Re: Swap space question
Years ago (well about two or three years ago) I worked as a sysadmin in a university. Early implementations of swap required you to have swap, because the kernel would always look for it to see if it was swapped in. The swap had to be equivalent to or larger than your physical ram. I actually used to use much more swap space on old Sun systems 5x to 10x, and it would go into conniption fits from when we had too many students log into the server. (At the time RAM was relatively expensive, as were servers). The newer kernels both Sparc and Linux (includian Debian Linux of course), and I'm sure someone will correct me if I'm wrong, use very sophisticated algorithms to use swap as additional memory instead of simply keeping an image of memory in the swap space and paging the frames into and out of RAM. So the newer kernels can use swap space which is smaller than physical RAM. I could easily have 512M or RAM and use 256M of swap and everything would work fine. It would be close to having 768M of RAM except for a little overhead. On Tue, May 02, 2000 at 04:37:46PM +1000, Michael Anthon wrote: > > When I first installed Debian Sparc from the CD, I partitioned a Gig > > of Swap space since I have half a Gig of Ram. The Slink kernel would > > I have often seen this "rule of thumb" used in this way and I believe that > it has long been misinterpreted. The rule that I am talking about is "you > need at least twice the amount of swap space as you have RAM". Currently I have needed no swap and in face have yet to use more than about 200M or RAM. [ I suspect that poorly written code and bugs in some applications, or some applications on an SMP kernel are the only reason I've used that much RAM.] > > I am pretty sure that the original interpretation of this rule was more > along the lines of "determine how much memory you will need to run > everything you need to run, then make sure that at least 1/3 of that is > physical RAM". > > The intention here is a trade off between system performance and cost. > Hardware has, however, progressed to a point where this rule is pretty much > useless for normal systems. If you are running a machine with 512M of RAM, Systems with 512M of RAM are never normal systems and wont be until we progress through four or five more generations of computers. (later this week?). I will be using Squid and MySQL very heavily. The machine is being configured as a proxy server, database server, and web server. One of the joys of Squid is that it will keep as much in memory as it can without triggering swap, if it is well configured. This will mean that when I get a request for a web page from the proxy server it should go out instantly instead of having to be retrieved from the cache on disk. I haven't experimented much with MySQL or SQUID in this environmented, so I'm making a lot of guesses. > then you probably don't really need to configure any swap space at all > unless the machine will need it for running a big database or some other > memory hungry application. That 1G of swap space could be used for a much > better purpose (like storing 1G of pron or mp3s.. hehe). If you ever really > do need the extra memory, simple create a swap partition and use swapon as > the need arises. > > Just my $0.02 (+10%GST) worth. > > Regards > Michael Anthon > > > -- > To UNSUBSCRIBE, email to [EMAIL PROTECTED] > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED] -- Josh Kuperman [EMAIL PROTECTED]
Re: Swap space question
On Tue, May 02, 2000 at 04:37:46PM +1000, Michael Anthon wrote: > I have often seen this "rule of thumb" used in this way and I believe that > it has long been misinterpreted. The rule that I am talking about is "you > need at least twice the amount of swap space as you have RAM". IIRC, it's a BSDism. On panics, the kernel shoves an image of itself into the swap. One needs at least the amount of ram, plus some extra wiggle-room, to do so. I may be wrong. No, really! It is possible! - chad -- Chad Miller <[EMAIL PROTECTED]> URL: http://web.chad.org/ "Any technology distinguishable from magic is insufficiently advanced". First corollary to Clarke's Third Law (Jargon File, v4.2.0, 'magic')
RE: Swap space question
On Tue, 2 May 2000, Michael Anthon wrote: > I am pretty sure that the original interpretation of this rule was more > along the lines of "determine how much memory you will need to run > everything you need to run, then make sure that at least 1/3 of that is > physical RAM". Actually, apparently, long ago, the amount of swap you had directly equaled the amount of VM you had. RAM was just a cache for your swap. So if you had alot of ram you needed at least that much swap behind it. From there it is pretty reasonable to go for double that, back in that era. Jason
Re: Swap space question
At the risk of being an AOL user, me too. The rule is "Make sure your real ram is at least a third of what you need", not "You need three times what you have". Regards, - Original Message - From: Michael Anthon <[EMAIL PROTECTED]> To: Sent: Tuesday, May 02, 2000 2:37 PM Subject: RE: Swap space question > > When I first installed Debian Sparc from the CD, I partitioned a Gig > > of Swap space since I have half a Gig of Ram. The Slink kernel would > > I have often seen this "rule of thumb" used in this way and I believe that > it has long been misinterpreted. The rule that I am talking about is "you > need at least twice the amount of swap space as you have RAM". > > I am pretty sure that the original interpretation of this rule was more > along the lines of "determine how much memory you will need to run > everything you need to run, then make sure that at least 1/3 of that is > physical RAM". > > The intention here is a trade off between system performance and cost. > Hardware has, however, progressed to a point where this rule is pretty much > useless for normal systems. If you are running a machine with 512M of RAM, > then you probably don't really need to configure any swap space at all > unless the machine will need it for running a big database or some other > memory hungry application. That 1G of swap space could be used for a much > better purpose (like storing 1G of pron or mp3s.. hehe). If you ever really > do need the extra memory, simple create a swap partition and use swapon as > the need arises. > > Just my $0.02 (+10%GST) worth. > > Regards > Michael Anthon > > > -- > To UNSUBSCRIBE, email to [EMAIL PROTECTED] > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED] > >
RE: Swap space question
> When I first installed Debian Sparc from the CD, I partitioned a Gig > of Swap space since I have half a Gig of Ram. The Slink kernel would I have often seen this "rule of thumb" used in this way and I believe that it has long been misinterpreted. The rule that I am talking about is "you need at least twice the amount of swap space as you have RAM". I am pretty sure that the original interpretation of this rule was more along the lines of "determine how much memory you will need to run everything you need to run, then make sure that at least 1/3 of that is physical RAM". The intention here is a trade off between system performance and cost. Hardware has, however, progressed to a point where this rule is pretty much useless for normal systems. If you are running a machine with 512M of RAM, then you probably don't really need to configure any swap space at all unless the machine will need it for running a big database or some other memory hungry application. That 1G of swap space could be used for a much better purpose (like storing 1G of pron or mp3s.. hehe). If you ever really do need the extra memory, simple create a swap partition and use swapon as the need arises. Just my $0.02 (+10%GST) worth. Regards Michael Anthon
