+  int bucketLimit = max_nm_size / bucketSize + 1;
   int *buckets = NEW_C_HEAP_ARRAY(int, bucketLimit, mtCode);
-  memset(buckets,0,sizeof(int) * bucketLimit);
+  memset(buckets, 0, sizeof(int) * bucketLimit);
 
   for (cb = first(); cb != NULL; cb = next(cb)) {
     if (cb->is_nmethod()) {
       nmethod* nm = (nmethod*)cb;
       if(nm->is_java_method()) {
-        buckets[nm->insts_size() / bucketSize]++;
-      }
+        buckets[nm->size() / bucketSize]++;
+       }
     }
   }
+
   tty->print_cr("Code Cache Entries (total of %d)",total);
   tty->print_cr("-------------------------------------------------");
   tty->print_cr("nmethods: %d",nmethodCount);
@@ -858,6 +857,7 @@
   }
 
   FREE_C_HEAP_ARRAY(int, buckets, mtCode);
+  print_memory_overhead();
 }
 
 #endif // !PRODUCT
--- a/src/share/vm/code/codeCache.hpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/code/codeCache.hpp	Fri Mar 07 07:42:40 2014 +0100
@@ -58,12 +58,13 @@
   static bool _needs_cache_clean;
   static nmethod* _scavenge_root_nmethods;  // linked via nm->scavenge_root_link()
 
-  static void verify_if_often() PRODUCT_RETURN;
-
   static void mark_scavenge_root_nmethods() PRODUCT_RETURN;
   static void verify_perm_nmethods(CodeBlobClosure* f_or_null) PRODUCT_RETURN;
 
   static int _codemem_full_count;
+  static size_t bytes_allocated_in_freelist() { return _heap->allocated_in_freelist(); }
+  static int    allocated_segments()          { return _heap->allocated_segments(); }
+  static size_t freelist_length()             { return _heap->freelist_length(); }
 
  public:
 
@@ -78,7 +79,6 @@
   static int alignment_unit();                      // guaranteed alignment of all CodeBlobs
   static int alignment_offset();                    // guaranteed offset of first CodeBlob byte within alignment unit (i.e., allocation header)
   static void free(CodeBlob* cb);                   // frees a CodeBlob
-  static void flush();                              // flushes all CodeBlobs
   static bool contains(void *p);                    // returns whether p is included
   static void blobs_do(void f(CodeBlob* cb));       // iterates over all CodeBlobs
   static void blobs_do(CodeBlobClosure* f);         // iterates over all CodeBlobs
@@ -150,6 +150,7 @@
   // Printing/debugging
   static void print();                           // prints summary
   static void print_internals();
+  static void print_memory_overhead();
   static void verify();                          // verifies the code cache
   static void print_trace(const char* event, CodeBlob* cb, int size = 0) PRODUCT_RETURN;
   static void print_summary(outputStream* st, bool detailed = true); // Prints a summary of the code cache usage
--- a/src/share/vm/memory/heap.cpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/memory/heap.cpp	Fri Mar 07 07:42:40 2014 +0100
@@ -43,6 +43,7 @@
   _next_segment                 = 0;
   _freelist                     = NULL;
   _freelist_segments            = 0;
+  _freelist_length              = 0;
 }
 
 
@@ -53,7 +54,7 @@
   address p = (address)_segmap.low() + beg;
   address q = (address)_segmap.low() + end;
   // initialize interval
-  while (p < q) *p++ = 0xFF;
+  while (p < q) *p++ = free_sentinel;
 }
 
 
@@ -67,7 +68,7 @@
   int i = 0;
   while (p < q) {
     *p++ = i++;
-    if (i == 0xFF) i = 1;
+    if (i == free_sentinel) i = 1;
   }
 }
 
@@ -139,11 +140,6 @@
 }
 
 
-void CodeHeap::release() {
-  Unimplemented();
-}
-
-
 bool CodeHeap::expand_by(size_t size) {
   // expand _memory space
   size_t dm = align_to_page_size(_memory.committed_size() + size) - _memory.committed_size();
@@ -157,8 +153,8 @@
     assert(_number_of_reserved_segments >= _number_of_committed_segments, "just checking");
     // expand _segmap space
     size_t ds = align_to_page_size(_number_of_committed_segments) - _segmap.committed_size();
-    if (ds > 0) {
-      if (!_segmap.expand_by(ds)) return false;
+    if ((ds > 0) && !_segmap.expand_by(ds)) {
+      return false;
     }
     assert(_segmap.committed_size() >= (size_t) _number_of_committed_segments, "just checking");
     // initialize additional segmap entries
@@ -167,12 +163,6 @@
   return true;
 }
 
-
-void CodeHeap::shrink_by(size_t size) {
-  Unimplemented();
-}
-
-
 void CodeHeap::clear() {
   _next_segment = 0;
   mark_segmap_as_free(0, _number_of_committed_segments);
@@ -180,26 +170,23 @@
 
 
 void* CodeHeap::allocate(size_t instance_size, bool is_critical) {
-  size_t number_of_segments = size_to_segments(instance_size + sizeof(HeapBlock));
+  size_t number_of_segments = size_to_segments(instance_size + header_size());
   assert(segments_to_size(number_of_segments) >= sizeof(FreeBlock), "not enough room for FreeList");
 
   // First check if we can satisfy request from freelist
-  debug_only(verify());
+  NOT_PRODUCT(verify());
   HeapBlock* block = search_freelist(number_of_segments, is_critical);
-  debug_only(if (VerifyCodeCacheOften) verify());
+  NOT_PRODUCT(verify());
+
   if (block != NULL) {
     assert(block->length() >= number_of_segments && block->length() < number_of_segments + CodeCacheMinBlockLength, "sanity check");
     assert(!block->free(), "must be marked free");
-#ifdef ASSERT
-    memset((void *)block->allocated_space(), badCodeHeapNewVal, instance_size);
-#endif
+    DEBUG_ONLY(memset((void*)block->allocated_space(), badCodeHeapNewVal, instance_size));
     return block->allocated_space();
   }
 
   // Ensure minimum size for allocation to the heap.
-  if (number_of_segments < CodeCacheMinBlockLength) {
-    number_of_segments = CodeCacheMinBlockLength;
-  }
+  number_of_segments = MAX2((int)CodeCacheMinBlockLength, (int)number_of_segments);
 
   if (!is_critical) {
     // Make sure the allocation fits in the unallocated heap without using
@@ -215,9 +202,7 @@
     HeapBlock* b =  block_at(_next_segment);
     b->initialize(number_of_segments);
     _next_segment += number_of_segments;
-#ifdef ASSERT
-    memset((void *)b->allocated_space(), badCodeHeapNewVal, instance_size);
-#endif
+    DEBUG_ONLY(memset((void *)b->allocated_space(), badCodeHeapNewVal, instance_size));
     return b->allocated_space();
   } else {
     return NULL;
@@ -230,28 +215,56 @@
   // Find start of HeapBlock
   HeapBlock* b = (((HeapBlock *)p) - 1);
   assert(b->allocated_space() == p, "sanity check");
-#ifdef ASSERT
-  memset((void *)b->allocated_space(),
-         badCodeHeapFreeVal,
-         segments_to_size(b->length()) - sizeof(HeapBlock));
-#endif
+  DEBUG_ONLY(memset((void *)b->allocated_space(), badCodeHeapFreeVal,
+             segments_to_size(b->length()) - sizeof(HeapBlock)));
   add_to_freelist(b);
-
-  debug_only(if (VerifyCodeCacheOften) verify());
+  NOT_PRODUCT(verify());
 }
 
-
+/**
+ * Uses segment map to find the the start (header) of a nmethod. This works as follows:
+ * The memory of the code cache is divided into 'segments'. The size of a segment is
+ * determined by -XX:CodeCacheSegmentSize=XX. Allocation in the code cache can only
+ * happen at segment boundaries. A pointer in the code cache can be mapped to a segment
+ * by calling segment_for(addr). Each time memory is requested from the code cache,
+ * the segmap is updated accordingly. See the following example, which illustrates the
+ * state of code cache and the segment map: (seg -> segment, nm ->nmethod)
+ *
+ *          code cache          segmap
+ *         -----------        ---------
+ * seg 1   | nm 1    |   ->   | 0     |
+ * seg 2   | nm 1    |   ->   | 1     |
+ * ...     | nm 1    |   ->   | ..    |
+ * seg m   | nm 2    |   ->   | 0     |
+ * seg m+1 | nm 2    |   ->   | 1     |
+ * ...     | nm 2    |   ->   | 2     |
+ * ...     | nm 2    |   ->   | ..    |
+ * ...     | nm 2    |   ->   | 0xFE  |
+ * seg m+n | nm 2    |   ->   | 1     |
+ * ...     | nm 2    |   ->   |       |
+ *
+ * A value of '0' in the segmap indicates that this segment contains the beginning of
+ * an nmethod. Let's walk through a simple example: If we want to find the start of
+ * an nmethod that falls into seg 2, we read the value of the segmap[2]. The value
+ * is an offset that points to the segment that contains the start of the nmethod.
+ * Another example: If we want to get the start of nm 2, and we happen to get a pointer
+ * that points to seg m+n, we first read seg[n+m], which returns '1'. So we have to
+ * do one more read of the segmap[m+n-1] to finally get the segment header.
+ */
 void* CodeHeap::find_start(void* p) const {
   if (!contains(p)) {
     return NULL;
   }
-  size_t i = segment_for(p);
-  address b = (address)_segmap.low();
-  if (b[i] == 0xFF) {
+  size_t seg_idx = segment_for(p);
+  address seg_map = (address)_segmap.low();
+  if (is_segment_unused(seg_map[seg_idx])) {
     return NULL;
   }
-  while (b[i] > 0) i -= (int)b[i];
-  HeapBlock* h = block_at(i);
+  while (seg_map[seg_idx] > 0) {
+    seg_idx -= (int)seg_map[seg_idx];
+  }
+
+  HeapBlock* h = block_at(seg_idx);
   if (h->free()) {
     return NULL;
   }
@@ -272,7 +285,7 @@
 }
 
 // Finds the next free heapblock. If the current one is free, that it returned
-void* CodeHeap::next_free(HeapBlock *b) const {
+void* CodeHeap::next_free(HeapBlock* b) const {
   // Since free blocks are merged, there is max. on free block
   // between two used ones
   if (b != NULL && b->free()) b = next_block(b);
@@ -287,7 +300,7 @@
   return NULL;
 }
 
-HeapBlock *CodeHeap::block_start(void *q) const {
+HeapBlock* CodeHeap::block_start(void* q) const {
   HeapBlock* b = (HeapBlock*)find_start(q);
   if (b == NULL) return NULL;
   return b - 1;
@@ -312,6 +325,10 @@
   return _memory.reserved_size();
 }
 
+int CodeHeap::allocated_segments() const {
+  return (int)_next_segment;
+}
+
 size_t CodeHeap::allocated_capacity() const {
   // size of used heap - size on freelist
   return segments_to_size(_next_segment - _freelist_segments);
@@ -325,7 +342,7 @@
 
 // Free list management
 
-FreeBlock *CodeHeap::following_block(FreeBlock *b) {
+FreeBlock* CodeHeap::following_block(FreeBlock *b) {
   return (FreeBlock*)(((address)b) + _segment_size * b->length());
 }
 
@@ -343,7 +360,7 @@
 }
 
 // Try to merge this block with the following block
-void CodeHeap::merge_right(FreeBlock *a) {
+bool CodeHeap::merge_right(FreeBlock* a) {
   assert(a->free(), "must be a free block");
   if (following_block(a) == a->link()) {
     assert(a->link() != NULL && a->link()->free(), "must be free too");
@@ -353,13 +370,20 @@
     // Update find_start map
     size_t beg = segment_for(a);
     mark_segmap_as_used(beg, beg + a->length());
+    _freelist_length--;
+    return true;
   }
+  return false;
 }
 
-void CodeHeap::add_to_freelist(HeapBlock *a) {
+
+void CodeHeap::add_to_freelist(HeapBlock* a) {
   FreeBlock* b = (FreeBlock*)a;
+  _freelist_length++;
+
   assert(b != _freelist, "cannot be removed twice");
 
+
   // Mark as free and update free space count
   _freelist_segments += b->length();
   b->set_free();
@@ -371,95 +395,96 @@
     return;
   }
 
-  // Scan for right place to put into list. List
-  // is sorted by increasing addresses
-  FreeBlock* prev = NULL;
-  FreeBlock* cur  = _freelist;
-  while(cur != NULL && cur < b) {
-    assert(prev == NULL || prev < cur, "must be ordered");
-    prev = cur;
-    cur  = cur->link();
-  }
-
-  assert( (prev == NULL && b < _freelist) ||
-          (prev < b && (cur == NULL || b < cur)), "list must be ordered");
-
-  if (prev == NULL) {
+  // Since the freelist is ordered (smaller addresses -> larger addresses) and the
+  // element we want to insert into the freelist has a smaller address than the first
+  // element, we can simply add 'b' as the first element and we are done.
+  if (b < _freelist) {
     // Insert first in list
     b->set_link(_freelist);
     _freelist = b;
     merge_right(_freelist);
-  } else {
-    insert_after(prev, b);
+    return;
   }
+
+  // Scan for right place to put into list. List
+  // is sorted by increasing addresses
+  FreeBlock* prev = _freelist;
+  FreeBlock* cur  = _freelist->link();
+  while(cur != NULL && cur < b) {
+    assert(prev < cur, "Freelist must be ordered");
+    prev = cur;
+    cur  = cur->link();
+  }
+  assert((prev < b) && (cur == NULL || b < cur), "free-list must be ordered");
+  insert_after(prev, b);
 }
 
-// Search freelist for an entry on the list with the best fit
-// Return NULL if no one was found
+/**
+ * Search freelist for an entry on the list with the best fit.
+ * @return NULL, if no one was found
+ */
 FreeBlock* CodeHeap::search_freelist(size_t length, bool is_critical) {
-  FreeBlock *best_block = NULL;
-  FreeBlock *best_prev  = NULL;
-  size_t best_length = 0;
+  FreeBlock* found_block = NULL;
+  FreeBlock* found_prev  = NULL;
+  size_t     found_length = 0;
 
-  // Search for smallest block which is bigger than length
-  FreeBlock *prev = NULL;
-  FreeBlock *cur = _freelist;
+  FreeBlock* prev = NULL;
+  FreeBlock* cur = _freelist;
+  const size_t critical_boundary = (size_t)high_boundary() - CodeCacheMinimumFreeSpace;
+
+  // Search for first block that fits
   while(cur != NULL) {
-    size_t l = cur->length();
-    if (l >= length && (best_block == NULL || best_length > l)) {
+    if (cur->length() >= length) {
+      // Non critical allocations are not allowed to use the last part of the code heap.
+      // Make sure the end of the allocation doesn't cross into the last part of the code heap.
+      if (!is_critical && (((size_t)cur + length) > critical_boundary)) {
+        // The freelist is sorted by address - if one fails, all consecutive will also fail.
+        break;
+      }
+      // Remember block, its previous element, and its length
+      found_block = cur;
+      found_prev  = prev;
+      found_length = found_block->length();
 
-      // Non critical allocations are not allowed to use the last part of the code heap.
-      if (!is_critical) {
-        // Make sure the end of the allocation doesn't cross into the last part of the code heap
-        if (((size_t)cur + length) > ((size_t)high_boundary() - CodeCacheMinimumFreeSpace)) {
-          // the freelist is sorted by address - if one fails, all consecutive will also fail.
-          break;
-        }
-      }
-
-      // Remember best block, its previous element, and its length
-      best_block = cur;
-      best_prev  = prev;
-      best_length = best_block->length();
+      break;
     }
-
     // Next element in list
     prev = cur;
     cur  = cur->link();
   }
 
-  if (best_block == NULL) {
+  if (found_block == NULL) {
     // None found
     return NULL;
   }
 
-  assert((best_prev == NULL && _freelist == best_block ) ||
-         (best_prev != NULL && best_prev->link() == best_block), "sanity check");
-
   // Exact (or at least good enough) fit. Remove from list.
   // Don't leave anything on the freelist smaller than CodeCacheMinBlockLength.
-  if (best_length < length + CodeCacheMinBlockLength) {
-    length = best_length;
-    if (best_prev == NULL) {
-      assert(_freelist == best_block, "sanity check");
+  if (found_length - length < CodeCacheMinBlockLength) {
+    _freelist_length--;
+    length = found_length;
+    if (found_prev == NULL) {
+      assert(_freelist == found_block, "sanity check");
       _freelist = _freelist->link();
     } else {
+      assert((found_prev->link() == found_block), "sanity check");
       // Unmap element
-      best_prev->set_link(best_block->link());
+      found_prev->set_link(found_block->link());
     }
   } else {
     // Truncate block and return a pointer to the following block
-    best_block->set_length(best_length - length);
-    best_block = following_block(best_block);
     // Set used bit and length on new block
-    size_t beg = segment_for(best_block);
+    found_block->set_length(found_length - length);
+    found_block = following_block(found_block);
+
+    size_t beg = segment_for(found_block);
     mark_segmap_as_used(beg, beg + length);
-    best_block->set_length(length);
+    found_block->set_length(length);
   }
 
-  best_block->set_used();
+  found_block->set_used();
   _freelist_segments -= length;
-  return best_block;
+  return found_block;
 }
 
 //----------------------------------------------------------------------------
@@ -471,33 +496,34 @@
   tty->print_cr("The Heap");
 }
 
+void CodeHeap::verify() {
+  if (VerifyCodeCache) {
+    size_t len = 0;
+    int count = 0;
+    for(FreeBlock* b = _freelist; b != NULL; b = b->link()) {
+      len += b->length();
+      count++;
+      // Check if we have merged all free blocks
+      assert(merge_right(b) == false, "Missed merging opportunity");
+    }
+    // Verify that freelist contains the right amount of free space
+    assert(len == _freelist_segments, "wrong freelist");
+
+    for(HeapBlock* h = first_block(); h != NULL; h = next_block(h)) {
+      if (h->free()) count--;
+    }
+    // Verify that the freelist contains the same number of blocks
+    // than free blocks found on the full list.
+    assert(count == 0, "missing free blocks");
+
+    // Verify that the number of free blocks is not out of hand.
+    static int free_block_threshold = 10000;
+    if (count > free_block_threshold) {
+      warning("CodeHeap: # of free blocks > %d", free_block_threshold);
+      // Double the warning limit
+      free_block_threshold *= 2;
+    }
+  }
+}
+
 #endif
-
-void CodeHeap::verify() {
-  // Count the number of blocks on the freelist, and the amount of space
-  // represented.
-  int count = 0;
-  size_t len = 0;
-  for(FreeBlock* b = _freelist; b != NULL; b = b->link()) {
-    len += b->length();
-    count++;
-  }
-
-  // Verify that freelist contains the right amount of free space
-  //  guarantee(len == _freelist_segments, "wrong freelist");
-
-  // Verify that the number of free blocks is not out of hand.
-  static int free_block_threshold = 10000;
-  if (count > free_block_threshold) {
-    warning("CodeHeap: # of free blocks > %d", free_block_threshold);
-    // Double the warning limit
-    free_block_threshold *= 2;
-  }
-
-  // Verify that the freelist contains the same number of free blocks that is
-  // found on the full list.
-  for(HeapBlock *h = first_block(); h != NULL; h = next_block(h)) {
-    if (h->free()) count--;
-  }
-  //  guarantee(count == 0, "missing free blocks");
-}
--- a/src/share/vm/memory/heap.hpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/memory/heap.hpp	Fri Mar 07 07:42:40 2014 +0100
@@ -92,24 +92,28 @@
 
   FreeBlock*   _freelist;
   size_t       _freelist_segments;               // No. of segments in freelist
+  int          _freelist_length;
+
+  enum { free_sentinel = 0xFF };
 
   // Helper functions
   size_t   size_to_segments(size_t size) const { return (size + _segment_size - 1) >> _log2_segment_size; }
   size_t   segments_to_size(size_t number_of_segments) const { return number_of_segments << _log2_segment_size; }
 
   size_t   segment_for(void* p) const            { return ((char*)p - _memory.low()) >> _log2_segment_size; }
+  bool     is_segment_unused(int val) const      { return val == free_sentinel; }
   HeapBlock* block_at(size_t i) const            { return (HeapBlock*)(_memory.low() + (i << _log2_segment_size)); }
 
   void  mark_segmap_as_free(size_t beg, size_t end);
   void  mark_segmap_as_used(size_t beg, size_t end);
 
   // Freelist management helpers
-  FreeBlock* following_block(FreeBlock *b);
+  FreeBlock* following_block(FreeBlock* b);
   void insert_after(FreeBlock* a, FreeBlock* b);
-  void merge_right (FreeBlock* a);
+  bool merge_right (FreeBlock* a);
 
   // Toplevel freelist management
-  void add_to_freelist(HeapBlock *b);
+  void add_to_freelist(HeapBlock* b);
   FreeBlock* search_freelist(size_t length, bool is_critical);
 
   // Iteration helpers
@@ -120,20 +124,18 @@
 
   // to perform additional actions on creation of executable code
   void on_code_mapping(char* base, size_t size);
+  void clear();                                 // clears all heap contents
 
  public:
   CodeHeap();
 
   // Heap extents
   bool  reserve(size_t reserved_size, size_t committed_size, size_t segment_size);
-  void  release();                               // releases all allocated memory
   bool  expand_by(size_t size);                  // expands committed memory by size
-  void  shrink_by(size_t size);                  // shrinks committed memory by size
-  void  clear();                                 // clears all heap contents
 
   // Memory allocation
   void* allocate  (size_t size, bool is_critical);  // allocates a block of size or returns NULL
-  void  deallocate(void* p);                     // deallocates a block
+  void  deallocate(void* p);                        // deallocates a block
 
   // Attributes
   char* low_boundary() const                     { return _memory.low_boundary (); }
@@ -141,12 +143,13 @@
   char* high_boundary() const                    { return _memory.high_boundary(); }
 
   bool  contains(const void* p) const            { return low_boundary() <= p && p < high(); }
-  void* find_start(void* p) const;              // returns the block containing p or NULL
-  size_t alignment_unit() const;                // alignment of any block
-  size_t alignment_offset() const;              // offset of first byte of any block, within the enclosing alignment unit
-  static size_t header_size();                  // returns the header size for each heap block
+  void* find_start(void* p)     const;           // returns the block containing p or NULL
+  size_t alignment_unit()       const;           // alignment of any block
+  size_t alignment_offset()     const;           // offset of first byte of any block, within the enclosing alignment unit
+  static size_t header_size();                   // returns the header size for each heap block
 
-  // Iteration
+  size_t allocated_in_freelist() const           { return _freelist_segments * CodeCacheSegmentSize; }
+  int    freelist_length()       const           { return _freelist_length; } // number of elements in the freelist
 
   // returns the first block or NULL
   void* first() const       { return next_free(first_block()); }
@@ -156,6 +159,7 @@
   // Statistics
   size_t capacity() const;
   size_t max_capacity() const;
+  int    allocated_segments() const;
   size_t allocated_capacity() const;
   size_t unallocated_capacity() const            { return max_capacity() - allocated_capacity(); }
 
@@ -164,7 +168,7 @@
 
 public:
   // Debugging
-  void verify();
+  void verify() PRODUCT_RETURN;
   void print()  PRODUCT_RETURN;
 };
 
--- a/src/share/vm/runtime/arguments.cpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/runtime/arguments.cpp	Fri Mar 07 07:42:40 2014 +0100
@@ -2407,6 +2407,8 @@
 
   status &= verify_interval(NmethodSweepFraction, 1, ReservedCodeCacheSize/K, "NmethodSweepFraction");
   status &= verify_interval(NmethodSweepActivity, 0, 2000, "NmethodSweepActivity");
+  status &= verify_interval(CodeCacheMinBlockLength, 1, 100, "CodeCacheMinBlockLength");
+  status &= verify_interval(CodeCacheSegmentSize, 1, 1024, "CodeCacheSegmentSize");
 
   // TieredCompilation needs at least 2 compiler threads.
   const int num_min_compiler_threads = (TieredCompilation && (TieredStopAtLevel >= CompLevel_full_optimization)) ? 2 : 1;
--- a/src/share/vm/runtime/globals.hpp	Thu Mar 06 14:35:26 2014 +0100
+++ b/src/share/vm/runtime/globals.hpp	Fri Mar 07 07:42:40 2014 +0100
@@ -814,8 +814,8 @@
   product(bool, PrintOopAddress, false,                                     \
           "Always print the location of the oop")                           \
                                                                             \
-  notproduct(bool, VerifyCodeCacheOften, false,                             \
-          "Verify compiled-code cache often")                               \
+  notproduct(bool, VerifyCodeCache, false,                                  \
+          "Verify code cache on memory allocation/deallocation")            \
                                                                             \
   develop(bool, ZapDeadCompiledLocals, false,                               \
           "Zap dead locals in compiler frames")                             \
@@ -3296,8 +3296,8 @@
           "disable this feature")                                           \
                                                                             \
   /* code cache parameters */                                               \
-  /* ppc64 has large code-entry alignment. */                               \
-  develop(uintx, CodeCacheSegmentSize, 64 PPC64_ONLY(+64),                  \
+  /* ppc64/tiered compilation has large code-entry alignment. */            \
+  develop(uintx, CodeCacheSegmentSize, 64 PPC64_ONLY(+64) NOT_PPC64(TIERED_ONLY(+64)),\
           "Code cache segment size (in bytes) - smallest unit of "          \
           "allocation")                                                     \
                                                                             \