Date: Thu, 2 Aug 2001 13:30:54 -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.4.21.0108021325410.41008-100000@InterJet.elischer.org> In-Reply-To: <Pine.LNX.4.33L.0108020728100.5582-100000@duckman.distro.conectiva>
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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 and we have kept those interfaces exactly so that we have the option of doing it one day.. e.g. copyin and copyout could copy to a totally different VM space. 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. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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