Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for WBC_SYNC_ALL writebacks

Theodore Tso
2009-04-07T21:44:49Z

On Tue, Apr 07, 2009 at 09:32:39PM +0200, Jens Axboe wrote:
>
> This should be all you need, forget the below. The manual unplugging
> only really makes sense for very select situations, since it'll be done
> when someone waits on the buffer anyway.

Thanks, ok; I missed the "sync_buffer" in the call to wait_on_bit() in
__wait_on_buffer(). It also wasn't obvious to me that
wait_on_writeback_range() ultimately ends up calling aops->sync_page
which for filemap.c will call blk_run_backing_dev() --- and that
blk_run_*() results in the right device queue getting unplugged. So
this would be a nice thing to get documented in
Documentation/biodoc.txt.

- Ted