[BlobStorage] Enabling disk paging and direct storage.

storage/common/blob_storage/blob_storage_constants.h

Index: storage/common/blob_storage/blob_storage_constants.h
diff --git a/storage/common/blob_storage/blob_storage_constants.h b/storage/common/blob_storage/blob_storage_constants.h
index b94e886f3de7bc9685442035789a2833dac6ed64..cfe9c563d0570c93b040308c8969ffb9b2b00dcd 100644
--- a/storage/common/blob_storage/blob_storage_constants.h
+++ b/storage/common/blob_storage/blob_storage_constants.h
@@ -13,29 +13,49 @@
 
 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 kDefaultMinPageFileSize = 5ull * 1024 * 1024;
+constexpr uint64_t kDefaultMaxPageFileSize = 100ull * 1024 * 1024;
+
 // All sizes are in bytes.
-struct BlobStorageLimits {
+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;
   }
 
+  // If disk space goes less than this we stop allocating more disk quota.
+  uint64_t min_available_disk_space() const {

[Mark P, 2017/01/10 23:57:00]

As someone reviewing code that uses this struct, I find the variable / function
names confusing, especially min_available_disk_space and desired_max_disk_space.

I read these originally as the minimum available disk space that the blog system
needs and the desired maximum disk space the blob system needs.

If I read the comments within this struct (which it took me a while to do,
because I thought my interpretation was obvious based on the names), the
difference is clear.  The former refers to min available *outside the blob
system* and the latter refers to *within the blob system*.

Take this or leave it.  You may want to revise these to prevent confusing from
future engineers.

[dmurph, 2017/01/11 01:49:22]

I changed this to |min_available_external_disk_space()|

+    return 2ull * memory_limit_before_paging();
+  }
+
+  bool IsDiskSpaceConstrained() const {
+    return desired_max_disk_space != effective_max_disk_space;
+  }
+
   // This is the maximum amount of memory we can send in an IPC.
-  size_t max_ipc_memory_size = 250 * 1024;
+  size_t max_ipc_memory_size = kDefaultIPCMemorySize;
   // This is the maximum size of a shared memory handle.
-  size_t max_shared_memory_size = 10 * 1024 * 1024;
+  size_t max_shared_memory_size = kDefaultSharedMemorySize;
 
   // This is the maximum amount of memory we can use to store blobs.
-  size_t max_blob_in_memory_space = 500 * 1024 * 1024;
+  size_t max_blob_in_memory_space = kDefaultMaxBlobInMemorySpace;
 
   // This is the maximum amount of disk space we can use.
-  // TODO(dmurph): Determine initial heuristic based on disk usage & arch.
-  uint64_t max_blob_disk_space = 0ull;
+  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 = 5 * 1024 * 1024;
+  uint64_t min_page_file_size = kDefaultMinPageFileSize;
   // This is the maximum file size we can create.
-  uint64_t max_file_size = 100 * 1024 * 1024;
+  uint64_t max_file_size = kDefaultMaxPageFileSize;
 };
 
 enum class IPCBlobItemRequestStrategy {