linux-kernel - Re: speeding up swapoff

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Date:	Thu, 30 Aug 2007 15:55:01 +0200
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	Robert Hancock <hancockr@...w.ca>
CC:	Daniel Drake <ddrake@...ntes3d.com>,
	Arjan van de Ven <arjan@...radead.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: speeding up swapoff

Robert Hancock wrote:
> Daniel Drake wrote:
>> On Wed, 2007-08-29 at 07:30 -0700, Arjan van de Ven wrote:
>>>> My experiments show that when there is not much free physical memory,
>>>> swapoff moves pages out of swap at a rate of approximately 5mb/sec.
>>> sounds like about disk speed (at random-seek IO pattern)
>>
>> We are only using 'standard' seagate SATA disks, but I would have
>> thought much more performance (40+ mb/sec) would be reachable.
>
> Not if it is doing random seeks..
If the swap device is full, then there is no need for random
seeks as the swap pages can be read in disk order. A not
so full swap will skip over the unused areas, the time
needed should still be limited to the time needed for reading the
whole swap device.

If this optimization is worth it is another problem though.

Helge Hafting
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