linux-kernel - Re: fs: Inode cache scalability V3

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Date:	Thu, 14 Oct 2010 10:55:52 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...nel.dk
Subject: Re: fs: Inode cache scalability V3

On Wed, Oct 13, 2010 at 07:36:48PM -0400, Christoph Hellwig wrote:
> On Wed, Oct 13, 2010 at 05:46:09PM -0400, Christoph Hellwig wrote:
> > On Wed, Oct 13, 2010 at 11:58:45AM -0400, Christoph Hellwig wrote:
> > > 
> > > It's 100% reproducible on my kvm VM.  The bug is the assert_spin_locked
> > > in redirty_tail.  I really can't find a way how we reach it without
> > > d_lock so this really confuses me.
> > 
> > We are for some reason getting a block device inode that is on the
> > dirty list of a bdi that it doesn't point to.  Still trying to figure
> > out how exactly that happens.
> 
> It's because __blkdev_put reset the bdi on the mapping, and bdev inodes
> are still special cased to not use s_bdi unlike everybody else.  So
> we keep switch between different bdis that get locked.
> 
> I wonder what's a good workaround for that.  Just flushing out all
> dirty state of a block device inode on last close would fix, but we'd
> still have all the dragons hidden underneath until we finally sort
> out the bdi reference mess.

Perhaps for the moment make __blkdev_put() move the inode onto the
dirty lists for the default bdi when it switches themin the
mapping? e.g. add a "inode_switch_bdi" helper that is only called in
this case?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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