Date: Sat, 10 Jan 2009 02:53:43 +0000 From: RW <rwmaillists@googlemail.com> To: freebsd-questions@freebsd.org Subject: Re: how to use the MFS ? Message-ID: <20090110025343.6f0e95d1@gumby.homeunix.com> In-Reply-To: <443afs49ix.fsf@be-well.ilk.org> References: <2c66535d0901082253k5b8ff098w73234a1944929929@mail.gmail.com> <20090109105458.I8836@wojtek.tensor.gdynia.pl> <49672373.3020704@snaffler.net> <2c66535d0901090340y473ce9dcj74ae2a44e5cc0789@mail.gmail.com> <443afs49ix.fsf@be-well.ilk.org>
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On Fri, 09 Jan 2009 13:30:30 -0500 Lowell Gilbert <freebsd-questions-local@be-well.ilk.org> wrote: > "PstreeM China" <pstreem@gmail.com> writes: > > > i think the option WRKDIRPREFIX is a good idea , and i whill test > > the methon unionfs. > > Definitely benchmark against just using a native local filesystem, > though. Taking away all of that memory that FreeBSD would otherwise > use for *caching* file data could well end up making your builds > *slower* with the MFS than they would have been without it. I've a vague recollection that I tried something like this, a few years ago, and found that the difference was too small to measure. I think that however you do it, you basically end-up with something that looks like: CPU/L1/L2 -> memory -> disk and whether the "memory->disk" part is a cached-file or swap-backed memory is really just a matter of book-keeping - the VM system moves the physical memory around as it likes. The book-keeping differences may be significant, but they are not different in the electronic verses electro-mechanical sense, and such intuitions may not relevant. Poul-Henning Kamp, has an interesting article in this area for the varnish project: "I have spent many years working on the FreeBSD kernel, and only rarely did I venture into userland programming, but when I had occation to do so, I invariably found that people programmed like it was still 1975." http://varnish.projects.linpro.no/wiki/ArchitectNotes [Not that there's anything wrong with 1975.]
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