Messages in this thread | | | Date | Thu, 29 Jul 1999 15:04:44 -0400 (EDT) | From | Chuck Lever <> | Subject | Re: clustering page-ins |
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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 -- corporate: <chuckl@netscape.com> personal: <chucklever@netscape.net> or <cel@monkey.org>
The Linux Scalability project: http://www.citi.umich.edu/projects/linux-scalability/
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