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

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Message-ID: <20111121124715.GD24062@one.firstfloor.org>
Date:	Mon, 21 Nov 2011 13:47:15 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	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 05:00:04AM -0500, Christoph Hellwig wrote:
> On Mon, Nov 21, 2011 at 05:18:20PM +0800, Wu Fengguang wrote:
> > 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?

The more the IOPs the larger the "window" you need to keep everything
going I suspect.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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