linux-ext4 - Re: ext4 writepages is making tiny bios?

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Message-ID: <20090904072013.GR18599@kernel.dk>
Date:	Fri, 4 Sep 2009 09:20:13 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Theodore Tso <tytso@....edu>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: ext4 writepages is making tiny bios?

On Thu, Sep 03 2009, Theodore Tso wrote:
> On Thu, Sep 03, 2009 at 12:42:09PM -0400, Christoph Hellwig wrote:
> > > Careful:
> > > 
> > > -	tloff = min(tlast, startpage->index + 64);
> > > +	tloff = min(tlast, startpage->index + 8192);
> > > 
> > > That will cause 64k page machines to try to write back 512MB at a
> > > time. This will re-introduce similar to the behaviour in sles9 where
> > > writeback would only terminate at the end of an extent (because the
> > > mapping end wasn't capped like above).
> > 
> > Pretty good point, any applies to all the different things we discussed
> > recently.  Ted, should be maybe introduce a max_writeback_mb instead of
> > the max_writeback_pages in the VM, too?
> 
> Good point.
> 
> Jens, maybe we should replace my patch with this one, which makes the
> tunable in terms of megabytes instead of pages?

That is probably a better metric than 'pages', lets update it.

-- 
Jens Axboe

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