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

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Date:	Tue, 10 May 2011 10:23:36 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Mel Gorman <mel@....ul.ie>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 03/17] writeback: introduce
 writeback_control.inodes_cleaned

On Fri, May 06, 2011 at 10:36:14PM +0800, Jan Kara wrote:
> 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...

Yes, he didn't like introducing one more field to writeback_control,
which will be removed in patch 14. (It will be a lot of fuss to move
patch 14 here or move this logic after patch 14.)

Thanks,
Fengguang
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