Messages in this thread | | | Date | Wed, 26 May 2004 12:58:37 +0200 | From | Matthias Schniedermeyer <> | Subject | Re: why swap at all? |
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On Wed, May 26, 2004 at 08:33:28PM +1000, Nick Piggin wrote: > Matthias Schniedermeyer wrote: > >On Wed, May 26, 2004 at 07:48:10PM +1000, Nick Piggin wrote: > > > >>John Bradford wrote: > >> > >>>Quote from Nick Piggin <nickpiggin@yahoo.com.au>: > >>> > >>> > >>>>Even for systems that don't *need* the extra memory space, swap can > >>>>actually provide performance improvements by allowing unused memory > >>>>to be replaced with often-used memory. > >>> > >>> > >>>That's true, but it's not a magical property of swap space - extra > >>>physical > >>>RAM would do more or less the same thing. > >>> > >> > >>Well it is a magical property of swap space, because extra RAM > >>doesn't allow you to replace unused memory with often used memory. > >> > >>The theory holds true no matter how much RAM you have. Swap can > >>improve performance. It can be trivially demonstrated. > > > > > >The other way around can be "demonstrated" equally trivially. > > > >In my personal machine i have 3GB of RAM and i regularly create > >DVD-ISO-Images (about 2 per day). After creating an image (reading up to > >4,4GB and writing up to 4,4GB) the cache is 100% trashed(1). With swap > >it would be even more trashed then it is without swap(1). > > > > I don't disagree that you could find a situation where swap > is worse than no swap. I don't understand what you mean by > trashed and more trashed though :)
trashed means "everything i need(tm)" is paged out (mozilla/konsole/xine ...)
with swap the data-part of running programs was swapped out, without swap only the program-part is thrown out of memory as the data-part can't be moved anywhere else.
I have a 10KPRM SCSI-HDD, i can here what my system is doing. :-)
> Creating your ISOs makes your system swap a lot when swap > is enabled?
Transfering up to 8,8GB tends to trash the cache.
> >1: This has "always(tm)" been so since i began burning DVDs 3 years ago. > >Beginning from kernel 2.4.4-2.4.25 and 2.6.4-2.6.6. Currently i use 2.6.5. > >(This is no typo!) > > > >I have only tested the "with swap"-case with 2.4.4 as i didn't use swap > >after 2.4.4 trashed so badly with swap enabled. But i don't think that > >things have changed so fundamentaly that the "with swap"-case is > >better(FOR ME!) than the "without swap"-case. > > > > The 2.6 VM has changed pretty fundamentally. It would be good > if you could retest.
Bis denn
-- Real Programmers consider "what you see is what you get" to be just as bad a concept in Text Editors as it is in women. No, the Real Programmer wants a "you asked for it, you got it" text editor -- complicated, cryptic, powerful, unforgiving, dangerous.
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