linux-kernel - Re: [PATCH 03/17] writeback: introduce writeback_control.inodes

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Message-ID: <20110506143614.GF18982@quack.suse.cz>
Date:	Fri, 6 May 2011 16:36:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mel@....ul.ie>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 03/17] writeback: introduce
 writeback_control.inodes_cleaned

On Fri 06-05-11 11:08:24, Wu Fengguang wrote:
> The flusher works on dirty inodes in batches, and may quit prematurely
> if the batch of inodes happen to be metadata-only dirtied: in this case
> wbc->nr_to_write won't be decreased at all, which stands for "no pages
> written" but also mis-interpreted as "no progress".
> 
> So introduce writeback_control.inodes_cleaned to count the inodes get
> cleaned.  A non-zero value means there are some progress on writeback,
> in which case more writeback can be tried.
> 
> about v1: The initial version was to count successful ->write_inode()
> calls.  However it leads to busy loops for sync() over NFS, because NFS
> ridiculously returns 0 (success) while at the same time redirties the
> inode.  The NFS case can be trivially fixed, however there may be more
> hidden bugs in other filesystems..
  I think Christoph didn't like this patch
(https://lkml.org/lkml/2011/5/4/123) and suggested that inodes_cleaned
should remain local to fs-writeback.c...

								Honza

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