FreeBSD working from RAM (MFSROOT) as a Workstation.

[RW]

On Fri, 05 Dec 2014 00:08:56 -0500
Lowell Gilbert wrote:

> clutton <clutton at 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.


> 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.

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).