content: Release all free discardable memory when idle.

content/common/discardable_shared_memory_heap.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/discardable_shared_memory_heap.h"
 
 #include "base/memory/discardable_shared_memory.h"
 
 namespace content {
 namespace {
@@ skipping 11 matching lines @@
 DiscardableSharedMemoryHeap::Span::Span(
     base::DiscardableSharedMemory* shared_memory,
     size_t start,
     size_t length)
     : shared_memory_(shared_memory), start_(start), length_(length) {
 }
 
 DiscardableSharedMemoryHeap::Span::~Span() {
 }
 
+DiscardableSharedMemoryHeap::ScopedMemorySegment::ScopedMemorySegment(
+    DiscardableSharedMemoryHeap* heap,
+    scoped_ptr<base::DiscardableSharedMemory> shared_memory,
+    size_t size)
+    : heap_(heap), shared_memory_(shared_memory.Pass()), size_(size) {
+}
+
+DiscardableSharedMemoryHeap::ScopedMemorySegment::~ScopedMemorySegment() {
+  heap_->ReleaseMemory(shared_memory_.get(), size_);
+  // Purge memory. This has no effect if already purged.
+  shared_memory_->Purge(base::Time::Now());
+}
+
+bool DiscardableSharedMemoryHeap::ScopedMemorySegment::IsUsed() const {
+  return heap_->IsMemoryUsed(shared_memory_.get(), size_);
+}
+
+bool DiscardableSharedMemoryHeap::ScopedMemorySegment::IsResident() const {
+  return heap_->IsMemoryResident(shared_memory_.get());
+}
+
 DiscardableSharedMemoryHeap::DiscardableSharedMemoryHeap(size_t block_size)
-    : block_size_(block_size) {
+    : block_size_(block_size), num_blocks_(0), num_free_blocks_(0) {
   DCHECK_NE(block_size_, 0u);
   DCHECK(IsPowerOfTwo(block_size_));
 }
 
 DiscardableSharedMemoryHeap::~DiscardableSharedMemoryHeap() {
-  for (auto shared_memory : shared_memory_segments_)
-    ReleaseMemory(shared_memory);
-
+  memory_segments_.clear();
+  DCHECK_EQ(num_blocks_, 0u);
+  DCHECK_EQ(num_free_blocks_, 0u);
   DCHECK(free_spans_.empty());
 }
 
 scoped_ptr<DiscardableSharedMemoryHeap::Span> DiscardableSharedMemoryHeap::Grow(
     scoped_ptr<base::DiscardableSharedMemory> shared_memory,
     size_t size) {
   // Memory must be aligned to block size.
   DCHECK_EQ(
       reinterpret_cast<size_t>(shared_memory->memory()) & (block_size_ - 1),
       0u);
   DCHECK_EQ(size & (block_size_ - 1), 0u);
 
   scoped_ptr<Span> span(
       new Span(shared_memory.get(),
                reinterpret_cast<size_t>(shared_memory->memory()) / block_size_,
                size / block_size_));
   DCHECK(spans_.find(span->start_) == spans_.end());
   DCHECK(spans_.find(span->start_ + span->length_ - 1) == spans_.end());
   RegisterSpan(span.get());
 
-  // Start tracking if segment is resident by adding it to
-  // |shared_memory_segments_|.
-  shared_memory_segments_.push_back(shared_memory.release());
+  num_blocks_ += span->length_;
+
+  // Start tracking if segment is resident by adding it to |memory_segments_|.
+  memory_segments_.push_back(
+      new ScopedMemorySegment(this, shared_memory.Pass(), size));
 
   return span.Pass();
 }
 
 void DiscardableSharedMemoryHeap::MergeIntoFreeList(scoped_ptr<Span> span) {
   DCHECK(span->shared_memory_);
 
+  // First add length of |span| to |num_free_blocks_|.
+  num_free_blocks_ += span->length_;
+
   // Merge with previous span if possible.
   SpanMap::iterator prev_it = spans_.find(span->start_ - 1);
   if (prev_it != spans_.end() && IsInFreeList(prev_it->second)) {
     scoped_ptr<Span> prev = RemoveFromFreeList(prev_it->second);
     DCHECK_EQ(prev->start_ + prev->length_, span->start_);
     UnregisterSpan(prev.get());
     if (span->length_ > 1)
       spans_.erase(span->start_);
     span->start_ -= prev->length_;
     span->length_ += prev->length_;
@@ skipping 53 matching lines @@
       if ((span->length_ == best->length_) && (span->start_ > best->start_))
         continue;
     }
 
     best = span;
   }
 
   return best ? Carve(best, blocks) : nullptr;
 }
 
-size_t DiscardableSharedMemoryHeap::ReleaseFreeMemory() {
-  size_t bytes_released = 0;
-  size_t i = 0;
+void DiscardableSharedMemoryHeap::ReleaseFreeMemory() {
+  // Erase all free segments after rearranging the segments in such a way
+  // that used segments precede all free segments.
+  memory_segments_.erase(
+      std::partition(
+          memory_segments_.begin(), memory_segments_.end(),
+          [](const ScopedMemorySegment* segment) { return segment->IsUsed(); }),
+      memory_segments_.end());
+}
 
-  // Release memory for all non-resident segments.
-  while (i < shared_memory_segments_.size()) {
-    base::DiscardableSharedMemory* shared_memory = shared_memory_segments_[i];
+void DiscardableSharedMemoryHeap::ReleasePurgedMemory() {
+  // Erase all purged segments after rearranging the segments in such a way
+  // that resident segments precede all purged segments.
+  memory_segments_.erase(
+      std::partition(memory_segments_.begin(), memory_segments_.end(),
+                     [](const ScopedMemorySegment* segment) {
+                       return segment->IsResident();
+                     }),
+      memory_segments_.end());
+}
 
-    // Skip segment if still resident.
-    if (shared_memory->IsMemoryResident()) {
-      ++i;
-      continue;
-    }
+size_t DiscardableSharedMemoryHeap::GetSize() const {
+  return num_blocks_ * block_size_;
+}
 
-    bytes_released += shared_memory->mapped_size();
-
-    // Release the memory and unregistering all associated spans.
-    ReleaseMemory(shared_memory);
-
-    std::swap(shared_memory_segments_[i], shared_memory_segments_.back());
-    shared_memory_segments_.pop_back();
-  }
-
-  return bytes_released;
+size_t DiscardableSharedMemoryHeap::GetFreeListSize() const {
+  return num_free_blocks_ * block_size_;
 }
 
 scoped_ptr<DiscardableSharedMemoryHeap::Span>
 DiscardableSharedMemoryHeap::RemoveFromFreeList(Span* span) {
   span->RemoveFromList();
   return make_scoped_ptr(span);
 }
 
 scoped_ptr<DiscardableSharedMemoryHeap::Span>
 DiscardableSharedMemoryHeap::Carve(Span* span, size_t blocks) {
   scoped_ptr<Span> serving = RemoveFromFreeList(span);
 
   const int extra = serving->length_ - blocks;
   if (extra) {
     scoped_ptr<Span> leftover(
         new Span(serving->shared_memory_, serving->start_ + blocks, extra));
     DCHECK_IMPLIES(extra > 1, spans_.find(leftover->start_) == spans_.end());
     RegisterSpan(leftover.get());
 
     // No need to coalesce as the previous span of |leftover| was just split
     // and the next span of |leftover| was not previously coalesced with
     // |span|.
     free_spans_.Append(leftover.release());
 
     serving->length_ = blocks;
     spans_[serving->start_ + blocks - 1] = serving.get();
   }
 
+  // |serving| is no longer in the free list, remove its length from
+  // |num_free_blocks_|.
+  DCHECK_GE(num_free_blocks_, serving->length_);
+  num_free_blocks_ -= serving->length_;
+
   return serving.Pass();
 }
 
 void DiscardableSharedMemoryHeap::RegisterSpan(Span* span) {
   spans_[span->start_] = span;
   if (span->length_ > 1)
     spans_[span->start_ + span->length_ - 1] = span;
 }
 
 void DiscardableSharedMemoryHeap::UnregisterSpan(Span* span) {
   DCHECK(spans_.find(span->start_) != spans_.end());
   DCHECK_EQ(spans_[span->start_], span);
   spans_.erase(span->start_);
   if (span->length_ > 1) {
     DCHECK(spans_.find(span->start_ + span->length_ - 1) != spans_.end());
     DCHECK_EQ(spans_[span->start_ + span->length_ - 1], span);
     spans_.erase(span->start_ + span->length_ - 1);
   }
 }
 
-void DiscardableSharedMemoryHeap::ReleaseMemory(
-    base::DiscardableSharedMemory* shared_memory) {
+bool DiscardableSharedMemoryHeap::IsMemoryUsed(
+    const base::DiscardableSharedMemory* shared_memory,
+    size_t size) {
   size_t offset =
       reinterpret_cast<size_t>(shared_memory->memory()) / block_size_;
-  size_t end = offset + shared_memory->mapped_size() / block_size_;
+  size_t length = size / block_size_;
+  DCHECK(spans_.find(offset) != spans_.end());
+  Span* span = spans_[offset];
+  DCHECK_LE(span->length_, length);
+  // Memory is used if first span is not in free list or shorter than segment.
+  return !IsInFreeList(span) || span->length_ != length;
+}
+
+bool DiscardableSharedMemoryHeap::IsMemoryResident(
+    const base::DiscardableSharedMemory* shared_memory) {
+  return shared_memory->IsMemoryResident();
+}
+
+void DiscardableSharedMemoryHeap::ReleaseMemory(
+    const base::DiscardableSharedMemory* shared_memory,
+    size_t size) {
+  size_t offset =
+      reinterpret_cast<size_t>(shared_memory->memory()) / block_size_;
+  size_t end = offset + size / block_size_;
   while (offset < end) {
     DCHECK(spans_.find(offset) != spans_.end());
     Span* span = spans_[offset];
     DCHECK_EQ(span->shared_memory_, shared_memory);
     span->shared_memory_ = nullptr;
     UnregisterSpan(span);
 
     offset += span->length_;
 
-    // If |span| is in the free list, remove it.
-    if (IsInFreeList(span))
+    DCHECK_GE(num_blocks_, span->length_);
+    num_blocks_ -= span->length_;
+
+    // If |span| is in the free list, remove it and update |num_free_blocks_|.
+    if (IsInFreeList(span)) {
+      DCHECK_GE(num_free_blocks_, span->length_);
+      num_free_blocks_ -= span->length_;
       RemoveFromFreeList(span);
+    }
   }
 }
 
 }  // namespace content