Date: Fri, 05 Dec 2014 10:34:45 -0500 From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org> To: RW <rwmaillists@googlemail.com> Cc: freebsd-questions@freebsd.org Subject: Re: FreeBSD working from RAM (MFSROOT) as a Workstation. Message-ID: <4461dqf6ui.fsf@lowell-desk.lan> In-Reply-To: <20141205131229.5ebd96d2@gumby.homeunix.com> (RW's message of "Fri, 5 Dec 2014 13:12:29 %2B0000") References: <1417734458.1772.1.camel@zoho.com> <447fy665uf.fsf@be-well.ilk.org> <20141205131229.5ebd96d2@gumby.homeunix.com>
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RW <rwmaillists@googlemail.com> writes: > On Fri, 05 Dec 2014 00:08:56 -0500 > Lowell Gilbert wrote: > >> clutton <clutton@zoho.com> 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"
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