linux-kernel - Re: [PATCH 1/8] block: limit default readahead size for small devices

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Date:	Mon, 21 Nov 2011 19:24:09 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Clemens Ladisch <clemens@...isch.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 1/8] block: limit default readahead size for small
 devices

On Mon, Nov 21, 2011 at 06:00:04PM +0800, Christoph Hellwig wrote:
> On Mon, Nov 21, 2011 at 05:18:20PM +0800, Wu Fengguang wrote:
> > This looks reasonable: smaller device tend to be slower (USB sticks as
> > well as micro/mobile/old hard disks).
> > 
> > Given that the non-rotational attribute is not always reported, we can
> > take disk size as a max readahead size hint. This patch uses a formula
> > that generates the following concrete limits:
> 
> Given that you mentioned the rotational flag and device size in this
> mail, as well as benchmarking with an intel SSD  -  did you measure
> how useful large read ahead sizes still are with highend Flash device
> that have extremly high read IOP rates?

I don't know -- I don't have access to such highend devices.

However the patch changelog has the simple test script. It would be
high appreciated if someone can help collect the data :)

Thanks,
Fengguang
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