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On 23 February 2006 14:04, jarry@×××.net wrote: |
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> "joaoemanuel1981" <joaoemanuel1981@×××××××.br> wrote: |
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> > Do i not understand why needs swap, if have 1GB of RAM? |
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> |
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> 1. because if you have 200GB disk, cutting 1 or 2GB for swap does not |
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> matter |
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True. |
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> |
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> 2. because someone told me some apps want to allocate swap no matter how |
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> ram you have (I think it was someone from hp-ux support, but I'm not sure |
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> if this is true for linux) |
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This is a myth. *No* application (under linux) can grab swap space directly. |
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Applications ask the kernel for memory when they allocate it. The kernel, |
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based on algorithms that balance free real ram, buffers and cache, returns |
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either real ram as memory to the app or - if it is low on real ram - swap |
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space. So what you do when adding swap space is extending your (fast) real |
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ram with (slow) memory residing on your harddrive. |
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> |
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> 3. because it is always better to have too much ram/swap then too little |
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Nnnnot always. There are circumstances when you do not want swap at all. |
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Consider a box that has certain real time response requirements which cannot |
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be met if apps are swapped out (actually parts of their code and/or data |
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paged out) to the harddrive. In these cases, you do not want swap but enough |
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ram to accommodate your running processes at all times. |
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This and 2. also mean that it's quite pointless to add swap if your |
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workstation has 16GB of ram and isn't used for image processing or other |
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extremely memory-hungry tasks. |
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> |
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> 4. because if you do not set up swap, but need it later, it will not be so |
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> easy to create it, if you partition all disk and leave no space left |
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The times when we couldn't resize partitions under linux without holding our |
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breath are over. |
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> |
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> 5. because it is a good *nix habit! :-) |
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What does or does not constitute good *nix habits is at least debateable. |
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If I needed a box that was fast at all times and (logical AND) money was of no |
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concern I'd put real ram in until the bugger stopped using swap space and |
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forget about swap. Since I do have to take monetary issues into |
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consideration, I rather configure some (cheap and slow) swap and have less |
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(expensive, compared to harddrive space, and fast) ram. How much ram and how |
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much swap is an economic question. |
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It all boils down to how and what for you use your box. If you need more |
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memory than you have ram, are you willing to invest the money for more ram? |
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No? Then you need swap. |
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There are too damn many myths about swap out there. Like this one: Always |
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configure twice as much swap as you have ram. Why? Why would I need more swap |
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if I increased my ram? You need at least a little bit of swap for peak memory |
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usage. Let's look at real numbers. Say, I am a bit low of ram for today's |
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computers. I have 256MB ram. For peak usage, I add 128MB swap. I open so many |
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applications/documents that the box starts swapping out 20MB. Sure, without |
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swap space, I wouldn't have been able to open the last document. But nothing |
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makes me stop there. I can as well run out of swap. |
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If you have 2GB of ram and 2GB of swap your total available memory is 4GB. If |
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you need more you have to add either ram or swap. What you add is your choice |
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based on your needs for speed and the money you are willing to spend on |
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memory. That's it. |
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End of rant. |
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Uwe |
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-- |
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Why do consumers keep buying products they will live to curse? |
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-- |
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