From: Valdis.Kletnieks@vt.edu
To: Ian Stirling <tandra@mauve.plus.com>
Cc: yunfeng zhang <zyf.zeroos@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Improvement on memory subsystem
Date: Wed, 19 Jul 2006 10:56:32 -0400 [thread overview]
Message-ID: <200607191456.k6JEuW0x004945@turing-police.cc.vt.edu> (raw)
In-Reply-To: Your message of "Wed, 19 Jul 2006 10:18:44 BST." <44BDF8F4.30908@mauve.plus.com>
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On Wed, 19 Jul 2006 10:18:44 BST, Ian Stirling said:
> To paraphrase shakespear - all the world is not a P4 - and all the swap
> devices are not hard disks.
Been there, done that. I used to admin a net of Sun 3/50s where /dev/swap
was a symlink to a file on an NFS server, because the "shoebox" local hard
drives for those were so slow that throwing it across the ethernet to a
3/280 with Fujitsu Super-Eagles was faster...
> For example - I've got a 486/33 laptop with 12M RAM that I sometimes use
> , with swapping to a 128M PCMCIA RAM card that I got from somewhere.
If we go to the effort of writing code that tries to be smart about grouping
swap reads/writes by cost, it's easy enough to flag any sort of ram-disk device
as a 'zero seek time' device. Remember that I suggested making it dependent
on "how long until the next pass of the elevator" - for a ramdisk that basically
is zero, so the algorithm easily degenerates into "just queue the requests in
expected order you'll need the results".
> 20K instructions wasted on a device with no seek time is just annoying.
On the other hand, how long does it take to move a 4K page across the
PCMCIA interface? If you're seeing deep queues on it, you may *still*
want to optimize the order of requests...
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next prev parent reply other threads:[~2006-07-19 14:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-18 10:03 Improvement on memory subsystem yunfeng zhang
2006-07-18 12:18 ` Valdis.Kletnieks
2006-07-19 3:44 ` yunfeng zhang
2006-07-19 9:18 ` Ian Stirling
2006-07-19 14:56 ` Valdis.Kletnieks [this message]
2006-07-18 16:25 ` Pekka Enberg
2006-07-19 3:21 ` yunfeng zhang
2006-07-19 8:30 ` Pekka Enberg
2006-07-19 10:13 ` yunfeng zhang
2006-07-19 10:35 ` Pekka Enberg
2006-07-24 9:01 ` yunfeng zhang
2006-07-24 14:55 ` David Lang
2006-07-25 8:33 ` yunfeng zhang
2006-08-23 10:39 ` yunfeng zhang
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