Date: Tue, 27 Nov 2001 23:40:04 -0600 From: Mike Meyer <mwm@mired.org> To: swear@blarg.net (Gary W. Swearingen) Cc: David Kirchner <davidk@accretivetg.com>, Anthony Atkielski <anthony@freebie.atkielski.com>, <questions@FreeBSD.ORG> Subject: Re: Calculating swap file size Message-ID: <15364.30900.812049.261873@guru.mired.org> In-Reply-To: <kry9krscd0.9kr@localhost.localdomain> References: <20011127170344.W15780-100000@localhost> <kry9krscd0.9kr@localhost.localdomain>
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Gary W. Swearingen <swear@blarg.net> types: > David Kirchner <davidk@accretivetg.com> writes: > > On Tue, 27 Nov 2001, Mike Meyer wrote: > > > The VM algorithms aren't quite as efficient if you have less than 2x > > > ram size. > Don't read more out of tuning(7) than was written into it. It says: > > The kernel's VM paging algorithms are tuned to perform best when > there is at least 2x swap versus main memory. Configuring too > little swap can lead to inefficiencies in the VM page scanning code > > Man page tuning(7) doesn't imply that a 64 MB RAM system will swap 10 MB > faster with 128 MB swap than with 64 MB swap (and I wouldn't believe it > if it did, without some evidence or explanation.) Actually I don't > think it even implies that it would be more efficient. I disagree about that interpretation, though at the levels of your example it might not be measurable. But I think it implies that if you're swapping 32MB of 64MB, it will be more efficient with 128MB of swap than with 40MB. > I'm gusssing that it might swap 64 MB of 128 MB swap less than twice as > slowly than 32 MB of 64 MB swap (or some such thing that doesn't > directly impact user swap sizing). That's the only kind of "algorithm > performance tuning" neccessary to justify the broad statements of > tuning(7). I agree that such is sufficient, but I don't think it's necessary. At least one other person agrees that the wording in tuning may imply more than is true, and is discussing the matter with Matt. FWIW, my favorite swap configuration is two RAM+64K partitions on two different disks, on two different controllers if they're IDE drives. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Q: How do you make the gods laugh? A: Tell them your plans. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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