linux-kernel - Re: [PATCH 10/11] writeback: splice dirty inode entries to default bdi on bdi

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Date:	Wed, 16 Sep 2009 20:31:29 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chris.mason@...cle.com, hch@...radead.org, tytso@....edu,
	akpm@...ux-foundation.org, trond.myklebust@....uio.no
Subject: Re: [PATCH 10/11] writeback: splice dirty inode entries to default
	bdi on bdi_destroy()

On Wed, Sep 16 2009, Jan Kara wrote:
> On Wed 16-09-09 15:21:08, Jens Axboe wrote:
> > On Wed, Sep 16 2009, Jan Kara wrote:
> > > On Tue 15-09-09 20:16:56, Jens Axboe wrote:
> > > > We cannot safely ensure that the inodes are all gone at this point
> > > > in time, and we must not destroy this bdi with inodes having off it.
> > >                                                         ^^^ hanging
> > > 
> > > > So just splice our entries to the default bdi since that one will
> > > > always persist.
> > >   BTW: Why can't we make sure all inodes on the BDI are clean when we
> > > destroy it? Common sence would suggest that we better should be able to do
> > > it :).
> > >   Maybe it's because most users of private BDI do not call bdi_unregister
> > > but rather directly bdi_destroy? Is this correct behavior?
> > Not sure yet, it's on the TODO. This basically works around the problem
> > for now at least. With dm at least, I'm seeing inodes still hanging off
> > the bdi after we have done a sync_blockdev(bdev, 1);.
>   Do you really mean sync_blockdev() or fsync_bdev()? Because the first one
> just synces the blockdev's mapping not the filesystem...

Do we want a fsync_bdev() in __blkdev_put()? It's only doing
sync_blockdev() on last close, and dm wants to tear down the device at
that point. So either dm needs to really flush the device when going
readonly, or we need to strengthen the 'flush on last close'.

-- 
Jens Axboe

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