Re: [PATCH 5/6] writeback: try more writeback as long as something was written

Dave Chinner
2011-04-21T07:53:04Z

On Thu, Apr 21, 2011 at 03:14:26AM -0400, Christoph Hellwig wrote:
> On Thu, Apr 21, 2011 at 05:09:47PM +1000, Dave Chinner wrote:
> > Likely just timing. When IO completes and updates the inode IO size,
> > XFS calls mark_inode_dirty() again to ensure that the metadata that
> > was changed gets written out at a later point in time.
> > Hence every single file that is created by the test will be marked
> > dirty again after the first write has returned and disappeared.
> >
> > Why you see different numbers? it's timing dependent based on Io
> > completion rates - if you have a fast disk the IO completion can
> > occur before write_inode() is called and so the inode can be written
> > and the dirty page state removed in the one writeback_single_inode()
> > call...
> >
> > That's my initial guess without looking at it in any real detail,
> > anyway.
>
> We shouldn't have I_DIRTY_PAGES set for that case, as we only redirty
> metadata. But we're actually doing a xfs_mark_inode_dirty, which
> dirties all of I_DIRTY, which includes I_DIRTY_PAGES. I guess it
> should change to
>
> __mark_inode_dirty(inode, I_DIRTY_SYNC | I_DIRTY_DATASYNC);

Probably should. Using xfs_mark_inode_dirty_sync() might be the best
thing to do.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com