[BlobStorage] BlobMemoryController & tests

storage/browser/blob/blob_memory_controller.cc

+// Copyright 2016 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 "storage/browser/blob/blob_memory_controller.h"
+
+#include <algorithm>
+
+#include "base/callback.h"
+#include "base/callback_helpers.h"
+#include "base/containers/small_map.h"
+#include "base/files/file_util.h"
+#include "base/location.h"
+#include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/numerics/safe_conversions.h"
+#include "base/numerics/safe_math.h"
+#include "base/single_thread_task_runner.h"
+#include "base/single_thread_task_runner.h"
+#include "base/stl_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/task_runner.h"
+#include "base/task_runner_util.h"
+#include "base/time/time.h"
+#include "base/trace_event/trace_event.h"
+#include "base/tuple.h"
+#include "storage/browser/blob/blob_data_builder.h"
+#include "storage/browser/blob/blob_data_item.h"
+#include "storage/browser/blob/shareable_blob_data_item.h"
+#include "storage/browser/blob/shareable_file_reference.h"
+#include "storage/common/data_element.h"
+
+using base::File;
+using base::FilePath;
+using FileCreationInfo = storage::BlobMemoryController::FileCreationInfo;
+
+namespace storage {
+namespace {
+using PendingMemoryQuotaRequest =
+    BlobMemoryController::PendingMemoryQuotaRequest;
+using PendingFileQuotaRequest = BlobMemoryController::PendingFileQuotaRequest;
+
+// Creates a file in the given directory w/ the given filename and size.
+std::vector<BlobMemoryController::FileCreationInfo> CreateFiles(
+    std::vector<scoped_refptr<ShareableFileReference>> file_references) {
+  std::vector<BlobMemoryController::FileCreationInfo> result;
+
+  for (scoped_refptr<ShareableFileReference>& file_ref : file_references) {
+    result.push_back(BlobMemoryController::FileCreationInfo());
+    BlobMemoryController::FileCreationInfo& creation_info = result.back();
+    // Try to open our file.
+    File file(file_ref->path(), File::FLAG_CREATE_ALWAYS | File::FLAG_WRITE);
+    creation_info.file_reference = std::move(file_ref);
+    creation_info.error = file.error_details();
+    UMA_HISTOGRAM_ENUMERATION("Storage.Blob.TransportFileCreate",
+                              -creation_info.error, -File::FILE_ERROR_MAX);
+    if (creation_info.error != File::FILE_OK)
+      return std::vector<BlobMemoryController::FileCreationInfo>();
+
+    // Grab the file info to get the "last modified" time and store the file.
+    File::Info file_info;
+    bool success = file.GetInfo(&file_info);
+    UMA_HISTOGRAM_BOOLEAN("Storage.Blob.TransportFileInfoSuccess", success);
+    creation_info.error = success ? File::FILE_OK : File::FILE_ERROR_FAILED;
+    if (!success)
+      return std::vector<BlobMemoryController::FileCreationInfo>();
+    creation_info.file = std::move(file);
+  }
+  return result;
+}
+
+BlobMemoryController::FileCreationInfo WriteItemsToFile(
+    std::vector<scoped_refptr<ShareableBlobDataItem>>* items,
+    size_t total_size_bytes,
+    scoped_refptr<ShareableFileReference> file_reference) {
+  DCHECK_NE(0u, total_size_bytes);
+  UMA_HISTOGRAM_MEMORY_KB("Storage.Blob.PageFileSize", total_size_bytes / 1024);
+
+  // Create our file.
+  BlobMemoryController::FileCreationInfo creation_info;
+  File file(file_reference->path(),
+            File::FLAG_CREATE_ALWAYS | File::FLAG_WRITE);
+  creation_info.file_reference = std::move(file_reference);
+  creation_info.error = file.error_details();
+  UMA_HISTOGRAM_ENUMERATION("Storage.Blob.PageFileCreate", -creation_info.error,
+                            -File::FILE_ERROR_MAX);
+  if (creation_info.error != File::FILE_OK)
+    return creation_info;
+
+  // Write data.
+  file.SetLength(total_size_bytes);
+  int bytes_written = 0;
+  for (const auto& refptr : *items) {
+    const DataElement& element = refptr->item()->data_element();
+    DCHECK_EQ(DataElement::TYPE_BYTES, element.type());
+    size_t length = base::checked_cast<size_t>(element.length());
+    size_t bytes_left = length;
+    while (bytes_left > 0) {
+      bytes_written =
+          file.WriteAtCurrentPos(element.bytes() + (length - bytes_left),
+                                 base::saturated_cast<int>(bytes_left));
+      if (bytes_written < 0)
+        break;
+      DCHECK_LE(static_cast<size_t>(bytes_written), bytes_left);
+      bytes_left -= bytes_written;
+    }
+    if (bytes_written < 0)
+      break;
+  }
+  UMA_HISTOGRAM_BOOLEAN("Storage.Blob.PageFileWriteSuccess", bytes_written > 0);
+
+  // Grab our modification time and create our SharedFileReference to manage the
+  // lifetime of the file.
+  File::Info info;
+  bool success = file.GetInfo(&info);
+  UMA_HISTOGRAM_BOOLEAN("Storage.Blob.PageFileInfoSuccess", success);
+  creation_info.error =
+      bytes_written < 0 || !success ? File::FILE_ERROR_FAILED : File::FILE_OK;
+  creation_info.last_modified = info.last_modified;
+  return creation_info;
+}
+
+// Here so we can destruct files on the correct thread if the user cancels.
+void DestructFiles(std::vector<BlobMemoryController::FileCreationInfo> files) {}
+
+std::vector<scoped_refptr<ShareableBlobDataItem>> WrapInRefPtrs(
+    const std::vector<ShareableBlobDataItem*> items_ptrs) {
+  std::vector<scoped_refptr<ShareableBlobDataItem>> result;
+  for (ShareableBlobDataItem* item : items_ptrs) {
+    result.push_back(make_scoped_refptr(item));
+  }
+  return result;
+}
+
+}  // namespace
+
+BlobMemoryController::FileCreationInfo::FileCreationInfo() = default;
+BlobMemoryController::FileCreationInfo::~FileCreationInfo() = default;
+FileCreationInfo::FileCreationInfo(FileCreationInfo&&) = default;
+FileCreationInfo& FileCreationInfo::operator=(FileCreationInfo&&) = default;
+
+PendingMemoryQuotaRequest BlobMemoryController::GetInvalidMemoryQuotaRequest() {
+  return blobs_waiting_for_paging_.end();
+}
+
+BlobMemoryController::BlobMemoryController()
+    : recent_item_cache_(
+          base::MRUCache<uint64_t, ShareableBlobDataItem*>::NO_AUTO_EVICT),
+      ptr_factory_(this) {}
+
+BlobMemoryController::~BlobMemoryController() {}
+
+void BlobMemoryController::EnableFilePaging(
+    const base::FilePath& storage_directory,
+    scoped_refptr<base::TaskRunner> file_runner) {
+  DCHECK(!storage_directory.empty());
+  file_runner_ = std::move(file_runner);
+  blob_storage_dir_ = storage_directory;
+  file_paging_enabled_ = true;
+}
+
+void BlobMemoryController::DisableFilePaging() {
+  file_paging_enabled_ = false;
+  blob_memory_used_ += in_flight_memory_used_;
+  in_flight_memory_used_ = 0;
+  pending_file_request_sizes_.clear();
+  items_saving_to_disk_.clear();
+  for (const auto& size_callback_pair : blobs_waiting_for_paging_)
+    size_callback_pair.second.Run(false);
+  pending_pagings_ = 0;
+  blobs_waiting_for_paging_.clear();
+  blobs_waiting_for_paging_size_ = 0;
+  recent_item_cache_.Clear();
+  recent_item_cache_bytes_ = 0;
+  RecordTracingCounters();
+}
+
+BlobMemoryController::Strategy BlobMemoryController::DetermineStrategy(
+    size_t preemptive_transported_bytes,
+    uint64_t total_transportation_bytes) const {
+  if (total_transportation_bytes == 0) {
+    return Strategy::NONE_NEEDED;
+  }
+  if (!CanReserveQuota(total_transportation_bytes)) {
+    return Strategy::TOO_LARGE;
+  }
+  // Handle the case where we have all the bytes preemptively transported, and
+  // we can also fit them.
+  if (preemptive_transported_bytes == total_transportation_bytes &&
+      blobs_waiting_for_paging_.empty() &&
+      preemptive_transported_bytes < GetAvailableMemoryForBlobs()) {
+    return Strategy::NONE_NEEDED;
+  }
+  if (file_paging_enabled_ &&
+      (total_transportation_bytes > limits_.max_blob_in_memory_space)) {
+    return Strategy::FILE;
+  }
+  if (total_transportation_bytes > limits_.max_ipc_memory_size) {
+    return Strategy::SHARED_MEMORY;
+  }
+  return Strategy::IPC;
+}
+
+bool BlobMemoryController::CanReserveQuota(uint64_t size) const {
+  // We check each size independently as a blob can't be constructed in both
+  // disk and memory.
+  return size <= GetAvailableMemoryForBlobs() ||
+         size <= GetAvailableFileSpaceForBlobs();
+}
+
+PendingMemoryQuotaRequest BlobMemoryController::ReserveMemoryQuota(
+    std::vector<ShareableBlobDataItem*> unreserved_memory_items,
+    const MemoryQuotaRequestCallback& success_callback) {
+  uint64_t total_bytes_needed = 0;
+  for (ShareableBlobDataItem* item : unreserved_memory_items) {
+    DCHECK_EQ(ShareableBlobDataItem::QUOTA_NEEDED, item->state());
+    DCHECK(item->item()->type() == DataElement::TYPE_BYTES_DESCRIPTION ||
+           item->item()->type() == DataElement::TYPE_BYTES);
+    total_bytes_needed += item->item()->length();
+    item->state_ = ShareableBlobDataItem::QUOTA_REQUESTED;
+  }
+
+  if (total_bytes_needed == 0) {
+    success_callback.Run(true);
+    return blobs_waiting_for_paging_.end();
+  }
+
+  if (!file_paging_enabled_) {
+    blob_memory_used_ += total_bytes_needed;
+    for (ShareableBlobDataItem* item : unreserved_memory_items) {
+      item->state_ = ShareableBlobDataItem::QUOTA_GRANTED;
+    }
+    success_callback.Run(true);
+    return blobs_waiting_for_paging_.end();
+  }
+
+  // If we're currently waiting for blobs to page already, then we add
+  // ourselves to the end of the queue. Once paging is complete, we'll schedule
+  // more paging for any more pending blobs.
+  if (!blobs_waiting_for_paging_.empty()) {
+    std::vector<scoped_refptr<ShareableBlobDataItem>> item_handles =
+        WrapInRefPtrs(unreserved_memory_items);
+    blobs_waiting_for_paging_.push_back(std::make_pair(
+        total_bytes_needed,
+        base::Bind(&BlobMemoryController::SetStateQuotaGrantedAndCallback,
+                   ptr_factory_.GetWeakPtr(), base::Passed(&item_handles),
+                   success_callback)));
+    blobs_waiting_for_paging_size_ += total_bytes_needed;
+    return --blobs_waiting_for_paging_.end();
+  }
+
+  // Store right away if we can.
+  if (total_bytes_needed <= GetAvailableMemoryForBlobs()) {
+    // If we're past our blob memory limit, then schedule our paging.
+    blob_memory_used_ += total_bytes_needed;
+    for (ShareableBlobDataItem* item : unreserved_memory_items) {
+      item->state_ = ShareableBlobDataItem::QUOTA_GRANTED;
+    }
+    MaybeSchedulePagingUntilSystemHealthy();
+    success_callback.Run(true);
+    return blobs_waiting_for_paging_.end();
+  }
+
+  // This means we're too big for memory.
+  DCHECK(blobs_waiting_for_paging_.empty());
+  DCHECK_EQ(0u, blobs_waiting_for_paging_size_);
+  std::vector<scoped_refptr<ShareableBlobDataItem>> item_handles =
+      WrapInRefPtrs(unreserved_memory_items);
+  blobs_waiting_for_paging_.push_back(std::make_pair(
+      total_bytes_needed,
+      base::Bind(&BlobMemoryController::SetStateQuotaGrantedAndCallback,
+                 ptr_factory_.GetWeakPtr(), base::Passed(&item_handles),
+                 success_callback)));
+  blobs_waiting_for_paging_size_ = total_bytes_needed;
+  auto it = --blobs_waiting_for_paging_.end();
+  MaybeSchedulePagingUntilSystemHealthy();
+  return it;
+}
+
+void BlobMemoryController::CancelMemoryQuotaReservation(
+    const PendingMemoryQuotaRequest& request) {
+  if (request == blobs_waiting_for_paging_.end())
+    return;
+  blobs_waiting_for_paging_size_ -= request->first;
+  blobs_waiting_for_paging_.erase(request);
+  return;
+}
+
+PendingFileQuotaRequest BlobMemoryController::ReserveFileQuota(
+    std::vector<ShareableBlobDataItem*> unreserved_file_items,
+    const FileQuotaRequestCallback& success_callback) {
+  uint64_t total_files_size_needed = 0;
+  base::SmallMap<std::map<uint64_t, uint64_t>> file_sizes;
+  std::vector<scoped_refptr<ShareableBlobDataItem>> item_handles;
+  for (ShareableBlobDataItem* item : unreserved_file_items) {
+    DCHECK_EQ(ShareableBlobDataItem::QUOTA_NEEDED, item->state());
+    DCHECK_EQ(DataElement::TYPE_FILE, item->item()->type());
+
+    const DataElement& element = item->item()->data_element();
+    DCHECK(BlobDataBuilder::IsFutureFileItem(element));
+
+    uint64_t file_id = BlobDataBuilder::GetFutureFileID(element);
+    auto it = file_sizes.find(file_id);
+    if (it != file_sizes.end()) {
+      it->second = std::max(it->second, element.offset() + element.length());
+    } else {
+      file_sizes[file_id] = element.offset() + element.length();
+    }
+    total_files_size_needed += element.length();
+    item->state_ = ShareableBlobDataItem::QUOTA_REQUESTED;
+    item_handles.push_back(make_scoped_refptr(item));
+  }
+
+  DCHECK_LE(total_files_size_needed, GetAvailableFileSpaceForBlobs());
+  disk_used_ += total_files_size_needed;
+  std::vector<scoped_refptr<ShareableFileReference>> file_refs;
+  std::vector<uint64_t> sizes;
+  for (const auto& size_pair : file_sizes) {
+    std::string file_name = base::Uint64ToString(current_file_num_++);
+    file_refs.push_back(ShareableFileReference::GetOrCreate(
+        blob_storage_dir_.Append(file_name),
+        ShareableFileReference::DELETE_ON_FINAL_RELEASE, file_runner_.get()));
+    sizes.push_back(size_pair.second);
+  }
+
+  uint64_t disk_quota_entry = ++curr_disk_save_entry_;
+  if (disk_quota_entry == kInvalidFileQuotaRequest) {
+    disk_quota_entry = ++curr_disk_save_entry_;
+  }
+  pending_file_request_sizes_[disk_quota_entry] = total_files_size_needed;
+  base::PostTaskAndReplyWithResult(
+      file_runner_.get(), FROM_HERE,
+      base::Bind(&CreateFiles, base::Passed(&file_refs)),
+      base::Bind(&BlobMemoryController::OnCreateFiles,
+                 ptr_factory_.GetWeakPtr(), base::Passed(&sizes),
+                 base::Passed(&item_handles), disk_quota_entry,
+                 success_callback));
+  RecordTracingCounters();
+  return disk_quota_entry;
+}
+
+void BlobMemoryController::CancelFileQuotaReservation(
+    const PendingFileQuotaRequest& entry) {
+  auto it = pending_file_request_sizes_.find(entry);
+  if (it == pending_file_request_sizes_.end())
+    return;
+  disk_used_ -= it->second;
+  pending_file_request_sizes_.erase(it);
+}
+
+void BlobMemoryController::MaybeFreeQuotaForItems(
+    const std::vector<scoped_refptr<ShareableBlobDataItem>>& items) {
+  uint64_t total_memory_freeing = 0;
+  std::unordered_set<uint64_t> visited_items;
+  for (const scoped_refptr<ShareableBlobDataItem>& item : items) {
+    switch (item->state()) {
+      case ShareableBlobDataItem::QUOTA_NEEDED:
+      case ShareableBlobDataItem::QUOTA_REQUESTED:
+      case ShareableBlobDataItem::POPULATED_WITHOUT_QUOTA:
+        continue;
+      case ShareableBlobDataItem::QUOTA_GRANTED:
+      case ShareableBlobDataItem::POPULATED_WITH_QUOTA:
+        break;
+    }
+    // We only care about bytes items that don't have blobs referencing them,
+    // and we remove duplicates.
+    DataElement::Type type = item->item()->type();
+    if (!item->referencing_blobs().empty() ||
+        (type != DataElement::TYPE_BYTES &&
+         type != DataElement::TYPE_BYTES_DESCRIPTION) ||
+        base::ContainsKey(visited_items, item->item_id()))
+      continue;
+    visited_items.insert(item->item_id());

[pwnall, 2016/09/21 22:56:58]

Do these items need to be released somehow?

Granted I still haven't put all the pieces together, I'm having a bit of trouble
understanding why it's OK to simply count the memory as freed here.

[dmurph, 2016/09/23 20:15:13]

Not here, this class doesn't manage the lifetime of those objects, just the
quota for the memory they contain.

+    total_memory_freeing += item->item()->length();

[pwnall, 2016/09/21 22:56:58]

memory_to_be_freed?

[dmurph, 2016/09/23 20:15:14]

Done.

+  }
+  if (total_memory_freeing != 0) {
+    DCHECK_GE(blob_memory_used_, total_memory_freeing);
+    blob_memory_used_ -= total_memory_freeing;
+    MaybeGrantPendingQuotaRequests();
+  }
+}
+
+void BlobMemoryController::FreeQuotaForPagedItemReference(
+    const scoped_refptr<ShareableBlobDataItem>& item) {
+  CHECK_EQ(item->state(), ShareableBlobDataItem::QUOTA_GRANTED);
+  CHECK_EQ(item->item()->type(), DataElement::TYPE_BYTES_DESCRIPTION);
+  blob_memory_used_ -= item->item()->length();
+  MaybeGrantPendingQuotaRequests();
+}
+
+void BlobMemoryController::UpdateBlobItemInRecents(
+    ShareableBlobDataItem* item) {
+  DCHECK_EQ(DataElement::TYPE_BYTES, item->item()->type());
+  DCHECK_EQ(ShareableBlobDataItem::POPULATED_WITH_QUOTA, item->state());
+  // We don't want to re-add the item if we're currently paging it to disk.
+  if (items_saving_to_disk_.find(item->item_id()) !=
+      items_saving_to_disk_.end())
+    return;
+  auto iterator = recent_item_cache_.Get(item->item_id());
+  if (iterator == recent_item_cache_.end()) {
+    recent_item_cache_bytes_ += static_cast<size_t>(item->item()->length());
+    recent_item_cache_.Put(item->item_id(), item);
+    MaybeSchedulePagingUntilSystemHealthy();
+  }
+}
+
+void BlobMemoryController::RemoveBlobItemInRecents(
+    const ShareableBlobDataItem& item) {
+  auto iterator = recent_item_cache_.Get(item.item_id());
+  if (iterator != recent_item_cache_.end()) {
+    size_t size = static_cast<size_t>(item.item()->length());
+    DCHECK_GE(recent_item_cache_bytes_, size);
+    recent_item_cache_bytes_ -= size;
+    recent_item_cache_.Erase(iterator);
+  }
+}
+
+void BlobMemoryController::SetStateQuotaGrantedAndCallback(
+    std::vector<scoped_refptr<ShareableBlobDataItem>> items,
+    const MemoryQuotaRequestCallback& final_callback,
+    bool success) {
+  if (!success) {
+    final_callback.Run(false);
+    return;
+  }
+  for (const auto& item : items) {
+    item->state_ = ShareableBlobDataItem::QUOTA_GRANTED;
+  }
+  final_callback.Run(true);
+  return;
+}
+
+void BlobMemoryController::OnCreateFiles(
+    std::vector<uint64_t> file_sizes,
+    std::vector<scoped_refptr<ShareableBlobDataItem>> pending_items,
+    uint64_t disk_quota_entry,
+    const FileQuotaRequestCallback& file_callback,
+    std::vector<FileCreationInfo> result) {
+  if (result.empty()) {
+    for (uint64_t size : file_sizes) {
+      disk_used_ -= size;
+    }
+    file_callback.Run(false, std::vector<FileCreationInfo>());
+    DisableFilePaging();
+    return;
+  }
+  // Check if the user cancelled the file request.
+  if (pending_file_request_sizes_.erase(disk_quota_entry) == 0) {
+    file_runner_->PostTask(FROM_HERE,
+                           base::Bind(&DestructFiles, base::Passed(&result)));
+    return;
+  }
+  DCHECK_EQ(file_sizes.size(), result.size());
+  for (size_t i = 0; i < result.size(); i++) {
+    result[i].file_reference->AddFinalReleaseCallback(
+        base::Bind(&BlobMemoryController::OnBlobFileDelete,
+                   ptr_factory_.GetWeakPtr(), file_sizes[i]));
+  }
+  for (const auto& item : pending_items) {
+    item->state_ = ShareableBlobDataItem::QUOTA_GRANTED;
+  }
+  file_callback.Run(true, std::move(result));
+}
+
+void BlobMemoryController::MaybeGrantPendingQuotaRequests() {
+  size_t space_available = limits_.max_blob_in_memory_space - blob_memory_used_;
+  while (!blobs_waiting_for_paging_.empty() &&
+         limits_.max_blob_in_memory_space - blob_memory_used_ >=
+             blobs_waiting_for_paging_.front().first) {
+    auto size_callback_pair = blobs_waiting_for_paging_.front();
+    blobs_waiting_for_paging_.pop_front();
+    space_available -= size_callback_pair.first;
+    blobs_waiting_for_paging_size_ -= size_callback_pair.first;
+    blob_memory_used_ += size_callback_pair.first;
+    size_callback_pair.second.Run(true);
+  }
+  RecordTracingCounters();
+}
+
+void BlobMemoryController::MaybeSchedulePagingUntilSystemHealthy() {
+  // Don't do paging when others are happening, as we don't change our
+  // blobs_waiting_for_paging_size_ value until after the paging files have
+  // been written.
+  if (pending_pagings_ != 0 || !file_paging_enabled_)
+    return;
+
+  // We try to page items to disk until our current system size + requested
+  // memory is below our size limit.
+  while (blobs_waiting_for_paging_size_ + blob_memory_used_ >
+         limits_.max_blob_in_memory_space) {
+    // We only page when we have enough items to fill a while page file.
+    if (recent_item_cache_bytes_ < limits_.min_page_file_size)
+      break;
+    DCHECK_LE(limits_.min_page_file_size,
+              static_cast<uint64_t>(blob_memory_used_));
+    size_t total_items_size = 0;
+    std::unique_ptr<std::vector<scoped_refptr<ShareableBlobDataItem>>>
+        items_for_disk(new std::vector<scoped_refptr<ShareableBlobDataItem>>());
+    // Collect our items.
+    while (total_items_size < limits_.min_page_file_size &&
+           !recent_item_cache_.empty()) {
+      auto iterator = --recent_item_cache_.end();
+      ShareableBlobDataItem* item = iterator->second;
+      DCHECK(item);
+      DCHECK_EQ(item->item()->type(), DataElement::TYPE_BYTES);
+      recent_item_cache_.Erase(iterator);
+      recent_item_cache_bytes_ -= static_cast<size_t>(item->item()->length());
+      items_saving_to_disk_.insert(item->item_id());
+      size_t size = base::checked_cast<size_t>(item->item()->length());
+      total_items_size += size;
+      items_for_disk->push_back(make_scoped_refptr(item));
+    }
+    if (total_items_size == 0)
+      break;
+
+    // Update our bookkeeping.
+    pending_pagings_++;
+    disk_used_ += total_items_size;
+    DCHECK_GE(blob_memory_used_, total_items_size);
+    blob_memory_used_ -= total_items_size;
+    in_flight_memory_used_ += total_items_size;
+    std::string file_name = base::Uint64ToString(current_file_num_++);
+    // Create our file reference.
+    scoped_refptr<ShareableFileReference> file_ref =
+        ShareableFileReference::GetOrCreate(
+            blob_storage_dir_.Append(file_name),
+            ShareableFileReference::DELETE_ON_FINAL_RELEASE,
+            file_runner_.get());
+    // Add the release callback so we decrement our disk usage on file deletion.
+    file_ref->AddFinalReleaseCallback(
+        base::Bind(&BlobMemoryController::OnBlobFileDelete,
+                   ptr_factory_.GetWeakPtr(), total_items_size));
+    // Post the file writing task.
+    base::PostTaskAndReplyWithResult(
+        file_runner_.get(), FROM_HERE,
+        base::Bind(&WriteItemsToFile, items_for_disk.get(), total_items_size,
+                   base::Passed(&file_ref)),
+        base::Bind(&BlobMemoryController::OnPagingComplete,
+                   ptr_factory_.GetWeakPtr(), base::Passed(&items_for_disk),
+                   total_items_size));
+  }
+  RecordTracingCounters();
+}
+
+void BlobMemoryController::OnPagingComplete(
+    std::unique_ptr<std::vector<scoped_refptr<ShareableBlobDataItem>>> items,
+    size_t total_items_size,
+    FileCreationInfo result) {
+  if (!file_paging_enabled_)
+    return;
+  if (result.error != File::FILE_OK) {
+    UMA_HISTOGRAM_ENUMERATION("Storage.Blob.PagingError", -result.error,
+                              -File::FILE_ERROR_MAX);
+    disk_used_ -= total_items_size;
+    DisableFilePaging();
+    return;
+  }
+  DCHECK_LT(0u, pending_pagings_);
+  pending_pagings_--;
+
+  // Switch from the data backing item to a new file backing item.
+  uint64_t offset = 0;
+  for (const scoped_refptr<ShareableBlobDataItem>& shareable_item :
+       *items.get()) {
+    scoped_refptr<BlobDataItem> new_item(new BlobDataItem(
+        base::WrapUnique(new DataElement()), result.file_reference));
+    new_item->data_element_ptr()->SetToFilePathRange(
+        result.file_reference->path(), offset, shareable_item->item()->length(),
+        result.last_modified);
+    shareable_item->item_ = new_item;
+    items_saving_to_disk_.erase(shareable_item->item_id());
+    offset += shareable_item->item()->length();
+  }
+  in_flight_memory_used_ -= total_items_size;
+
+  // We want callback on blobs up to the amount we've freed.
+  MaybeGrantPendingQuotaRequests();
+
+  // If we still have more blobs waiting and we're not waiting on more paging
+  // operations, schedule more.
+  MaybeSchedulePagingUntilSystemHealthy();
+}
+
+void BlobMemoryController::RecordTracingCounters() {
+  TRACE_COUNTER2("Blob", "MemoryUsage", "RegularStorage", blob_memory_used_,
+                 "InFlightToDisk", in_flight_memory_used_);
+  TRACE_COUNTER1("Blob", "DiskUsage", disk_used_);
+  TRACE_COUNTER1("Blob", "TranfersPendingOnDisk",
+                 blobs_waiting_for_paging_.size());
+  TRACE_COUNTER1("Blob", "TranfersBytesPendingOnDisk",
+                 blobs_waiting_for_paging_size_);
+}
+
+size_t BlobMemoryController::GetAvailableMemoryForBlobs() const {
+  if (limits_.total_memory_space() < memory_usage())
+    return 0;
+  return limits_.total_memory_space() - memory_usage();
+}
+
+uint64_t BlobMemoryController::GetAvailableFileSpaceForBlobs() const {
+  if (!file_paging_enabled_)
+    return 0;
+  return limits_.max_blob_disk_space - disk_used_ -
+         blobs_waiting_for_paging_size_;
+}
+
+void BlobMemoryController::OnBlobFileDelete(uint64_t size,
+                                            const base::FilePath& path) {
+  DCHECK_LE(size, disk_used_);
+  disk_used_ -= size;
+}
+
+}  // namespace storage