Date: Mon, 28 Jun 1999 01:41:58 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Daniel J. O'Connor" <darius@dons.net.au> Cc: Ladavac Marino <mladavac@metropolitan.at>, freebsd-hackers@FreeBSD.ORG, Zhihui Zhang <zzhang@cs.binghamton.edu> Subject: Re: RE: Implementation of mmap() in FreeBSD Message-ID: <199906280841.BAA18494@apollo.backplane.com> References: <XFMail.990628175309.darius@dons.net.au>
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:> [ML] It is possible to handle these cases in VM code, by
:> trapping on any access to the partial page, and allowing only those
:> accesses which are withing the originally requested range. Performance
:> would suck without end, though.
:
:Well it would only suck for access to that page right, which wouldn't be too
:bad unless the program in question thrashes out the partial pages.
:
:---
:Daniel O'Connor software and network engineer
I don't think this would be workable. It would fail utterly on small
files -- every single access would be trapped. The system must be
reasonably deterministic. Programmers have a reasonable expectation
that accesses to mmap'd areas are, for in-core pages, instantanious.
Otherwise they wouldn't bother to use mmap and instead would use read()
and write() :-)
-Matt
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