Re: [PATCH 2/6] writeback: wb_start_writeback() should use WB_SYNC_ALL for WB_REASON_SYNC

From: Dave Chinner
Date: Tue Mar 22 2016 - 17:35:11 EST

On Tue, Mar 22, 2016 at 11:55:16AM -0600, Jens Axboe wrote:
> If you call sync, the initial call to wakeup_flusher_threads() ends up
> calling wb_start_writeback() with reason=WB_REASON_SYNC, but
> wb_start_writeback() always uses WB_SYNC_NONE as the writeback mode.
> Ensure that we use WB_SYNC_ALL for a sync operation.

This seems wrong to me. We want background write to happen as
quickly as possible and /not block/ when we first kick sync.

The latter blocking passes of sync use WB_SYNC_ALL to ensure that we
block waiting for all remaining IO to be issued and waited on, but
the background writeback doesn't need to do this.


Dave Chinner