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Date:      Fri, 19 Feb 1999 23:20:36 +0000 (GMT)
From:      Terry Lambert <tlambert@primenet.com>
To:        dillon@apollo.backplane.com (Matthew Dillon)
Cc:        toasty@home.dragondata.com, dyson@iquest.net, tlambert@primenet.com, mike@smith.net.au, hackers@FreeBSD.ORG
Subject:   Re: vm_page_zero_fill
Message-ID:  <199902192320.QAA10132@usr02.primenet.com>
In-Reply-To: <199902172020.MAA10702@apollo.backplane.com> from "Matthew Dillon" at Feb 17, 99 12:20:50 pm

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> :What if I'm doing a partial read? Is a partial read even possible if I'm
> :using the mmap method?
> 
>     The filesystem always does a full read even if you only do a partial
>     read.  This is true whether you use read() or access a page w/ mmap(),
>     but it is doubly true with mmap().

The only exception is the perhaps-not-page-aligned last blocks in
the file.

In this case, it zero fills the page before the read, in case of
subsequent file extension.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.


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