linux-ext4 - Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for WBC_SYNC

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Message-ID: <20090407214421.GA7031@mit.edu>
Date:	Tue, 7 Apr 2009 17:44:21 -0400
From:	Theodore Tso <tytso@....edu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	jack@...e.cz
Subject: Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for
	WBC_SYNC_ALL writebacks

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
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