diff --git a/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java b/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
index b958c28..f844cc1 100644
--- a/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
+++ b/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
@@ -17,6 +17,7 @@
 package com.android.externalstorage;
 
 import android.annotation.Nullable;
+import android.app.usage.StorageStatsManager;
 import android.content.ContentResolver;
 import android.content.Context;
 import android.content.UriPermission;
@@ -49,10 +50,12 @@
 import java.io.File;
 import java.io.FileDescriptor;
 import java.io.FileNotFoundException;
+import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
+import java.util.UUID;
 
 public class ExternalStorageProvider extends FileSystemProvider {
     private static final String TAG = "ExternalStorage";
@@ -79,6 +82,7 @@
     private static class RootInfo {
         public String rootId;
         public String volumeId;
+        public UUID storageUuid;
         public int flags;
         public String title;
         public String docId;
@@ -124,6 +128,7 @@
 
             final String rootId;
             final String title;
+            final UUID storageUuid;
             if (volume.getType() == VolumeInfo.TYPE_EMULATED) {
                 // We currently only support a single emulated volume mounted at
                 // a time, and it's always considered the primary
@@ -142,17 +147,20 @@
                     title = !TextUtils.isEmpty(deviceName)
                             ? deviceName
                             : getContext().getString(R.string.root_internal_storage);
+                    storageUuid = StorageManager.UUID_DEFAULT;
                 } else {
                     // This should cover all other storage devices, like an SD card
                     // or USB OTG drive plugged in. Using getBestVolumeDescription()
                     // will give us a nice string like "Samsung SD card" or "SanDisk USB drive"
                     final VolumeInfo privateVol = mStorageManager.findPrivateForEmulated(volume);
                     title = mStorageManager.getBestVolumeDescription(privateVol);
+                    storageUuid = StorageManager.convert(privateVol.fsUuid);
                 }
             } else if (volume.getType() == VolumeInfo.TYPE_PUBLIC
                     && volume.getMountUserId() == userId) {
                 rootId = volume.getFsUuid();
                 title = mStorageManager.getBestVolumeDescription(volume);
+                storageUuid = null;
             } else {
                 // Unsupported volume; ignore
                 continue;
@@ -172,6 +180,7 @@
 
             root.rootId = rootId;
             root.volumeId = volume.id;
+            root.storageUuid = storageUuid;
             root.flags = Root.FLAG_LOCAL_ONLY
                     | Root.FLAG_SUPPORTS_SEARCH
                     | Root.FLAG_SUPPORTS_IS_CHILD;
@@ -385,8 +394,22 @@
                 row.add(Root.COLUMN_FLAGS, root.flags);
                 row.add(Root.COLUMN_TITLE, root.title);
                 row.add(Root.COLUMN_DOCUMENT_ID, root.docId);
-                row.add(Root.COLUMN_AVAILABLE_BYTES,
-                        root.reportAvailableBytes ? root.path.getUsableSpace() : -1);
+
+                long availableBytes = -1;
+                if (root.reportAvailableBytes) {
+                    if (root.storageUuid != null) {
+                        try {
+                            availableBytes = getContext()
+                                    .getSystemService(StorageStatsManager.class)
+                                    .getFreeBytes(root.storageUuid);
+                        } catch (IOException e) {
+                            Log.w(TAG, e);
+                        }
+                    } else {
+                        availableBytes = root.path.getUsableSpace();
+                    }
+                }
+                row.add(Root.COLUMN_AVAILABLE_BYTES, availableBytes);
             }
         }
         return result;
diff --git a/services/usage/java/com/android/server/usage/StorageStatsService.java b/services/usage/java/com/android/server/usage/StorageStatsService.java
index dae74db..16b73d5 100644
--- a/services/usage/java/com/android/server/usage/StorageStatsService.java
+++ b/services/usage/java/com/android/server/usage/StorageStatsService.java
@@ -31,6 +31,7 @@
 import android.content.pm.PackageStats;
 import android.content.pm.UserInfo;
 import android.net.TrafficStats;
+import android.net.Uri;
 import android.os.Binder;
 import android.os.Environment;
 import android.os.FileUtils;
@@ -467,6 +468,7 @@
                     if (bytesDelta > mMinimumThresholdBytes) {
                         mPreviousBytes = mStats.getAvailableBytes();
                         recalculateQuotas(getInitializedStrategy());
+                        notifySignificantDelta();
                     }
                     sendEmptyMessageDelayed(MSG_CHECK_STORAGE_DELTA, DELAY_IN_MILLIS);
                     break;
@@ -518,4 +520,13 @@
         return Settings.Global.getInt(
                 resolver, Settings.Global.ENABLE_CACHE_QUOTA_CALCULATION, 1) != 0;
     }
+
+    /**
+     * Hacky way of notifying that disk space has changed significantly; we do
+     * this to cause "available space" values to be requeried.
+     */
+    void notifySignificantDelta() {
+        mContext.getContentResolver().notifyChange(
+                Uri.parse("content://com.android.externalstorage.documents/"), null, false);
+    }
 }