Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_provider.cc

+// Copyright 2013 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 "base/memory/discardable_memory_provider.h"
+
+#include "base/bind.h"
+#include "base/containers/hash_tables.h"
+#include "base/containers/mru_cache.h"
+#include "base/debug/trace_event.h"
+#include "base/memory/discardable_memory.h"
+#include "base/synchronization/lock.h"
+#include "base/sys_info.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+
+// If this is given a valid value via SetInstanceForTest, this pointer will be
+// returned by GetInstance rather than the usual singleton.
+static DiscardableMemoryProvider* s_provider_for_test = NULL;
+
+// This is admittedly pretty magical. It's approximately enough memory for two
+// 2560x1600 images.
+static const size_t kDefaultDiscardableMemoryLimit = 32 * 1024 * 1024;
+static const size_t kDefaultBytesToReclaimUnderModeratePressure =
+    kDefaultDiscardableMemoryLimit / 2;
+
+}  // namespace
+
+DiscardableMemoryProvider::DiscardableMemoryProvider()
+    : allocations_(AllocationMap::NO_AUTO_EVICT),
+      bytes_allocated_(0),
+      discardable_memory_limit_(kDefaultDiscardableMemoryLimit),
+      bytes_to_reclaim_under_moderate_pressure_(
+          kDefaultBytesToReclaimUnderModeratePressure),
+      enforcing_policy_(false),
+      memory_pressure_listener_(
+          base::Bind(&DiscardableMemoryProvider::NotifyMemoryPressure)) {
+}
+
+DiscardableMemoryProvider::~DiscardableMemoryProvider() {
+  DCHECK_EQ(0u, allocations_.size());
+  DCHECK_EQ(0u, bytes_allocated_);
+}
+
+// static
+DiscardableMemoryProvider* DiscardableMemoryProvider::GetInstance() {
+  if (s_provider_for_test)
+    return s_provider_for_test;
+  return Singleton<DiscardableMemoryProvider>::get();

[willchan no longer on Chromium, 2013/10/17 02:06:13]

WDYT about using a LeakyLazyInstance instead? Is there a good reason to delete
stuff on shutdown?

[reveman, 2013/10/19 21:17:04]

Not really. I guess we need to use a LeakyLazyInstance to allow the use of
Singleton<DiscardableMemory> but not sure that's necessary. Seems like there
would be a bit more code to use LeakyLazyInstance but I'll switch to that if
preferred?

[willchan no longer on Chromium, 2013/10/21 18:30:27]

Not deleting on shutdown is preferable. It avoids shutdown crashes (when not all
threads are joined) and makes shutdown quicker (less deletion means less work on
shutdown). If you need something done on shutdown, then by all means, use
LazyInstance/Singleton, but otherwise, make it leaky.

LazyInstance also helps avoids fragmentation by allocating in a global segment
rather than in heap.

[reveman, 2013/10/22 00:11:41]

Thanks for the explanation. That makes sense. It's now a leaky LazyInstance.

+}
+
+// static
+void DiscardableMemoryProvider::SetInstanceForTest(
+    DiscardableMemoryProvider* provider) {
+  s_provider_for_test = provider;
+}
+
+// static
+void DiscardableMemoryProvider::NotifyMemoryPressure(
+    MemoryPressureListener::MemoryPressureLevel pressure_level) {
+  switch (pressure_level) {
+    case MemoryPressureListener::MEMORY_PRESSURE_MODERATE:
+      DiscardableMemoryProvider::GetInstance()->Purge();
+      return;
+    case MemoryPressureListener::MEMORY_PRESSURE_CRITICAL:
+      DiscardableMemoryProvider::GetInstance()->PurgeAll();
+      return;
+  }
+
+  NOTREACHED();
+}
+
+void DiscardableMemoryProvider::SetDiscardableMemoryLimit(size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    discardable_memory_limit_ = bytes;
+  }
+  EnforcePolicy();
+}
+
+void DiscardableMemoryProvider::SetBytesToReclaimUnderModeratePressure(
+    size_t bytes) {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    bytes_to_reclaim_under_moderate_pressure_ = bytes;
+  }
+  EnforcePolicy();
+}
+
+void DiscardableMemoryProvider::Register(
+    const DiscardableMemory* discardable, size_t bytes) {
+  AutoLock lock(allocations_lock_);
+  DCHECK(allocations_.Peek(discardable) == allocations_.end());
+  allocations_.Put(discardable, Allocation(bytes));
+}
+
+void DiscardableMemoryProvider::Unregister(
+    const DiscardableMemory* discardable) {
+  AutoLock lock(allocations_lock_);

[willchan no longer on Chromium, 2013/10/17 02:06:13]

You acquire this lock here first. Later on, you may try to acquire
bytes_allocated_lock_ at line 108.

Purge() grabs bytes_allocated_lock_ first. And then allocations_lock_.

What happens when Unregister() and Purge() execute concurrently? Do we deadlock?

[reveman, 2013/10/19 21:17:04]

Yes, the use of multiple locks here is broken. Reduced it to just one lock in
latest patch, which makes everything much simpler and hopefully that's good
enough. vollick@, I assume the use of two locks in your original patch was for
performance reasons, correct? Did you do some testing to determine that this was
needed?

+  AllocationMap::iterator it = allocations_.Peek(discardable);
+  if (it == allocations_.end())
+    return;
+
+  if (it->second.memory) {
+    AutoLock bytes_lock(bytes_allocated_lock_);
+    size_t bytes = it->second.bytes;
+    DCHECK_LE(bytes, bytes_allocated_);
+    bytes_allocated_ -= bytes;
+    free(it->second.memory);
+  }
+  allocations_.Erase(it);
+}
+
+scoped_ptr<uint8, FreeDeleter> DiscardableMemoryProvider::Acquire(
+    const DiscardableMemory* discardable,
+    bool* purged) {
+  AutoLock lock(allocations_lock_);
+  // NB: |allocations_| is an MRU cache, and use of |Get| here updates that
+  // cache.
+  AllocationMap::iterator it = allocations_.Get(discardable);
+  CHECK(it != allocations_.end());
+
+  if (it->second.memory) {
+    scoped_ptr<uint8, FreeDeleter> memory(it->second.memory);
+    it->second.memory = NULL;
+    *purged = false;
+    return memory.Pass();
+  }
+
+  size_t bytes = it->second.bytes;
+  if (!bytes)
+    return scoped_ptr<uint8, FreeDeleter>();
+
+  AutoLock bytes_lock(bytes_allocated_lock_);
+
+  if (discardable_memory_limit_) {
+    if (bytes > discardable_memory_limit_)
+      return scoped_ptr<uint8, FreeDeleter>();
+
+    size_t limit = discardable_memory_limit_ - bytes;
+    PurgeLRU(limit);
+
+    if (bytes_allocated_ > limit)
+      return scoped_ptr<uint8, FreeDeleter>();
+  }
+
+  bytes_allocated_ += bytes;
+  *purged = true;
+  return scoped_ptr<uint8, FreeDeleter>(static_cast<uint8*>(malloc(bytes)));
+}
+
+void DiscardableMemoryProvider::Release(
+    const DiscardableMemory* discardable,
+    scoped_ptr<uint8, FreeDeleter> memory) {
+  {
+    AutoLock lock(allocations_lock_);
+    // NB: |allocations_| is an MRU cache, and use of |Get| here updates that
+    // cache.
+    AllocationMap::iterator it = allocations_.Get(discardable);
+    CHECK(it != allocations_.end());
+
+    DCHECK(!it->second.memory);
+    it->second.memory = memory.release();
+  }
+
+  EnforcePolicy();
+}
+
+bool DiscardableMemoryProvider::IsRegisteredForTest(
+    const DiscardableMemory* discardable) {
+  AutoLock lock(allocations_lock_);
+  AllocationMap::iterator it = allocations_.Peek(discardable);
+  return it != allocations_.end();
+}
+
+bool DiscardableMemoryProvider::CanBePurgedForTest(
+    const DiscardableMemory* discardable) {
+  AutoLock lock(allocations_lock_);
+  AllocationMap::iterator it = allocations_.Peek(discardable);
+  return it != allocations_.end() && it->second.memory;
+}
+
+size_t DiscardableMemoryProvider::GetBytesAllocatedForTest() {
+  AutoLock lock(bytes_allocated_lock_);
+  return bytes_allocated_;
+}
+
+void DiscardableMemoryProvider::PurgeLRU(size_t limit) {
+  TRACE_EVENT1("base", "DiscardableMemoryProvider::PurgeLRU", "limit", limit);
+
+  allocations_lock_.AssertAcquired();
+  bytes_allocated_lock_.AssertAcquired();
+
+  for (AllocationMap::reverse_iterator it = allocations_.rbegin();
+       it != allocations_.rend();
+       ++it) {
+    if (bytes_allocated_ <= limit)
+      break;
+    if (!it->second.memory)
+      continue;
+
+    size_t bytes = it->second.bytes;
+    DCHECK_LE(bytes, bytes_allocated_);
+    bytes_allocated_ -= bytes;
+    free(it->second.memory);
+    it->second.memory = NULL;
+  }
+}
+
+void DiscardableMemoryProvider::Purge() {
+  size_t limit = 0;
+  AutoLock bytes_lock(bytes_allocated_lock_);
+  if (bytes_to_reclaim_under_moderate_pressure_ == 0)
+    return;
+
+  if (bytes_to_reclaim_under_moderate_pressure_ < discardable_memory_limit_)
+    limit = bytes_allocated_ - bytes_to_reclaim_under_moderate_pressure_;
+
+  AutoLock lock(allocations_lock_);
+  PurgeLRU(limit);
+}
+
+void DiscardableMemoryProvider::PurgeAll() {
+  AutoLock bytes_lock(bytes_allocated_lock_);
+  AutoLock lock(allocations_lock_);
+  PurgeLRU(0);
+}
+
+void DiscardableMemoryProvider::EnforcePolicy() {
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    if (enforcing_policy_)
+      return;
+  }
+
+  bool exceeded_bound = false;
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    enforcing_policy_ = true;
+    if (discardable_memory_limit_ == 0) {
+      enforcing_policy_ = false;
+      return;
+    }
+    exceeded_bound = bytes_allocated_ > discardable_memory_limit_;
+  }
+
+  if (exceeded_bound)
+    Purge();
+
+  {
+    AutoLock lock(bytes_allocated_lock_);
+    enforcing_policy_ = false;
+  }
+}
+
+}  // namespace internal
+}  // namespace base