From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/8] block: limit default readahead size for small devices
Date: Mon, 21 Nov 2011 05:00:04 -0500
Message-ID: <20111121100004.GB5084@infradead.org>
References: <20111121091819.394895091@intel.com>
 <20111121093846.121502745@intel.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-fsdevel@vger.kernel.org, Li Shaohua <shaohua.li@intel.com>,
	Clemens Ladisch <clemens@ladisch.de>,
	Jens Axboe <jens.axboe@oracle.com>,
	Rik van Riel <riel@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andi Kleen <andi@firstfloor.org>
To: Wu Fengguang <fengguang.wu@intel.com>
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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?