linux-kernel - Re: kupdate weirdness

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Message-Id: <20070801141439.ff1c29f9.akpm@linux-foundation.org>
Date:	Wed, 1 Aug 2007 14:14:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: kupdate weirdness

On Wed, 01 Aug 2007 22:45:16 +0200
Miklos Szeredi <miklos@...redi.hu> wrote:

> The following strange behavior can be observed:
> 
> 1. large file is written
> 2. after 30 seconds, nr_dirty goes down by 1024
> 3. then for some time (< 30 sec) nothing happens (disk idle)
> 4. then nr_dirty again goes down by 1024
> 5. repeat from 3. until whole file is written
> 
> So basically a 4Mbyte chunk of the file is written every 30 seconds.
> I'm quite sure this is not the intended behavior.
> 
> The reason seems to be that __sync_single_inode() will move the
> partially written inode from s_io onto s_dirty, and sync_sb_inode()
> will not splice it back onto s_io until the rest of the inodes on s_io
> has been processed.

It does all sorts of weird crap.

> Since there will probably be a recently dirtied inode on s_io, this
> will take some of time, but always less than 30 sec.
> 
> I don't know what's the easiest solution.
> 
> Any ideas?

Try 2.6.23-rc1-mm2.
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