linux-kernel - Re: [PATCH 6/7] writeback: separate starting of sync vs opportunistic writeback

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Message-ID: <20090914192803.GL14984@kernel.dk>
Date:	Mon, 14 Sep 2009 21:28:03 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chris.mason@...cle.com,
	tytso@....edu, akpm@...ux-foundation.org,
	trond.myklebust@....uio.no
Subject: Re: [PATCH 6/7] writeback: separate starting of sync vs
	opportunistic writeback

On Mon, Sep 14 2009, Christoph Hellwig wrote:
> On Mon, Sep 14, 2009 at 03:33:07PM +0200, Jan Kara wrote:
> > On Mon 14-09-09 11:36:33, Jens Axboe wrote:
> > > bdi_start_writeback() is currently split into two paths, one for
> > > WB_SYNC_NONE and one for WB_SYNC_ALL. Add bdi_sync_writeback()
> > > for WB_SYNC_ALL writeback and let bdi_start_writeback() handle
> > > only WB_SYNC_NONE.
> >   What I don't like about this patch is that if somebody sets up
> > writeback_control with WB_SYNC_ALL mode set and then submits it to disk via
> > bdi_start_writeback() it will just silently convert his writeback to an
> > asynchronous one.
> >   So I'd maybe leave setting of sync_mode to the caller and just WARN_ON if
> > it does not match the purpose of the function...
> 
> Or initialize the wb entirely inside these functions.  For the sync case
> we really only need a superblock as argument, and for writeback it's
> bdi + nr_pages.  And also make sure they consistenly return void as
> no one cares about the return value.

Yes, I thought about doing that and like that better than the warning.
Just pass in the needed args and allocate+fill the wbc on stack. I'll
make that change.

-- 
Jens Axboe

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