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Re: [TEKNIK] Samle to partitioner



Thue Janus Kristensen wrote:
2009/10/25 Jørgen Heesche <sslug@sslug>

Martin Møller Skarbiniks Pedersen wrote:

2009/10/25 Jørgen Heesche <sslug@sslug>:

 Swapstørrelse skal mindst være lig med RAM, så sæt 1Gb til swap; det er
nok,
hvis der ikke skal køre tunge jobs.

Hvorfor nu det ?
Faktisk virker linux også fint uden swap.


Ja tilsyneladende, men hvis man har store applikationer kan en stor portion
RAM være inaktiv i lang tid. En applikation allokerer ved opstart så meget
RAM som muligt, men al den RAM er ikke aktiv hele tiden. Hvis ikke det er
muligt at swappe vil der altså være et spild af resourcer, hvilket kan
forhindre samtidig kørsel af andre applikatioer.


Det vil vel kun forhindre andre applikationer i at køre i ekstreme
brugs-tilfælde. Men det eksempel du nævner vil betyde at kernel vil være
tvunget til mere aktivt at rydde disk-cachen for diverse cachede filer og
cachet programkode, når det ville være smartere at swappe allokeret
hukommelse ud hvis der var noget swap-space, hvilket vil gøre systemet
langsommere.

(Jeg er ikke på nogen måde ekspert, men jeg ville bare lige nævne de
åbenlyse konsekvenser jeg umiddelbart kunne se)

Jeg er heller ikke ekspert.
Jeg har fundet dette:
http://kerneltrap.org/node/16317
Has swap still a use with 4 GB of memory?

Swap lets you exchange rarely used memory for commonly used memory. If you start a large app, use it for a while to get it grab some memory and then leave it running it is consuming resources. If you have no swap it will continue to use ram for as long as it is left running. This would be days, weeks or months. If you have swap the system will notice the app is not in use and will swap it out allowing for the memory to be reused as disk cache. Disk caching improves overall performance. So there is a performance hit when the app is swapped out (and potentially swapped back in) and there is a performance gain due to the use of disk cache. Except in usual usage patterns the rate of cache hits will be high enough to make this a significant win.

Bemærk:
Disk caching improves overall performance. So there is a performance hit when the app is swapped out (and potentially swapped back in) and there is a performance gain due to the use of disk cache.

--
Med venlig hilsen

Jørgen Heesche
mailto:sslug@sslug


 
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