Re: clustering page-ins
Chuck Lever (cel@monkey.org)
Thu, 29 Jul 1999 15:04:44 -0400 (EDT)
On Tue, 27 Jul 1999, Jamie Lokier wrote:
> If the sweep is relatively fast you want either (a) large clusters or
> (b) to trigger read-ahead _several clusters_ ahead. Specifically, the
> trigger point has to be N pages ahead, where N is going to imply large
> clusters or many smaller clusters. Very large clusters are bad
> because they use a lot of memory, and the large requests hog the I/O
> subsystem.
>
> If the sweep is relatively slow, for minimal read-ahead page usage,
> trigger read-ahead near the end of the previously read segment.
> However the segments will be quite small in this case, so triggering
> at the beginning of the previously read segment (Steven's suggestion)
> seems fine.
all the read-ahead and clustering parameters are adustable, but how do you
propose to measure the sweep rate? how can we tell when a cluster becomes
very large, and thus is affecting other I/O bound jobs?
- Chuck Lever
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