Add memory pressure listener to Blob storage

storage/common/blob_storage/blob_storage_constants.h

 // Copyright 2015 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.
 
 #ifndef STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_
 #define STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/callback_forward.h"
 #include "build/build_config.h"
 #include "storage/common/storage_common_export.h"
 
 namespace storage {
 
 constexpr size_t kDefaultIPCMemorySize = 250u * 1024;
 constexpr size_t kDefaultSharedMemorySize = 10u * 1024 * 1024;
 constexpr size_t kDefaultMaxBlobInMemorySpace = 500u * 1024 * 1024;
 constexpr uint64_t kDefaultMaxBlobDiskSpace = 0ull;
 constexpr uint64_t kDefaultMaxPageFileSize = 100ull * 1024 * 1024;
 
 #if defined(OS_ANDROID)
 // On minimal Android maximum in-memory space can be as low as 5MB.
 constexpr uint64_t kDefaultMinPageFileSize = 5ull * 1024 * 1024 / 2;
+const float kDefaultMinPageFileSizeRatioUnderPressure = 0.02;
 #else
 constexpr uint64_t kDefaultMinPageFileSize = 5ull * 1024 * 1024;
+const float kDefaultMinPageFileSizeRatioUnderPressure = 0.002;
 #endif
 
 // All sizes are in bytes.
 struct STORAGE_COMMON_EXPORT BlobStorageLimits {
   // Returns if the current configuration is valid.
   bool IsValid() const;
 
   size_t memory_limit_before_paging() const {
     return max_blob_in_memory_space - min_page_file_size;
   }
@@ skipping 16 matching lines @@
   size_t max_blob_in_memory_space = kDefaultMaxBlobInMemorySpace;
 
   // This is the maximum amount of disk space we can use.
   uint64_t desired_max_disk_space = kDefaultMaxBlobDiskSpace;
   // This value will change based on the amount of free space on the device.
   uint64_t effective_max_disk_space = kDefaultMaxBlobDiskSpace;
 
   // This is the minimum file size we can use when paging blob items to disk.
   // We combine items until we reach at least this size.
   uint64_t min_page_file_size = kDefaultMinPageFileSize;
+  // Ratio of minimum page file size to use to the |max_blob_in_memory_space|,
+  // when under memory pressure (to avoid causing peaks due to file write
+  // buffers).
+  float min_page_file_size_ratio_under_pressure =

[dmurph, 2017/05/10 19:13:34]

Can we put this in terms of the memory limit instead of page size? This and the
constant above.

What about max_blob_in_memory_space_under_pressure_ratio?

Then we can add a comment like so:
"
The ratio applied to max_blob_in_memory_space to reduce memory usage under
memory pressure.
Note: Under pressure we modify the min_page_file_size to ensure we can evict
items until we get below the reduced memory limit.
"

And then kDefaultMaxBlobInMemorySpaceUnderPressureRatio

[ssid, 2017/05/12 01:38:01]

Done.

+      kDefaultMinPageFileSizeRatioUnderPressure;
   // This is the maximum file size we can create.
   uint64_t max_file_size = kDefaultMaxPageFileSize;
 };
 
 enum class IPCBlobItemRequestStrategy {
   UNKNOWN = 0,
   IPC,
   SHARED_MEMORY,
   FILE,
   LAST = FILE
@@ skipping 44 matching lines @@
 
 STORAGE_COMMON_EXPORT bool BlobStatusIsPending(BlobStatus status);
 
 // Returns if the status is a bad enough error to flag the IPC as bad. This is
 // only INVALID_CONSTRUCTION_ARGUMENTS.
 STORAGE_COMMON_EXPORT bool BlobStatusIsBadIPC(BlobStatus status);
 
 }  // namespace storage
 
 #endif  // STORAGE_COMMON_BLOB_STORAGE_BLOB_STORAGE_CONSTANTS_H_