linux-kernel - Re: [PATCH -mm] make swapin readahead skip over holes

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Message-ID: <alpine.DEB.2.00.1201111305440.31239@router.home>
Date:	Wed, 11 Jan 2012 13:17:00 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	John Stoffel <john@...ffel.org>
cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH -mm] make swapin readahead skip over holes

On Wed, 11 Jan 2012, John Stoffel wrote:

> KOSAKI> so, we can eat free lunch up to 7MB ~= 60(MB/sec) * 1000 / 8.5(ms).
>
> What if the disk is busy doing other writeout or readin during this
> time?  You can't assume you have the full disk bandwidth available,
> esp when you hit a swap storm like this.

The assumptions by Kosaki are quite conservative.

What if one did not get a disk from the garbage heap but instead has a
state of the art storage cluster or simply an SSD (in particular relevant
now since HDs are in short supply given the situation in Asia)?

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