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Date: Thu, 21 Apr 2011 03:14:26 -0400
From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 5/6] writeback: try more writeback as long as something
 was written
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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);