From owner-freebsd-current Wed Jul 7 19:36:26 1999 Delivered-To: freebsd-current@freebsd.org Received: from mycenae.ilion.eu.org (mycenae.ilion.eu.org [203.35.206.129]) by hub.freebsd.org (Postfix) with ESMTP id E839814BD8; Wed, 7 Jul 1999 19:36:15 -0700 (PDT) (envelope-from patrykz@mycenae.ilion.eu.org) Received: from mycenae.ilion.eu.org (patrykz@localhost [127.0.0.1]) by mycenae.ilion.eu.org (8.9.2/8.9.2) with ESMTP id MAA16726; Thu, 8 Jul 1999 12:36:01 +1000 (EST) (envelope-from patrykz@mycenae.ilion.eu.org) Message-Id: <199907080236.MAA16726@mycenae.ilion.eu.org> To: Greg Lehey Cc: Peter Jeremy , freebsd-current@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: Bursting at the seams (was: Heh heh, humorous lockup) In-reply-to: Your message of "Thu, 08 Jul 1999 11:04:47 +0930." <19990708110446.P2340@freebie.lemis.com> Date: Thu, 08 Jul 1999 12:36:01 +1000 From: Patryk Zadarnowski Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > Why not put the kernel in a different address space? IIRC there's no > absolute requirement for the kernel and userland to be in the same > address space, and that way we would have 4 GB for each. Wouldn't that make system calls that need to share data between kernel and user spaces hopelessly inefficient? Things like sysctl() would need to introduce (temporary) memory mappings, and someone would have to keep track of these mappings and remove them as required, or the kernel would probably run out of address space in no time, given even with 4GB to spare. On top of that, every mapping established requires some messing arround with the TLB, which, at least on pentium, is rather expensive. Incidentally, someone already experimented with such "dual" address spaces on Linux, and the result was a 30% or so slow down. If you're interested, I can give you the relevant references (the scenario was somewhat different, but the source of the performance hit was the "dual" address space.) patryk. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message