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

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Date:	Wed, 30 Nov 2011 14:04:11 +0100
From:	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
To:	Wu Fengguang <fengguang.wu@...el.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 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.

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" 
 
 


LABEL="ra_end"

-- 

Grüsse / regards, Christian Ehrhardt
IBM Linux Technology Center, System z Linux Performance

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