Messages in this thread | | | Date | Wed, 26 May 2004 11:00:39 +0200 | From | Helge Hafting <> | Subject | Re: why swap at all? |
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Anthony DiSante wrote:
> As a general question about ram/swap and relating to some of the > issues in this thread: > > ~500 megs cached yet 2.6.5 goes into swap hell > > Consider this: I have a desktop system with 256MB ram, so I make a > 256MB swap partition. So I have 512MB "memory" and if some process > wants more, too bad, there is no more. > > Now I buy another 256MB of ram, so I have 512MB of real memory. Why > not just disable my swap completely now? I won't have increased my > memory's size at all, but won't I have increased its performance lots?
This is correct. You now have 512M of fast memory instead of 256M fast memory and 256M "slow" memory. You don't _need_ to have additional swap, but it is usually a good idea. If you keep your 256M of swap, then you now have 512M fast memory + 256M slow memory for a total of 768M. This is even better.
Please note that your machine _will_ do one kind of swapping even if you don't configure any swap: Executable files are a kind of swap-files, if memory pressure happens then (part of) your programs will be evicted from memory _because_ they can be reloaded from their executables.
This cause the same sort of performance degradations as swapping to a swap partition. Actually, it is worse because swapping to a swap partition allows swapping out little-used writeable memory before discarding program code that might see more use. So if swapping happens, then you're better off with a swap partition because then it is the least used stuff that goes first. Without a swap partition, the least used program code goes, but it may or may not be the least used memory overall.
Helge Hafting
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