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.