From owner-freebsd-questions@FreeBSD.ORG Fri Dec 5 15:34:54 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 1AFCB5C6 for ; Fri, 5 Dec 2014 15:34:54 +0000 (UTC) Received: from be-well.ilk.org (be-well.ilk.org [23.30.133.173]) by mx1.freebsd.org (Postfix) with ESMTP id E059FC2A for ; Fri, 5 Dec 2014 15:34:53 +0000 (UTC) Received: from lowell-desk.lan (lowell-desk.lan [172.30.250.41]) by be-well.ilk.org (Postfix) with ESMTP id 1BE2F33C1D; Fri, 5 Dec 2014 10:34:48 -0500 (EST) Received: by lowell-desk.lan (Postfix, from userid 1147) id 0169B39813; Fri, 5 Dec 2014 10:34:46 -0500 (EST) From: Lowell Gilbert To: RW Subject: Re: FreeBSD working from RAM (MFSROOT) as a Workstation. References: <1417734458.1772.1.camel@zoho.com> <447fy665uf.fsf@be-well.ilk.org> <20141205131229.5ebd96d2@gumby.homeunix.com> Date: Fri, 05 Dec 2014 10:34:45 -0500 In-Reply-To: <20141205131229.5ebd96d2@gumby.homeunix.com> (RW's message of "Fri, 5 Dec 2014 13:12:29 +0000") Message-ID: <4461dqf6ui.fsf@lowell-desk.lan> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain Cc: freebsd-questions@freebsd.org X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 05 Dec 2014 15:34:54 -0000 RW writes: > On Fri, 05 Dec 2014 00:08:56 -0500 > Lowell Gilbert wrote: > >> clutton writes: >> >> > Is anyone use a FreeBSD as a Desktop working from RAM, using >> > MFSROOT? >> >> That only speeds up the *first* load of each memory page mirroring a >> disk sector. After the system has been up a while, it's actually >> slower than running with a disk, because everything you actually use >> will have two copies in RAM: one on the disk image, and the one >> that's actually occupying normal resident pages. > > I don't know much about MFSROOT, but I doubt that's right. It seems > unlikely that the kernel caches ram in ram, the normal expectation is > that a single copy of a page is used until it needs to be > copied-on-write. You're right. The md device creates VM objects directly. >> TL;DR: To run from RAM, you first have to load the RAM. The chances >> that an MFSROOT does this more efficiently (than starting directly >> from the nonvolatile disk) seem remote. > > It depends on what you care about. If you aren't bothered by the > time it takes to boot, on a desktop it may be preferable take a lot of > separate reads off the critical path. You're losing some efficiency in how programs get loaded, but once you're off the "critical path," nobody cares. > An alternative might be to do a conventional boot and then kick-off a > background script that pre-caches as much of the SSD as will fit in the > remaining free memory. I'd try this first because it's a lot less > trouble and will give a reasonable indication of how much thing can be > speeded-up (at least until the cache is driven-out by something else). > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org"