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

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Message-ID: <20111121100004.GB5084@infradead.org>
Date:	Mon, 21 Nov 2011 05:00:04 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.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 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?

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