Upgrade gperftools to 2.9 for GCP/GMC/GMP/GMD. (#2247)

trunk/3rdparty/gperftools-2-fit/src/page_heap.cc

@@ -0,0 +1,718 @@
+// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+// 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
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// ---
+// Author: Sanjay Ghemawat <opensource@google.com>
+
+#include <config.h>
+#ifdef HAVE_INTTYPES_H
+#include <inttypes.h>                   // for PRIuPTR
+#endif
+#include <errno.h>                      // for ENOMEM, errno
+#include <gperftools/malloc_extension.h>      // for MallocRange, etc
+#include "base/basictypes.h"
+#include "base/commandlineflags.h"
+#include "internal_logging.h"  // for ASSERT, TCMalloc_Printer, etc
+#include "page_heap_allocator.h"  // for PageHeapAllocator
+#include "static_vars.h"       // for Static
+#include "system-alloc.h"      // for TCMalloc_SystemAlloc, etc
+
+DEFINE_double(tcmalloc_release_rate,
+              EnvToDouble("TCMALLOC_RELEASE_RATE", 1.0),
+              "Rate at which we release unused memory to the system.  "
+              "Zero means we never release memory back to the system.  "
+              "Increase this flag to return memory faster; decrease it "
+              "to return memory slower.  Reasonable rates are in the "
+              "range [0,10]");
+
+DEFINE_int64(tcmalloc_heap_limit_mb,
+              EnvToInt("TCMALLOC_HEAP_LIMIT_MB", 0),
+              "Limit total size of the process heap to the "
+              "specified number of MiB. "
+              "When we approach the limit the memory is released "
+              "to the system more aggressively (more minor page faults). "
+              "Zero means to allocate as long as system allows.");
+
+namespace tcmalloc {
+
+PageHeap::PageHeap()
+    : pagemap_(MetaDataAlloc),
+      scavenge_counter_(0),
+      // Start scavenging at kMaxPages list
+      release_index_(kMaxPages),
+      aggressive_decommit_(false) {
+  COMPILE_ASSERT(kClassSizesMax <= (1 << PageMapCache::kValuebits), valuebits);
+  for (int i = 0; i < kMaxPages; i++) {
+    DLL_Init(&free_[i].normal);
+    DLL_Init(&free_[i].returned);
+  }
+}
+
+Span* PageHeap::SearchFreeAndLargeLists(Length n) {
+  ASSERT(Check());
+  ASSERT(n > 0);
+
+  // Find first size >= n that has a non-empty list
+  for (Length s = n; s <= kMaxPages; s++) {
+    Span* ll = &free_[s - 1].normal;
+    // If we're lucky, ll is non-empty, meaning it has a suitable span.
+    if (!DLL_IsEmpty(ll)) {
+      ASSERT(ll->next->location == Span::ON_NORMAL_FREELIST);
+      return Carve(ll->next, n);
+    }
+    // Alternatively, maybe there's a usable returned span.
+    ll = &free_[s - 1].returned;
+    if (!DLL_IsEmpty(ll)) {
+      // We did not call EnsureLimit before, to avoid releasing the span
+      // that will be taken immediately back.
+      // Calling EnsureLimit here is not very expensive, as it fails only if
+      // there is no more normal spans (and it fails efficiently)
+      // or SystemRelease does not work (there is probably no returned spans).
+      if (EnsureLimit(n)) {
+        // ll may have became empty due to coalescing
+        if (!DLL_IsEmpty(ll)) {
+          ASSERT(ll->next->location == Span::ON_RETURNED_FREELIST);
+          return Carve(ll->next, n);
+        }
+      }
+    }
+  }
+  // No luck in free lists, our last chance is in a larger class.
+  return AllocLarge(n);  // May be NULL
+}
+
+static const size_t kForcedCoalesceInterval = 128*1024*1024;
+
+Span* PageHeap::New(Length n) {
+  ASSERT(Check());
+  ASSERT(n > 0);
+
+  Span* result = SearchFreeAndLargeLists(n);
+  if (result != NULL)
+    return result;
+
+  if (stats_.free_bytes != 0 && stats_.unmapped_bytes != 0
+      && stats_.free_bytes + stats_.unmapped_bytes >= stats_.system_bytes / 4
+      && (stats_.system_bytes / kForcedCoalesceInterval
+          != (stats_.system_bytes + (n << kPageShift)) / kForcedCoalesceInterval)) {
+    // We're about to grow heap, but there are lots of free pages.
+    // tcmalloc's design decision to keep unmapped and free spans
+    // separately and never coalesce them means that sometimes there
+    // can be free pages span of sufficient size, but it consists of
+    // "segments" of different type so page heap search cannot find
+    // it. In order to prevent growing heap and wasting memory in such
+    // case we're going to unmap all free pages. So that all free
+    // spans are maximally coalesced.
+    //
+    // We're also limiting 'rate' of going into this path to be at
+    // most once per 128 megs of heap growth. Otherwise programs that
+    // grow heap frequently (and that means by small amount) could be
+    // penalized with higher count of minor page faults.
+    //
+    // See also large_heap_fragmentation_unittest.cc and
+    // https://code.google.com/p/gperftools/issues/detail?id=368
+    ReleaseAtLeastNPages(static_cast<Length>(0x7fffffff));
+
+    // then try again. If we are forced to grow heap because of large
+    // spans fragmentation and not because of problem described above,
+    // then at the very least we've just unmapped free but
+    // insufficiently big large spans back to OS. So in case of really
+    // unlucky memory fragmentation we'll be consuming virtual address
+    // space, but not real memory
+    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());
+    // underlying SysAllocator likely set ENOMEM but we can get here
+    // due to EnsureLimit so we set it here too.
+    //
+    // Setting errno to ENOMEM here allows us to avoid dealing with it
+    // in fast-path.
+    errno = ENOMEM;
+    return NULL;
+  }
+  return SearchFreeAndLargeLists(n);
+}
+
+Span* PageHeap::AllocLarge(Length n) {
+  Span *best = NULL;
+  Span *best_normal = NULL;
+
+  // Create a Span to use as an upper bound.
+  Span bound;
+  bound.start = 0;
+  bound.length = n;
+
+  // First search the NORMAL spans..
+  SpanSet::iterator place = large_normal_.upper_bound(SpanPtrWithLength(&bound));
+  if (place != large_normal_.end()) {
+    best = place->span;
+    best_normal = best;
+    ASSERT(best->location == Span::ON_NORMAL_FREELIST);
+  }
+
+  // Try to find better fit from RETURNED spans.
+  place = large_returned_.upper_bound(SpanPtrWithLength(&bound));
+  if (place != large_returned_.end()) {
+    Span *c = place->span;
+    ASSERT(c->location == Span::ON_RETURNED_FREELIST);
+    if (best_normal == NULL
+        || c->length < best->length
+        || (c->length == best->length && c->start < best->start))
+      best = place->span;
+  }
+
+  if (best == best_normal) {
+    return best == NULL ? NULL : Carve(best, n);
+  }
+
+  // best comes from RETURNED set.
+
+  if (EnsureLimit(n, false)) {
+    return Carve(best, n);
+  }
+
+  if (EnsureLimit(n, true)) {
+    // best could have been destroyed by coalescing.
+    // best_normal is not a best-fit, and it could be destroyed as well.
+    // We retry, the limit is already ensured:
+    return AllocLarge(n);
+  }
+
+  // If best_normal existed, EnsureLimit would succeeded:
+  ASSERT(best_normal == NULL);
+  // We are not allowed to take best from returned list.
+  return NULL;
+}
+
+Span* PageHeap::Split(Span* span, Length n) {
+  ASSERT(0 < n);
+  ASSERT(n < span->length);
+  ASSERT(span->location == Span::IN_USE);
+  ASSERT(span->sizeclass == 0);
+
+  const int extra = span->length - n;
+  Span* leftover = NewSpan(span->start + n, extra);
+  ASSERT(leftover->location == Span::IN_USE);
+  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) {
+  ++stats_.commit_count;
+
+  TCMalloc_SystemCommit(reinterpret_cast<void*>(span->start << kPageShift),
+                        static_cast<size_t>(span->length << kPageShift));
+  stats_.committed_bytes += span->length << kPageShift;
+  stats_.total_commit_bytes += (span->length << kPageShift);
+}
+
+bool PageHeap::DecommitSpan(Span* span) {
+  ++stats_.decommit_count;
+
+  bool rv = TCMalloc_SystemRelease(reinterpret_cast<void*>(span->start << kPageShift),
+                                   static_cast<size_t>(span->length << kPageShift));
+  if (rv) {
+    stats_.committed_bytes -= span->length << kPageShift;
+    stats_.total_decommit_bytes += (span->length << kPageShift);
+  }
+
+  return rv;
+}
+
+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;
+
+  const int extra = span->length - n;
+  ASSERT(extra >= 0);
+  if (extra > 0) {
+    Span* leftover = NewSpan(span->start + n, extra);
+    leftover->location = old_location;
+    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|.
+#ifndef NDEBUG
+    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);
+#endif
+
+    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;
+  MergeIntoFreeList(span);  // Coalesces if possible
+  IncrementalScavenge(n);
+  ASSERT(stats_.unmapped_bytes+ stats_.committed_bytes==stats_.system_bytes);
+  ASSERT(Check());
+}
+
+// Given span we're about to free and other span (still on free list),
+// checks if 'other' span is mergable with 'span'. If it is, removes
+// other span from free list, performs aggressive decommit if
+// necessary and returns 'other' span. Otherwise 'other' span cannot
+// be merged and is left untouched. In that case NULL is returned.
+Span* PageHeap::CheckAndHandlePreMerge(Span* span, Span* other) {
+  if (other == NULL) {
+    return other;
+  }
+  // if we're in aggressive decommit mode and span is decommitted,
+  // then we try to decommit adjacent span.
+  if (aggressive_decommit_ && other->location == Span::ON_NORMAL_FREELIST
+      && span->location == Span::ON_RETURNED_FREELIST) {
+    bool worked = DecommitSpan(other);
+    if (!worked) {
+      return NULL;
+    }
+  } else if (other->location != span->location) {
+    return NULL;
+  }
+
+  RemoveFromFreeList(other);
+  return other;
+}
+
+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: depending on aggressive_decommit_ mode we allow only
+  // similar spans to be coalesced.
+  //
+  // The following applies if aggressive_decommit_ is enabled:
+  //
+  // 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;
+
+  if (aggressive_decommit_ && span->location == Span::ON_NORMAL_FREELIST) {
+    if (DecommitSpan(span)) {
+      span->location = Span::ON_RETURNED_FREELIST;
+    }
+  }
+
+  Span* prev = CheckAndHandlePreMerge(span, GetDescriptor(p-1));
+  if (prev != NULL) {
+    // Merge preceding span into this span
+    ASSERT(prev->start + prev->length == p);
+    const Length len = prev->length;
+    DeleteSpan(prev);
+    span->start -= len;
+    span->length += len;
+    pagemap_.set(span->start, span);
+  }
+  Span* next = CheckAndHandlePreMerge(span, GetDescriptor(p+n));
+  if (next != NULL) {
+    // Merge next span into this span
+    ASSERT(next->start == p+n);
+    const Length len = next->length;
+    DeleteSpan(next);
+    span->length += len;
+    pagemap_.set(span->start + span->length - 1, span);
+  }
+
+  PrependToFreeList(span);
+}
+
+void PageHeap::PrependToFreeList(Span* span) {
+  ASSERT(span->location != Span::IN_USE);
+  if (span->location == Span::ON_NORMAL_FREELIST)
+    stats_.free_bytes += (span->length << kPageShift);
+  else
+    stats_.unmapped_bytes += (span->length << kPageShift);
+
+  if (span->length > kMaxPages) {
+    SpanSet *set = &large_normal_;
+    if (span->location == Span::ON_RETURNED_FREELIST)
+      set = &large_returned_;
+    std::pair<SpanSet::iterator, bool> p =
+        set->insert(SpanPtrWithLength(span));
+    ASSERT(p.second); // We never have duplicates since span->start is unique.
+    span->SetSpanSetIterator(p.first);
+    return;
+  }
+
+  SpanList* list = &free_[span->length - 1];
+  if (span->location == Span::ON_NORMAL_FREELIST) {
+    DLL_Prepend(&list->normal, span);
+  } else {
+    DLL_Prepend(&list->returned, span);
+  }
+}
+
+void PageHeap::RemoveFromFreeList(Span* span) {
+  ASSERT(span->location != Span::IN_USE);
+  if (span->location == Span::ON_NORMAL_FREELIST) {
+    stats_.free_bytes -= (span->length << kPageShift);
+  } else {
+    stats_.unmapped_bytes -= (span->length << kPageShift);
+  }
+  if (span->length > kMaxPages) {
+    SpanSet *set = &large_normal_;
+    if (span->location == Span::ON_RETURNED_FREELIST)
+      set = &large_returned_;
+    SpanSet::iterator iter = span->ExtractSpanSetIterator();
+    ASSERT(iter->span == span);
+    ASSERT(set->find(SpanPtrWithLength(span)) == iter);
+    set->erase(iter);
+  } else {
+    DLL_Remove(span);
+  }
+}
+
+void PageHeap::IncrementalScavenge(Length n) {
+  // Fast path; not yet time to release memory
+  scavenge_counter_ -= n;
+  if (scavenge_counter_ >= 0) return;  // Not yet time to scavenge
+
+  const double rate = FLAGS_tcmalloc_release_rate;
+  if (rate <= 1e-6) {
+    // Tiny release rate means that releasing is disabled.
+    scavenge_counter_ = kDefaultReleaseDelay;
+    return;
+  }
+
+  ++stats_.scavenge_count;
+
+  Length released_pages = ReleaseAtLeastNPages(1);
+
+  if (released_pages == 0) {
+    // Nothing to scavenge, delay for a while.
+    scavenge_counter_ = kDefaultReleaseDelay;
+  } else {
+    // Compute how long to wait until we return memory.
+    // FLAGS_tcmalloc_release_rate==1 means wait for 1000 pages
+    // after releasing one page.
+    const double mult = 1000.0 / rate;
+    double wait = mult * static_cast<double>(released_pages);
+    if (wait > kMaxReleaseDelay) {
+      // Avoid overflow and bound to reasonable range.
+      wait = kMaxReleaseDelay;
+    }
+    scavenge_counter_ = static_cast<int64_t>(wait);
+  }
+}
+
+Length PageHeap::ReleaseSpan(Span* s) {
+  ASSERT(s->location == Span::ON_NORMAL_FREELIST);
+
+  if (DecommitSpan(s)) {
+    RemoveFromFreeList(s);
+    const Length n = s->length;
+    s->location = Span::ON_RETURNED_FREELIST;
+    MergeIntoFreeList(s);  // Coalesces if possible.
+    return n;
+  }
+
+  return 0;
+}
+
+Length PageHeap::ReleaseAtLeastNPages(Length num_pages) {
+  Length released_pages = 0;
+
+  // Round robin through the lists of free spans, releasing a
+  // span from each list.  Stop after releasing at least num_pages
+  // or when there is nothing more to release.
+  while (released_pages < num_pages && stats_.free_bytes > 0) {
+    for (int i = 0; i < kMaxPages+1 && released_pages < num_pages;
+         i++, release_index_++) {
+      Span *s;
+      if (release_index_ > kMaxPages) release_index_ = 0;
+
+      if (release_index_ == kMaxPages) {
+        if (large_normal_.empty()) {
+          continue;
+        }
+        s = (large_normal_.begin())->span;
+      } else {
+        SpanList* slist = &free_[release_index_];
+        if (DLL_IsEmpty(&slist->normal)) {
+          continue;
+        }
+        s = slist->normal.prev;
+      }
+      // TODO(todd) if the remaining number of pages to release
+      // is significantly smaller than s->length, and s is on the
+      // large freelist, should we carve s instead of releasing?
+      // the whole thing?
+      Length released_len = ReleaseSpan(s);
+      // Some systems do not support release
+      if (released_len == 0) return released_pages;
+      released_pages += released_len;
+    }
+  }
+  return released_pages;
+}
+
+bool PageHeap::EnsureLimit(Length n, bool withRelease)
+{
+  Length limit = (FLAGS_tcmalloc_heap_limit_mb*1024*1024) >> kPageShift;
+  if (limit == 0) return true; //there is no limit
+
+  // We do not use stats_.system_bytes because it does not take
+  // MetaDataAllocs into account.
+  Length takenPages = TCMalloc_SystemTaken >> kPageShift;
+  //XXX takenPages may be slightly bigger than limit for two reasons:
+  //* MetaDataAllocs ignore the limit (it is not easy to handle
+  //  out of memory there)
+  //* sys_alloc may round allocation up to huge page size,
+  //  although smaller limit was ensured
+
+  ASSERT(takenPages >= stats_.unmapped_bytes >> kPageShift);
+  takenPages -= stats_.unmapped_bytes >> kPageShift;
+
+  if (takenPages + n > limit && withRelease) {
+    takenPages -= ReleaseAtLeastNPages(takenPages + n - limit);
+  }
+
+  return takenPages + n <= limit;
+}
+
+void PageHeap::RegisterSizeClass(Span* span, uint32 sc) {
+  // Associate span object with all interior pages as well
+  ASSERT(span->location == Span::IN_USE);
+  ASSERT(GetDescriptor(span->start) == span);
+  ASSERT(GetDescriptor(span->start+span->length-1) == span);
+  span->sizeclass = sc;
+  for (Length i = 1; i < span->length-1; i++) {
+    pagemap_.set(span->start+i, span);
+  }
+}
+
+void PageHeap::GetSmallSpanStats(SmallSpanStats* result) {
+  for (int i = 0; i < kMaxPages; i++) {
+    result->normal_length[i] = DLL_Length(&free_[i].normal);
+    result->returned_length[i] = DLL_Length(&free_[i].returned);
+  }
+}
+
+void PageHeap::GetLargeSpanStats(LargeSpanStats* result) {
+  result->spans = 0;
+  result->normal_pages = 0;
+  result->returned_pages = 0;
+  for (SpanSet::iterator it = large_normal_.begin(); it != large_normal_.end(); ++it) {
+    result->normal_pages += it->length;
+    result->spans++;
+  }
+  for (SpanSet::iterator it = large_returned_.begin(); it != large_returned_.end(); ++it) {
+    result->returned_pages += it->length;
+    result->spans++;
+  }
+}
+
+bool PageHeap::GetNextRange(PageID start, base::MallocRange* r) {
+  Span* span = reinterpret_cast<Span*>(pagemap_.Next(start));
+  if (span == NULL) {
+    return false;
+  }
+  r->address = span->start << kPageShift;
+  r->length = span->length << kPageShift;
+  r->fraction = 0;
+  switch (span->location) {
+    case Span::IN_USE:
+      r->type = base::MallocRange::INUSE;
+      r->fraction = 1;
+      if (span->sizeclass > 0) {
+        // Only some of the objects in this span may be in use.
+        const size_t osize = Static::sizemap()->class_to_size(span->sizeclass);
+        r->fraction = (1.0 * osize * span->refcount) / r->length;
+      }
+      break;
+    case Span::ON_NORMAL_FREELIST:
+      r->type = base::MallocRange::FREE;
+      break;
+    case Span::ON_RETURNED_FREELIST:
+      r->type = base::MallocRange::UNMAPPED;
+      break;
+    default:
+      r->type = base::MallocRange::UNKNOWN;
+      break;
+  }
+  return true;
+}
+
+static void RecordGrowth(size_t growth) {
+  StackTrace* t = Static::stacktrace_allocator()->New();
+  t->depth = GetStackTrace(t->stack, kMaxStackDepth-1, 3);
+  t->size = growth;
+  t->stack[kMaxStackDepth-1] = reinterpret_cast<void*>(Static::growth_stacks());
+  Static::set_growth_stacks(t);
+}
+
+bool PageHeap::GrowHeap(Length n) {
+  ASSERT(kMaxPages >= kMinSystemAlloc);
+  if (n > kMaxValidPages) return false;
+  Length ask = (n>kMinSystemAlloc) ? n : static_cast<Length>(kMinSystemAlloc);
+  size_t actual_size;
+  void* ptr = NULL;
+  if (EnsureLimit(ask)) {
+      ptr = TCMalloc_SystemAlloc(ask << kPageShift, &actual_size, kPageSize);
+  }
+  if (ptr == NULL) {
+    if (n < ask) {
+      // Try growing just "n" pages
+      ask = n;
+      if (EnsureLimit(ask)) {
+        ptr = TCMalloc_SystemAlloc(ask << kPageShift, &actual_size, kPageSize);
+      }
+    }
+    if (ptr == NULL) return false;
+  }
+  ask = actual_size >> kPageShift;
+  RecordGrowth(ask << kPageShift);
+
+  ++stats_.reserve_count;
+  ++stats_.commit_count;
+
+  uint64_t old_system_bytes = stats_.system_bytes;
+  stats_.system_bytes += (ask << kPageShift);
+  stats_.committed_bytes += (ask << kPageShift);
+
+  stats_.total_commit_bytes += (ask << kPageShift);
+  stats_.total_reserve_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() {
+  return true;
+}
+
+bool PageHeap::CheckExpensive() {
+  bool result = Check();
+  CheckSet(&large_normal_, kMaxPages + 1, Span::ON_NORMAL_FREELIST);
+  CheckSet(&large_returned_, kMaxPages + 1, Span::ON_RETURNED_FREELIST);
+  for (int s = 1; s <= kMaxPages; s++) {
+    CheckList(&free_[s - 1].normal, s, s, Span::ON_NORMAL_FREELIST);
+    CheckList(&free_[s - 1].returned, s, s, Span::ON_RETURNED_FREELIST);
+  }
+  return result;
+}
+
+bool PageHeap::CheckList(Span* list, Length min_pages, Length max_pages,
+                         int freelist) {
+  for (Span* s = list->next; s != list; s = s->next) {
+    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;
+}
+
+bool PageHeap::CheckSet(SpanSet* spanset, Length min_pages,int freelist) {
+  for (SpanSet::iterator it = spanset->begin(); it != spanset->end(); ++it) {
+    Span* s = it->span;
+    CHECK_CONDITION(s->length == it->length);
+    CHECK_CONDITION(s->location == freelist);  // NORMAL or RETURNED
+    CHECK_CONDITION(s->length >= min_pages);
+    CHECK_CONDITION(GetDescriptor(s->start) == s);
+    CHECK_CONDITION(GetDescriptor(s->start+s->length-1) == s);
+  }
+  return true;
+}
+
+}  // namespace tcmalloc