[NOT TO COMMIT!] r109: Diff of the current tcmalloc from the original google-perftools r109.

third_party/tcmalloc/chromium/src/page_heap.cc

 // Copyright (c) 2008, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 82 matching lines @@
 Span* PageHeap::New(Length n) {
   ASSERT(Check());
   ASSERT(n > 0);
 
   Span* result = SearchFreeAndLargeLists(n);
   if (result != NULL)
     return result;
 
   // Grow the heap and try again.
   if (!GrowHeap(n)) {
+    ASSERT(stats_.unmapped_bytes+ stats_.committed_bytes==stats_.system_bytes);
     ASSERT(Check());
     return NULL;
   }
   return SearchFreeAndLargeLists(n);
 }
 
 Span* PageHeap::AllocLarge(Length n) {
   // find the best span (closest to n in size).
   // The following loops implements address-ordered best-fit.
   Span *best = NULL;
@@ skipping 40 matching lines @@
   Span* leftover = NewSpan(span->start + n, extra);
   ASSERT(leftover->location == Span::IN_USE);
   Event(leftover, 'U', extra);
   RecordSpan(leftover);
   pagemap_.set(span->start + n - 1, span); // Update map from pageid to span
   span->length = n;
 
   return leftover;
 }
 
+void PageHeap::CommitSpan(Span* span) {
+  TCMalloc_SystemCommit(reinterpret_cast<void*>(span->start << kPageShift),
+                        static_cast<size_t>(span->length << kPageShift));
+  stats_.committed_bytes += span->length << kPageShift;
+}
+
+void PageHeap::DecommitSpan(Span* span) {
+  TCMalloc_SystemRelease(reinterpret_cast<void*>(span->start << kPageShift),
+                         static_cast<size_t>(span->length << kPageShift));
+  stats_.committed_bytes -= span->length << kPageShift;
+}
+
 Span* PageHeap::Carve(Span* span, Length n) {
   ASSERT(n > 0);
   ASSERT(span->location != Span::IN_USE);
   const int old_location = span->location;
   RemoveFromFreeList(span);
   span->location = Span::IN_USE;
   Event(span, 'A', n);
 
   const int extra = span->length - n;
   ASSERT(extra >= 0);
   if (extra > 0) {
     Span* leftover = NewSpan(span->start + n, extra);
     leftover->location = old_location;
     Event(leftover, 'S', extra);
     RecordSpan(leftover);
+
+    // The previous span of |leftover| was just splitted -- no need to
+    // coalesce them. The next span of |leftover| was not previously coalesced
+    // with |span|, i.e. is NULL or has got location other than |old_location|.
+    const PageID p = leftover->start;
+    const Length len = leftover->length;
+    Span* next = GetDescriptor(p+len);
+    ASSERT (next == NULL ||
+            next->location == Span::IN_USE ||
+            next->location != leftover->location);
+
     PrependToFreeList(leftover);  // Skip coalescing - no candidates possible
     span->length = n;
     pagemap_.set(span->start + n - 1, span);
   }
   ASSERT(Check());
+  if (old_location == Span::ON_RETURNED_FREELIST) {
+    // We need to recommit this address space.
+    CommitSpan(span);
+  }
+  ASSERT(span->location == Span::IN_USE);
+  ASSERT(span->length == n);
+  ASSERT(stats_.unmapped_bytes+ stats_.committed_bytes==stats_.system_bytes);
   return span;
 }
 
 void PageHeap::Delete(Span* span) {
   ASSERT(Check());
   ASSERT(span->location == Span::IN_USE);
   ASSERT(span->length > 0);
   ASSERT(GetDescriptor(span->start) == span);
   ASSERT(GetDescriptor(span->start + span->length - 1) == span);
   const Length n = span->length;
   span->sizeclass = 0;
   span->sample = 0;
   span->location = Span::ON_NORMAL_FREELIST;
   Event(span, 'D', span->length);
   MergeIntoFreeList(span);  // Coalesces if possible
   IncrementalScavenge(n);
+  ASSERT(stats_.unmapped_bytes+ stats_.committed_bytes==stats_.system_bytes);
   ASSERT(Check());
 }
 
 void PageHeap::MergeIntoFreeList(Span* span) {
   ASSERT(span->location != Span::IN_USE);
 
   // Coalesce -- we guarantee that "p" != 0, so no bounds checking
   // necessary.  We do not bother resetting the stale pagemap
   // entries for the pieces we are merging together because we only
   // care about the pagemap entries for the boundaries.
   //
-  // Note that only similar spans are merged together.  For example,
-  // we do not coalesce "returned" spans with "normal" spans.
+  // Note that the adjacent spans we merge into "span" may come out of a
+  // "normal" (committed) list, and cleanly merge with our IN_USE span, which
+  // is implicitly committed.  If the adjacents spans are on the "returned"
+  // (decommitted) list, then we must get both spans into the same state before
+  // or after we coalesce them.  The current code always decomits. This is
+  // achieved by blindly decommitting the entire coalesced region, which  may
+  // include any combination of committed and decommitted spans, at the end of
+  // the method.
+
+  // TODO(jar): "Always decommit" causes some extra calls to commit when we are
+  // called in GrowHeap() during an allocation :-/.  We need to eval the cost of
+  // that oscillation, and possibly do something to reduce it.
+
+  // TODO(jar): We need a better strategy for deciding to commit, or decommit,
+  // based on memory usage and free heap sizes.
+
   const PageID p = span->start;
   const Length n = span->length;
   Span* prev = GetDescriptor(p-1);
-  if (prev != NULL && prev->location == span->location) {
+  if (prev != NULL && prev->location != Span::IN_USE) {
     // Merge preceding span into this span
     ASSERT(prev->start + prev->length == p);
     const Length len = prev->length;
+    if (prev->location == Span::ON_RETURNED_FREELIST) {
+      // We're about to put the merge span into the returned freelist and call
+      // DecommitSpan() on it, which will mark the entire span including this
+      // one as released and decrease stats_.committed_bytes by the size of the
+      // merged span.  To make the math work out we temporarily increase the
+      // stats_.committed_bytes amount.
+      stats_.committed_bytes += prev->length << kPageShift;
+    }
     RemoveFromFreeList(prev);
     DeleteSpan(prev);
     span->start -= len;
     span->length += len;
     pagemap_.set(span->start, span);
     Event(span, 'L', len);
   }
   Span* next = GetDescriptor(p+n);
-  if (next != NULL && next->location == span->location) {
+  if (next != NULL && next->location != Span::IN_USE) {
     // Merge next span into this span
     ASSERT(next->start == p+n);
     const Length len = next->length;
+    if (next->location == Span::ON_RETURNED_FREELIST) {
+      // See the comment below 'if (prev->location ...' for explanation.
+      stats_.committed_bytes += next->length << kPageShift;
+    }
     RemoveFromFreeList(next);
     DeleteSpan(next);
     span->length += len;
     pagemap_.set(span->start + span->length - 1, span);
     Event(span, 'R', len);
   }
 
+  Event(span, 'D', span->length);
+  span->location = Span::ON_RETURNED_FREELIST;
+  DecommitSpan(span);
   PrependToFreeList(span);
 }
 
 void PageHeap::PrependToFreeList(Span* span) {
   ASSERT(span->location != Span::IN_USE);
   SpanList* list = (span->length < kMaxPages) ? &free_[span->length] : &large_;
   if (span->location == Span::ON_NORMAL_FREELIST) {
     stats_.free_bytes += (span->length << kPageShift);
     DLL_Prepend(&list->normal, span);
   } else {
@@ skipping 244 matching lines @@
       ask = n;
       ptr = TCMalloc_SystemAlloc(ask << kPageShift, &actual_size, kPageSize);
     }
     if (ptr == NULL) return false;
   }
   ask = actual_size >> kPageShift;
   RecordGrowth(ask << kPageShift);
 
   uint64_t old_system_bytes = stats_.system_bytes;
   stats_.system_bytes += (ask << kPageShift);
+  stats_.committed_bytes += (ask << kPageShift);
   const PageID p = reinterpret_cast<uintptr_t>(ptr) >> kPageShift;
   ASSERT(p > 0);
 
   // If we have already a lot of pages allocated, just pre allocate a bunch of
   // memory for the page map. This prevents fragmentation by pagemap metadata
   // when a program keeps allocating and freeing large blocks.
 
   if (old_system_bytes < kPageMapBigAllocationThreshold
       && stats_.system_bytes >= kPageMapBigAllocationThreshold) {
     pagemap_.PreallocateMoreMemory();
   }
 
   // Make sure pagemap_ has entries for all of the new pages.
   // Plus ensure one before and one after so coalescing code
   // does not need bounds-checking.
   if (pagemap_.Ensure(p-1, ask+2)) {
     // Pretend the new area is allocated and then Delete() it to cause
     // any necessary coalescing to occur.
     Span* span = NewSpan(p, ask);
     RecordSpan(span);
     Delete(span);
+    ASSERT(stats_.unmapped_bytes+ stats_.committed_bytes==stats_.system_bytes);
     ASSERT(Check());
     return true;
   } else {
     // We could not allocate memory within "pagemap_"
     // TODO: Once we can return memory to the system, return the new span
     return false;
   }
 }
 
 bool PageHeap::Check() {
@@ skipping 19 matching lines @@
     CHECK_CONDITION(s->location == freelist);  // NORMAL or RETURNED
     CHECK_CONDITION(s->length >= min_pages);
     CHECK_CONDITION(s->length <= max_pages);
     CHECK_CONDITION(GetDescriptor(s->start) == s);
     CHECK_CONDITION(GetDescriptor(s->start+s->length-1) == s);
   }
   return true;
 }
 
 }  // namespace tcmalloc