linux-kernel - Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY

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Date:	Mon, 24 Aug 2015 21:08:47 +0200
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Eryu Guan <eguan@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel@...r.kernel.org, xfs@....sgi.com, axboe@...com,
	Jan Kara <jack@...e.com>, linux-fsdevel@...r.kernel.org,
	kernel-team@...com
Subject: Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME
 inodes

On Mon 24-08-15 13:11:44, Tejun Heo wrote:
> Hello,
> 
> On Mon, Aug 24, 2015 at 10:51:50AM -0400, Tejun Heo wrote:
> > > Bah, I see the problem and indeed it was introduced by commit e79729123f639
> > > "writeback: don't issue wb_writeback_work if clean". The problem is that
> > > we bail out of sync_inodes_sb() if there is no dirty IO. Which is wrong
> > > because we have to wait for any outstanding IO (i.e. call wait_sb_inodes())
> > > regardless of dirty state! And that also explains why Tejun's patch fixes
> > > the problem because it backs out the change to the exit condition in
> > > sync_inodes_sb().
> > 
> > Dang, I'm an idiot sandwich.
> 
> A question tho, so this means that an inode may contain dirty or
> writeback pages w/o the inode being on one of the dirty lists.
> Looking at the generic filesystem and writeback code, this doesn't
> seem true in general.  Is this something xfs specific?

Inode may contain writeback pages (but not dirty pages) without being on
any of the dirty lists. That is correct. Josef Bacik had patches to create
a list to track inodes with pages under writeback but they clashed with
your patch series and they didn't get rebased yet AFAIR.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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