Date: Fri, 27 Feb 2004 14:17:17 +0000 From: Chris Elsworth <chris@shagged.org> To: Colin Percival <colin.percival@wadham.ox.ac.uk> Cc: freebsd-current@freebsd.org Subject: Re: mdconfig unable to allocate memory Message-ID: <20040227141717.GA53143@shagged.org> In-Reply-To: <6.0.1.1.1.20040227140137.03e01818@imap.sfu.ca> References: <20040227101410.GA45369@shagged.org> <xzpwu68d4xy.fsf@dwp.des.no> <20040227135836.GA52534@shagged.org> <6.0.1.1.1.20040227140137.03e01818@imap.sfu.ca>
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On Fri, Feb 27, 2004 at 02:08:48PM +0000, Colin Percival wrote: > At 13:58 27/02/2004, Chris Elsworth wrote: > >So, in short, is there any rule of thumb to follow when tweaking these > >settings? > > Yes, several: > 1. Don't do it. > 2. Pray. > 3. Don't do it. > 4. If you absolutely must do it, make sure you have a serial console > connected. > 5. Don't do it. Right, got it :) Having the machine crash is no problem. It's sat in my lounge, so I can tweak and reboot and restore from kernel.generic to my hearts content. This seems to be a problem that's been gone over and over and over again, but never with any clear answer according to Google. Given a FreeBSD machine with 4GB in it, be it 4 or 5, how can one ensure that all the memory is being used for suitable file caching if it's running MySQL? I was aiming at raising vfs.maxbufspace to be 2GB or so. Since that was just resuling in kernel panics pretty much whatever I tried, I was giving mdconfig a go. > > It's a bit worrying that an out of the box 5.2.1 managed to > >crash at all. > > The fact that running out of kernel address space can cause > problems is quite well documented. Well, yes, but why would "vinum start" on a clean boot before any tweaking (this is an out of the box 5.2.1-R) cause that? Surely the kernel address space is sufficiently large just by self-tuning on a machine with 4GB, for a vinum start to succeed? > Why do you want to have a GB malloc-backed disk anyway? This machine is for MySQL, and there's a wild un-backed-up claim on a mysql list that moving MySQL indexes into a ramdisk (they're all trashable data and easily recreateable) can give a fourfold performance increase. So I wanted to try it. In order to get them all in there, though, I'm going to need at least 2GB. I think I'm just missing the point of having a swap backed memory disk, really; I assumed that it would immediately start dumping anything I put in it, into swap, causing disk access. Does it only put stuff into swap once it runs out of address space? -- Chris
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