Date: Sat, 15 Apr 1995 13:02:54 +1000 From: Bruce Evans <bde@zeta.org.au> To: davidg@Root.COM, jgreco@brasil.moneng.mei.com Cc: freebsd-current@FreeBSD.org, hsu@cs.hut.fi Subject: Re: mmap bugs gone yet? Message-ID: <199504150302.NAA01886@godzilla.zeta.org.au>
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>>> With the merged VM/buffer cache, i doubt it will buy too much to mmap
>>> the files at all.
>>
>>This was not true on my Sun 3/60. I never investigated to find out why,
>>however.
> mmap should be faster at accessing files randomly and will eliminate an
>extra copy compared with doing read() system calls. It might be slower when
>modifying large amounts of large files. I think overall mmap would be faster,
>but YYMV.
Does mmap() do read-ahead or read-behind? If it does, then it wouldn't be
so good for random access. If it doesn't then it wouldn't be so good for
seuqential access. What exactly happens if a huge file (larger than
physical memory) is accessed sequentially using read() and mmap()? E.g.,
for simple (simplistic?) copying of files:
read-write:
size = huge; buf = malloc(size); read(0, buf, size); write(1, buf, size);
mmap:
something I can't write without RTFM :-)
Bruce
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