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

third_party/tcmalloc/chromium/src/pagemap.h

Index: third_party/tcmalloc/chromium/src/pagemap.h
diff --git a/third_party/tcmalloc/chromium/src/pagemap.h b/third_party/tcmalloc/chromium/src/pagemap.h
index 27cb3da050f23c46f3a058fefe66079fab41071b..0db01c4bc8bca5d2224446693e78515e4475ff00 100644
--- a/third_party/tcmalloc/chromium/src/pagemap.h
+++ b/third_party/tcmalloc/chromium/src/pagemap.h
@@ -56,6 +56,12 @@
 #else
 #include <sys/types.h>
 #endif
+#ifdef WIN32
+// TODO(jar): This is not needed when TCMalloc_PageMap1_LazyCommit has an API
+// supporting commit and reservation of memory.
+#include "common.h"
+#endif
+
 #include "internal_logging.h"  // for ASSERT
 
 // Single-level array
@@ -114,6 +120,201 @@ class TCMalloc_PageMap1 {
   }
 };
 
+#ifdef WIN32
+// Lazy commit, single-level array.
+// Very similar to PageMap1, except the page map is only committed as needed.
+// Since we don't return memory to the OS, the committed portion of the map will
+// only grow, and we'll only be called to Ensure when we really grow the heap.
+// We maintain a bit map to help us deduce if we've already committed a range
+// in our map.
+template <int BITS>
+class TCMalloc_PageMap1_LazyCommit {
+ private:
+  // Dimension of our page map array_.
+  static const int LENGTH = 1 << BITS;
+
+  // The page map array that sits in reserved virtual space.  Pages of this
+  // array are committed as they are needed.  For each page of virtual memory,
+  // we potentially have a pointer to a span instance.
+  void** array_;
+
+  // A bit vector that allows us to deduce what pages in array_ are committed.
+  // Note that 2^3 = 8 bits per char, and hence the use of the magical "3" in
+  // the array range gives us the effective "divide by 8".
+  char committed_[sizeof(void*) << (BITS - kPageShift - 3)];
+
+  // Given an |index| into |array_|, find the page number in |array_| that holds
+  // that element.
+  size_t ContainingPage(size_t index) const {
+    return (index * sizeof(*array_)) >> kPageShift;
+  }
+
+  // Find out if the given page_num index in array_ is in committed memory.
+  bool IsCommitted(size_t page_num) const {
+    return committed_[page_num >> 3] & (1 << (page_num & 0x7));
+  }
+
+  // Remember that the given page_num index in array_ is in committed memory.
+  void SetCommitted(size_t page_num) {
+    committed_[page_num >> 3] |= (1 << (page_num & 0x7));
+  }
+
+ public:
+  typedef uintptr_t Number;
+
+  explicit TCMalloc_PageMap1_LazyCommit(void* (*allocator)(size_t)) {
+    // TODO(jar): We need a reservation function, but current API to this class
+    // only provides an allocator.
+    // Get decommitted memory.  We will commit as necessary.
+    array_ = reinterpret_cast<void**>(VirtualAlloc(
+        NULL, sizeof(*array_) << BITS, MEM_RESERVE, PAGE_READWRITE));
+
+    // Make sure we divided LENGTH evenly.
+    ASSERT(sizeof(committed_) * 8 == (LENGTH * sizeof(*array_)) >> kPageShift);
+    // Indicate that none of the pages of array_ have been committed yet.
+    memset(committed_, 0, sizeof(committed_));
+  }
+
+  // Ensure that the map contains initialized and committed entries in array_ to
+  // describe pages "x .. x+n-1".
+  // Returns true if successful, false if we could not ensure this.
+  // If we have to commit more memory in array_ (which also clears said memory),
+  // then we'll set some of the bits in committed_ to remember this fact.
+  // Only the bits of committed_ near end-points for calls to Ensure() are ever
+  // set, as the calls to Ensure() will never have overlapping ranges other than
+  // at their end-points.
+  //
+  // Example: Suppose the OS allocates memory in pages including 40...50, and
+  // later the OS allocates memory in pages 51...83.  When the first allocation
+  // of 40...50 is observed, then Ensure of (39,51) will be called.  The range
+  // shown in the arguments is extended so that tcmalloc can look to see if
+  // adjacent pages are part of a span that can be coaleced.  Later, when pages
+  // 51...83 are allocated, Ensure() will be called with arguments (50,84),
+  // broadened again for the same reason.
+  //
+  // After the above, we would NEVER get a call such as Ensure(45,60), as that
+  // overlaps with the interior of prior ensured regions.  We ONLY get an Ensure
+  // call when the OS has allocated memory, and since we NEVER give memory back
+  // to the OS, the OS can't possible allocate the same region to us twice, and
+  // can't induce an Ensure() on an interior of previous Ensure call.
+  //
+  // Also note that OS allocations are NOT guaranteed to be consecutive (there
+  // may be "holes" where code etc. uses the virtual addresses), or to appear in
+  // any order, such as lowest to highest, or vice versa (as other independent
+  // allocation systems in the process may be performing VirtualAllocations and
+  // VirtualFrees asynchronously.)
+  bool Ensure(Number x, size_t n) {
+    if (n > LENGTH - x)
+      return false;  // We won't Ensure mapping for last pages in memory.
+    ASSERT(n > 0);
+
+    // For a given page number in memory, calculate what page in array_ needs to
+    // be memory resident.  Note that we really only need a few bytes in array_
+    // for each page of virtual space we have to map, but we can only commit
+    // whole pages of array_.  For instance, a 4K page of array_ has about 1k
+    // entries, and hence can map about 1K pages, or a total of about 4MB
+    // typically. As a result, it is possible that the first entry in array_,
+    // and the n'th entry in array_, will sit in the same page of array_.
+    size_t first_page = ContainingPage(x);
+    size_t last_page = ContainingPage(x + n - 1);
+
+    // Check at each boundary, to see if we need to commit at that end.  Some
+    // other neighbor may have already forced us to commit at either or both
+    // boundaries.
+    if (IsCommitted(first_page)) {
+      if (first_page == last_page) return true;
+      ++first_page;
+      if (IsCommitted(first_page)) {
+        if (first_page == last_page) return true;
+        ++first_page;
+      }
+    }
+
+    if (IsCommitted(last_page)) {
+      if (first_page == last_page) return true;
+      --last_page;
+      if (IsCommitted(last_page)) {
+        if (first_page == last_page) return true;
+        --last_page;
+      }
+    }
+
+    ASSERT(!IsCommitted(last_page));
+    ASSERT(!IsCommitted(first_page));
+
+    void* start = reinterpret_cast<char*>(array_) + (first_page << kPageShift);
+    size_t length = (last_page - first_page + 1) << kPageShift;
+
+#ifndef NDEBUG
+    // Validate we are committing new sections, and hence we're not clearing any
+    // existing data.
+    MEMORY_BASIC_INFORMATION info = {0};
+    size_t result = VirtualQuery(start, &info, sizeof(info));
+    ASSERT(result);
+    ASSERT(0 == (info.State & MEM_COMMIT));  // It starts with uncommitted.
+    ASSERT(info.RegionSize >= length);       // Entire length is uncommitted.
+#endif
+
+    // TODO(jar): We need a commit that automatically tallies metadata_bytes.
+    TCMalloc_SystemCommit(start, length);
+    tcmalloc::increment_metadata_system_bytes(length);
+
+#ifndef NDEBUG
+    result = VirtualQuery(start, &info, sizeof(info));
+    ASSERT(result);
+    ASSERT(0 != (info.State & MEM_COMMIT));  // Now it is committed.
+    ASSERT(info.RegionSize >= length);       // Entire length is committed.
+#endif
+
+    // As noted in the large comment/example describing this method, we will
+    // never be called with a range of pages very much inside this |first_page|
+    // to |last_page| range.
+    // As a result, we only need to set bits for each end of that range, and one
+    // page inside each end.
+    SetCommitted(first_page);
+    if (first_page < last_page) {
+      SetCommitted(last_page);
+      SetCommitted(first_page + 1);  // These may be duplicates now.
+      SetCommitted(last_page - 1);
+    }
+
+    return true;
+  }
+
+  // This is a premature call to get all the meta-memory allocated, so as to
+  // avoid virtual space fragmentation.  Since we pre-reserved all memory, we
+  // don't need to do anything here (we won't fragment virtual space).
+  void PreallocateMoreMemory() {}
+
+  // Return the current value for KEY.  Returns NULL if not yet set,
+  // or if k is out of range.
+  void* get(Number k) const {
+    if ((k >> BITS) > 0) {
+      return NULL;
+    }
+    return array_[k];
+  }
+
+  // REQUIRES "k" is in range "[0,2^BITS-1]".
+  // REQUIRES "k" has been ensured before.
+  //
+  // Sets the value for KEY.
+  void set(Number k, void* v) {
+    array_[k] = v;
+  }
+  // Return the first non-NULL pointer found in this map for
+  // a page number >= k.  Returns NULL if no such number is found.
+  void* Next(Number k) const {
+    while (k < (1 << BITS)) {
+      if (array_[k] != NULL) return array_[k];
+      k++;
+    }
+    return NULL;
+  }
+};
+#endif  // WIN32
+
+
 // Two-level radix tree
 template <int BITS>
 class TCMalloc_PageMap2 {