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

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Date:	Wed, 11 Jan 2012 09:11:23 -0500
From:	"John Stoffel" <john@...ffel.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	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

>>>>> "KOSAKI" == KOSAKI Motohiro <kosaki.motohiro@...il.com> writes:

>> Also, I doubt current swap_cluster default is best value on nowadays.
KOSAKI> I meant, current average hdd spec is,
KOSAKI>  - average seek time: 8.5ms
KOSAKI>  - sequential access performance: about 60MB/sec

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.  

John
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