Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!snorkelwacker!mintaka!ogicse!blake!Tomobiki-Cho!mrc
From: mrc@Tomobiki-Cho.CAC.Washington.EDU (Mark Crispin)
Newsgroups: comp.arch
Subject: Re: mmap() vs. read() (Was: Re: the Multics from the black lagoon :-))
Message-ID: <5721@blake.acs.washington.edu>
Date: 13 Feb 90 01:38:51 GMT
References: <8859@portia.Stanford.EDU> <20571@watdragon.waterloo.edu> <1990Feb12.053616.11455@Solbourne.COM> <3556@rti.UUCP> <10468@alice.UUCP> <131682@sun.Eng.Sun.COM> <1990Feb13.003010.23356@utzoo.uucp>
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In article <1990Feb13.003010.23356@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>In article <131682@sun.Eng.Sun.COM> gingell@sun.UUCP (Rob Gingell) writes:
>>... At the very least, the read() version will be slower
>>than the mmap() version by the amount of time required to effect the
>>copies from kernel to program buffers...
>
>Assuming your MMU can do copy-on-write, why copy?

I don't see anything that says that read() has to be on a page or
even a word boundary.  I haven't seen a description of mmap(), but
usually file/memory mapping is whole pages on page boundaries, so the
swapper can swap in/out the pages directly from/to the file.

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