Landing for Anton Muhin's tcmalloc patch:

http://codereview.chromium.org/180021/show

Restore decommitting in IncrementalScavenge and draft Scavenge method to
be invoked periodically
to reduce amount of committed pages.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/187008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25188 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 128 insertions, 14 deletions

diff --git a/third_party/tcmalloc/page_heap.cc b/third_party/tcmalloc/page_heap.cc
index afe9e34..7e54bf5 100644
--- a/third_party/tcmalloc/page_heap.cc
+++ b/third_party/tcmalloc/page_heap.cc
@@ -51,7 +51,12 @@ PageHeap::PageHeap()
       pagemap_cache_(0),
       free_pages_(0),
       system_bytes_(0),
+#if DEFER_DECOMMIT
+      free_committed_pages_(0),
+      pages_committed_since_last_scavenge_(0),
+#else
       scavenge_counter_(0),
+#endif
       // Start scavenging at kMaxPages list
       scavenge_index_(kMaxPages-1) {
   COMPILE_ASSERT(kNumClasses <= (1 << PageMapCache::kValuebits), valuebits);
@@ -150,6 +155,16 @@ Span* PageHeap::Split(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)
+  );
+#if DEFER_DECOMMIT
+  pages_committed_since_last_scavenge_ += span->length;
+#endif
+}
+
 Span* PageHeap::Carve(Span* span, Length n) {
   ASSERT(n > 0);
   ASSERT(span->location != Span::IN_USE);
@@ -175,14 +190,21 @@ Span* PageHeap::Carve(Span* span, Length n) {
     span->length = n;
     pagemap_.set(span->start + n - 1, span);
   }
-  ASSERT(Check());
-  free_pages_ -= n;
   if (old_location == Span::ON_RETURNED_FREELIST) {
     // We need to recommit this address space.
-    TCMalloc_SystemCommit(
-        reinterpret_cast<void*>(span->start << kPageShift),
-        static_cast<size_t>(span->length << kPageShift));
+    CommitSpan(span);
+  } else {
+#if DEFER_DECOMMIT
+    // The newly allocated memory is from a span that's already committed.
+    // Update the free_committed_pages_ count.
+    ASSERT(free_committed_pages_ >= n);
+    free_committed_pages_ -= n;
+#endif
   }
+  ASSERT(span->location == Span::IN_USE);
+  ASSERT(span->length == n);
+  ASSERT(Check());
+  free_pages_ -= n;
   return span;
 }
 
@@ -201,10 +223,9 @@ void PageHeap::Delete(Span* span) {
   // care about the pagemap entries for the boundaries.
   //
   // Note that the spans we merge into "span" may come out of
-  // a "normal" list.  For simplicity, we move these into the
-  // "returned" list of the appropriate size class.  We do this
-  // so that we can maximize large, continuous blocks of freed
-  // space.
+  // a "returned" list.  We move those into "normal" list
+  // as for 'immediate' operations we favour committing over
+  // decommitting (decommitting is performed offline).
   const PageID p = span->start;
   const Length n = span->length;
   Span* prev = GetDescriptor(p-1);
@@ -212,6 +233,12 @@ void PageHeap::Delete(Span* span) {
     // Merge preceding span into this span
     ASSERT(prev->start + prev->length == p);
     const Length len = prev->length;
+    if (prev->location == Span::ON_RETURNED_FREELIST) {
+      CommitSpan(prev);
+#if DEFER_DECOMMIT
+      free_committed_pages_ += len;
+#endif
+    }
     DLL_Remove(prev);
     DeleteSpan(prev);
     span->start -= len;
@@ -224,6 +251,12 @@ void PageHeap::Delete(Span* span) {
     // Merge next span into this span
     ASSERT(next->start == p+n);
     const Length len = next->length;
+    if (next->location == Span::ON_RETURNED_FREELIST) {
+      CommitSpan(next);
+#if DEFER_DECOMMIT
+      free_committed_pages_ += len;
+#endif
+    }
     DLL_Remove(next);
     DeleteSpan(next);
     span->length += len;
@@ -232,19 +265,93 @@ void PageHeap::Delete(Span* span) {
   }
 
   Event(span, 'D', span->length);
-  span->location = Span::ON_RETURNED_FREELIST;
-  TCMalloc_SystemRelease(reinterpret_cast<void*>(span->start << kPageShift),
-                         static_cast<size_t>(span->length << kPageShift));
+  span->location = Span::ON_NORMAL_FREELIST;
   if (span->length < kMaxPages)
-    DLL_Prepend(&free_[span->length].returned, span);
+    DLL_Prepend(&free_[span->length].normal, span);
   else
-    DLL_Prepend(&large_.returned, span);
+    DLL_Prepend(&large_.normal, span);
   free_pages_ += n;
+#if DEFER_DECOMMIT
+  free_committed_pages_ += n;
+#endif
 
+#if DEFER_DECOMMIT
+  // TODO(antonm): notify that could start scavenging
+#else
   IncrementalScavenge(n);
+#endif
   ASSERT(Check());
 }
 
+
+void PageHeap::Scavenge() {
+#if DEFER_DECOMMIT
+  // If we have to commit memory since the last scavenge, it means we don't
+  // have enough free committed pages of necessary size for the amount of
+  // allocations that we do.  So hold off on releasing memory back to the system.
+  if (pages_committed_since_last_scavenge_ > 0) {
+    pages_committed_since_last_scavenge_ = 0;
+    return;
+  }
+
+  if (free_committed_pages_ <= kMinimumFreeCommittedPageCount) {
+    return;
+  }
+
+  uint64_t to_decommit = std::min(
+      free_committed_pages_ - kMinimumFreeCommittedPageCount,
+      free_committed_pages_ / kMaxScavengeAmountFactor);
+  to_decommit = DecommitFromSpanList(&large_, to_decommit);
+  for (int i = kMaxPages - 1; i >= 0; i--) {
+    to_decommit = DecommitFromSpanList(&free_[i], to_decommit);
+  }
+
+  // Force at least one decommit from large list, otherwise big sized blocks
+  // sitting might block as from releasing smaller blocks behind.
+  if (to_decommit > 0) {
+    if (!DLL_IsEmpty(&large_.normal)) {
+      DecommitLastSpan(&large_, large_.normal.prev);
+    }
+  }
+#endif
+}
+
+#if DEFER_DECOMMIT
+Length PageHeap::DecommitLastSpan(SpanList* span_list, Span* span) {
+  ASSERT(!DLL_IsEmpty(&span_list->normal));
+  ASSERT(span_list->normal.prev == span);
+
+  Length length = span->length;
+
+  DLL_Remove(span);
+
+  TCMalloc_SystemRelease(reinterpret_cast<void*>(span->start << kPageShift), span->length << kPageShift);
+  span->location = Span::ON_RETURNED_FREELIST;
+  ASSERT(free_committed_pages_ >= length);
+  free_committed_pages_ -= length;
+
+  DLL_Prepend(&span_list->returned, span);
+
+  return length;
+}
+
+uint64_t PageHeap::DecommitFromSpanList(SpanList* span_list, uint64_t to_decommit) {
+  while (!DLL_IsEmpty(&span_list->normal)) {
+    // Release the last span on the normal portion of this list.
+    Span* span = span_list->normal.prev;
+
+    if (span->length > to_decommit) {
+      return to_decommit;
+    }
+
+    to_decommit -= DecommitLastSpan(span_list, span);
+  }
+
+  return to_decommit;
+}
+
+#else
+
 void PageHeap::IncrementalScavenge(Length n) {
   // Fast path; not yet time to release memory
   scavenge_counter_ -= n;
@@ -304,6 +411,7 @@ void PageHeap::IncrementalScavenge(Length n) {
   // Nothing to scavenge, delay for a while
   scavenge_counter_ = kDefaultReleaseDelay;
 }
+#endif
 
 void PageHeap::RegisterSizeClass(Span* span, size_t sc) {
   // Associate span object with all interior pages as well
@@ -405,6 +513,9 @@ bool PageHeap::GrowHeap(Length n) {
     if (ptr == NULL) return false;
   }
   ask = actual_size >> kPageShift;
+#if DEFER_DECOMMIT
+  pages_committed_since_last_scavenge_ += ask;
+#endif
   RecordGrowth(ask << kPageShift);
 
   uint64_t old_system_bytes = system_bytes_;
@@ -490,6 +601,9 @@ void PageHeap::ReleaseFreePages() {
   }
   ReleaseFreeList(&large_.normal, &large_.returned);
   ASSERT(Check());
+#if DEFER_DECOMMIT
+  free_committed_pages_ = 0;
+#endif
 }
 
 }  // namespace tcmalloc