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Date: Mon, 7 Oct 2002 12:24:36 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: Daniel Phillips <phillips@arcor.de>
cc: Andrew Morton <akpm@digeo.com>, "Martin J. Bligh" <mbligh@aracnet.com>,
       Oliver Neukum <oliver@neukum.name>, Rob Landley <landley@trommello.org>,
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Subject: Re: The reason to call it 3.0 is the desktop (was Re: [OT] 2.6 not
 3.0 -  (NUMA))
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On Mon, 7 Oct 2002, Daniel Phillips wrote:
> 
> Devices have a few MB of readahead cache, the kernel can have thousands of
> times as much.

I don't think that is in the least realistic.

There's _no_ way that the krenel could do physical readahead for more than
a few tens or hundreds of kB - the latency impact would just be too much
to handle, and the VM impact is not likely insignificant either.

So the device readahead is _not_ noticeably smaller than what the kernel
can reasonably do, and it does a better job of it (ie disks can fill track
buffers optimally, depending on where the head hits etc).

		Linus

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