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- Newsgroups: comp.lang.lisp,comp.lang.c++,comp.lang.c,comp.lang.misc,comp.theory
- Path: newsfeed.ed.ac.uk!edcogsci!jeff
- From: jeff@cogsci.ed.ac.uk (Jeff Dalton)
- Subject: Re: allocator studies (was Re: GC & traditional allocators & textbooks)
- Message-ID: <DMD9Bx.6qq.0.macbeth@cogsci.ed.ac.uk>
- Organization: Centre for Cognitive Science, Edinburgh, UK
- References: <4f2ila$6p8@jive.cs.utexas.edu> <823455623snz@wildcard.demon.co.uk> <4f59c3$7il@jive.cs.utexas.edu>
- Distribution: inet
- Date: Tue, 6 Feb 1996 18:14:21 GMT
-
- In article <4f59c3$7il@jive.cs.utexas.edu> wilson@cs.utexas.edu (Paul Wilson) writes:
- >In article <823455623snz@wildcard.demon.co.uk>,
- >Cyber Surfer <cyber_surfer@wildcard.demon.co.uk> wrote:
- >>In article <4f2ila$6p8@jive.cs.utexas.edu>
- >> wilson@cs.utexas.edu "Paul Wilson" writes:
- >>
- >>> The history of allocator
- >>> research has been a big mess---the literature is a bit of a disaster
- >>> area---and the textbooks reflect this. The analyses in the books are
- >>> shallow and largely wrong. [...]
- >>
- >>I won't argue with that! ;-) I'd love to see a good summary.
- >
- >Well, very briefly:
- >
- > [...]
- >
- > 5. The best-known policies (best fit and address-ordered first fit)
- > work better than anyone ever knew, while some policies (Knuth's
- > "Modified First Fit" or "Next Fit") work worse than anyone ever
- > knew, for some programs. This is because randomized traces tend
- > probabilistically to ensure that certain important realistic
- > program behaviors will never happen in traditional experiments.
-
- > [...]
-
- >>> "Modified First Fit" with the roving pointer is the clearest example. It
- >>> was a bad idea, and it was quickly shown to be bad, but some other
- >>> textbook writers keep mindlessly cribbing from Knuth, [...]
-
- When I was a student, there was a course in which people implemented
- various alloc/free policies, to compare them experimentally. They got
- results rather different from the ones suggested by Knuth but were
- reluctant to draw the conclusion that Knuth might be wrong. I'm not
- sure how they convinced the instructor that they hadn't blown it.
- (I've forgotten the experimental details, I'm afraid.)
-
- Anyway, for some reason, I've experienced pretty good performance from
- mark-and-sweep GCs, and without much in the way of long pauses, both
- with Lisp systems and with implementations of strings. The really
- slow, long pause, GCs I've encountered were copying ones.
-
- -- jd
-
-
-
-