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

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Message-ID: <20237.63802.982209.699996@quad.stoffel.home>
Date:	Wed, 11 Jan 2012 16:03:54 -0500
From:	"John Stoffel" <john@...ffel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	John Stoffel <john@...ffel.org>,
	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

>>>>> "Christoph" == Christoph Lameter <cl@...ux.com> writes:

Christoph> 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.

Christoph> The assumptions by Kosaki are quite conservative.

Just checking

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

I don't know, I was just trying to make sure he thinks about disks
which are slower than he expects, since there are lots of them still
out there.  

John

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