QtMoko Virtual Memory

David Garabana Barro david at garabana.com
Wed Sep 1 12:38:15 CEST 2010

On Miércoles, 1 de Septiembre de 2010 11:22:45 Gennady Kupava escribió:
> В Срд, 01/09/2010 в 10:50 +0200, Nashvin Gangaram пишет:
> >       * Does swap cause a significant performance increase with
> >       
> >         QtMoko?
> No, i think it may cause significant performance decrease instead. But
> this just educated guess and it would be better to do some testing to
> prove this.

It's not true for me, and it's a common misunderstanding IMHO. 

For testing, simply try to download tiles at zoom level 11, for the upper 6 
zoom levels in tangoGPS. Better if you make it twice (moving on the map)

Without swap, it will catch all available memory, and FR will get really 
slooooow, to the limit of appearing to hang, and even sometimes oomkill will 
start killing some random process.
With swap, linux can swap unused pages (other daemon pages, not tangogps ones) 
and tangogps will continue running, and FR will be responsible. You only will 
notice some 1-4 seconds slowdown from time to time, when pages are swapped out

swap is not only for "creating" more memory. If FR starts to massively trashing 
pages to swap, it will really SLOW things a lot, for sure (the same is true for 
your PC)

But it will help *a lot* to have more memory available for running apps.
Think on swap as a place where put unused memory pages, and use real RAM for 
currently used apps or caching files from slow uSD

Swap will *ALLWAYS* help, but will help a lot more on a limited memory device, 
as FR

Here [1] you can read more about what I'm saying.

[1] http://kerneltrap.org/node/3202
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