linux-kernel - Re: [PATCH 2/8] readahead: make default readahead size a kernel parameter

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Date:	Wed, 30 Nov 2011 21:29:28 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Cc:	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ankit Jain <radical@...il.com>, Rik van Riel <riel@...hat.com>,
	Nikanth Karthikesan <knikanth@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 2/8] readahead: make default readahead size a kernel
 parameter

On Wed, Nov 30, 2011 at 09:04:11PM +0800, Christian Ehrhardt wrote:
> 
> 
> On 11/28/2011 03:39 AM, Wu Fengguang wrote:
> > On Fri, Nov 25, 2011 at 08:36:33AM +0800, Dave Chinner wrote:
> >> On Thu, Nov 24, 2011 at 11:28:22PM +0100, Jan Kara wrote:
> >>> On Mon 21-11-11 19:35:40, Wu Fengguang wrote:
> >>>> On Mon, Nov 21, 2011 at 06:01:37PM +0800, Christoph Hellwig wrote:
> >>>>> On Mon, Nov 21, 2011 at 05:18:21PM +0800, Wu Fengguang wrote:
> >>>>>> From: Nikanth Karthikesan<knikanth@...e.de>
> >>>>>>
> [...]
> 
> >>
> >> And one that has already been in use for exactly this purpose for
> >> years. Indeed, it's far more flexible because you can give different
> >> types of devices different default readahead settings quite easily,
> >> and it you can set different defaults for just about any tunable
> >> parameter (e.g. readahead, ctq depth, max IO sizes, etc) in the same
> >> way.
> >
> > I'm interested in this usage, too. Would you share some of your rules?
> >
> 
> FYI - This is an example of a rules Suse delivers in SLES @ s390 for a 
> while now. With little modifications it could be used for all Dave 
> mentioned above.

It's a really good example, thank you!

> cat /etc/udev/rules.d/60-readahead.rules
> # 
>  
>  
> 
> # Rules to set an increased default max readahead size for s390 disk 
> devices 
>  
> 
> # This file should be installed in /etc/udev/rules.d 
>  
>  
> 
> # 
>  
> SUBSYSTEM!="block", GOTO="ra_end" 
> 
> ACTION!="add", GOTO="ra_end" 
> 
> # on device add set initial readahead to 512 (instead of in kernel 128) 
> 
> KERNEL=="sd*[!0-9]", ATTR{queue/read_ahead_kb}="512" 
> 
> KERNEL=="dasd*[!0-9]", ATTR{queue/read_ahead_kb}="512" 

So SLES (@s390 and maybe more) is already shipping with 512kb
readahead size? Good to know this!

Thanks,
Fengguang

>  
> 
> 
> LABEL="ra_end"
> 
> -- 
> 
> Grüsse / regards, Christian Ehrhardt
> IBM Linux Technology Center, System z Linux Performance
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