Subject: Re: [PATCH] Improve buffered streaming write ordering
From: Chris Mason <chris.mason@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-fsdevel <linux-fsdevel@vger.kernel.org>,
       ext4 <linux-ext4@vger.kernel.org>
In-Reply-To: <20081002234309.GH30001@disturbed>
References: <1222886451.9158.34.camel@think.oraclecorp.com>
	 <20081001215239.ee2ae63f.akpm@linux-foundation.org>
	 <1222950054.6745.18.camel@think.oraclecorp.com>
	 <20081002181856.GB29613@skywalker>  <20081002234309.GH30001@disturbed>
Content-Type: text/plain
Date: Fri, 03 Oct 2008 15:45:55 -0400
Message-Id: <1223063155.13375.64.camel@think.oraclecorp.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, 2008-10-03 at 09:43 +1000, Dave Chinner wrote:
> On Thu, Oct 02, 2008 at 11:48:56PM +0530, Aneesh Kumar K.V wrote:
> > On Thu, Oct 02, 2008 at 08:20:54AM -0400, Chris Mason wrote:
> > > On Wed, 2008-10-01 at 21:52 -0700, Andrew Morton wrote:
> > > For a 4.5GB streaming buffered write, this printk inside
> > > ext4_da_writepage shows up 37,2429 times in /var/log/messages.
> > > 
> > 
> > Part of that can happen due to shrink_page_list -> pageout -> writepagee
> > call back with lots of unallocated buffer_heads(blocks).
> 
> Quite frankly, a simple streaming buffered write should *never*
> trigger writeback from the LRU in memory reclaim.

The blktrace runs on ext4 didn't show kswapd doing any IO.  It isn't
clear if this is because ext4 did the redirty trick or if kswapd didn't
call writepage.

-chris


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