【Android 性能引擎】文件碎片

整理碎片，提升整机性能。

入口：

PMS#performFstrimIfNeeded

public void performFstrimIfNeeded() {
        PackageManagerServiceUtils.enforceSystemOrRoot("Only the system can request fstrim");

        // Before everything else, see whether we need to fstrim.
        try {
            IStorageManager sm = InstallLocationUtils.getStorageManager();
            if (sm != null) {
                boolean doTrim = false;
                final long interval = android.provider.Settings.Global.getLong(
                        mContext.getContentResolver(),
                        android.provider.Settings.Global.FSTRIM_MANDATORY_INTERVAL,
                        DEFAULT_MANDATORY_FSTRIM_INTERVAL);
                if (interval > 0) {
                    final long timeSinceLast = System.currentTimeMillis() - sm.lastMaintenance();
                    if (timeSinceLast > interval) {
                        doTrim = true;
                        Slog.w(TAG, "No disk maintenance in " + timeSinceLast
                                + "; running immediately");
                    }
                }
                if (doTrim) {
                    if (!isFirstBoot()) {
                        if (mDexOptHelper.isDexOptDialogShown()) {
                            try {
                                ActivityManager.getService().showBootMessage(
                                        mContext.getResources().getString(
                                                R.string.android_upgrading_fstrim), true);
                            } catch (RemoteException e) {
                            }
                        }
                    }
                    sm.runMaintenance();
                }
            } else {
                Slog.e(TAG, "storageManager service unavailable!");
            }
        } catch (RemoteException e) {
            // Can't happen; StorageManagerService is local
        }
    }

StorageManagerService#runIdleMaint

void runIdleMaint(Runnable callback) {
        enforcePermission(android.Manifest.permission.MOUNT_FORMAT_FILESYSTEMS);
        try {
            // Block based checkpoint process runs fstrim. So, if checkpoint is in progress
            // (first boot after OTA), We skip idle maintenance and make sure the last
            // fstrim time is still updated. If file based checkpoints are used, we run
            // idle maintenance (GC + fstrim) regardless of checkpoint status.
            if (!needsCheckpoint() || !supportsBlockCheckpoint()) {
                mVold.runIdleMaint(mNeedGC, new IVoldTaskListener.Stub() {
                    @Override
                    public void onStatus(int status, PersistableBundle extras) {
                        // Not currently used
                    }
                    @Override
                    public void onFinished(int status, PersistableBundle extras) {
                        if (callback != null) {
                            BackgroundThread.getHandler().post(callback);
                        }
                    }
                });
            } else {
                Slog.i(TAG, "Skipping idle maintenance - block based checkpoint in progress");
            }
        } catch (Exception e) {
            Slog.wtf(TAG, e);
        }
    }

Android只在手机特定场景下触发磁盘整理，未兼容到其他设备。

其他终端可在自定义场景内触发磁盘整理，提升性能，如：

1. 屏保场景
2. 系统升级场景
3. 开机场景
4. 恢复出厂场景
5. App提供主动触发入口

测试数据：

IO读写影响：提升10~20%

应用启动影响：提升5~10%

测试环境：

芯片：MTK9669

备注：不同芯片测试数据差异较大。

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