Date: Thu, 2 Aug 2001 13:52:25 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: Rik van Riel <riel@conectiva.com.br> Cc: Terry Lambert <tlambert2@mindspring.com>, craig <craiglei@pasia.com.cn>, freebsd-hackers@FreeBSD.ORG Subject: Re: How to visit physical memory above 4G Message-ID: <Pine.BSF.4.21.0108021350550.41008-100000@InterJet.elischer.org> In-Reply-To: <Pine.LNX.4.33L.0108021528520.5582-100000@duckman.distro.conectiva>
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On Thu, 2 Aug 2001, Rik van Riel wrote: > On Thu, 2 Aug 2001, Julian Elischer wrote: > > On Thu, 2 Aug 2001, Rik van Riel wrote: > > > > > > On the really large machines, this can lead to the > > > situation where even the page tables hardly fit into > > > KVA. 4MB pages seem like the only solution ... > > > > There is no reason why we need to keep the kernel and the user > > process in the same 4GB map except for efficiency. > > > > There have been many UNIX machines in the past which put them in > > separate virtual spaces > > That was on machines where the CPU could actually > address two separate spaces at once, right ? > (like eg. m68k) > > > The kernel would haev 4GB for itself and each process would have 4BG. > > > > System calls would be come more expensive as each would require > > a full page-table swap and a TLB flush. > > However it might be worth it for some people. > > Interrupt handling would also require a full page table > swap and TLB flush. > > Considering that, I think the number of people for whom > this will be worth it has probably dropped a bit ;) True, but it might still be worth it for some people (but not the project as a whole). At one stage I heard that they were thinking of having a separate set of page tables for different security 'rings' but obviously that didn't happen.. > > Rik > -- > Executive summary of a recent Microsoft press release: > "we are concerned about the GNU General Public License (GPL)" > > > http://www.surriel.com/ > http://www.conectiva.com/ http://distro.conectiva.com/ > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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