Swappiness and Virtual Memory Management

[Ow Mun Heng]

On Wed, 2005-04-27 at 23:19 -0400, Peter Arremann wrote:
> On Wednesday 27 April 2005 23:06, Ow Mun Heng wrote:
> > Yes.. this is on a laptop with a 5400rpm drive. Though I know that it is
> > an issue, the friend running on FreeBSD on a thinkpad X40 doesn't see
> > this issue when getting > 700MB in swap. If I hit like 200MB in swap,
> > I'm already thrashing. Moving from Evo to Firefox is a wait as it swaps
> > in/out.

> Are they doing similar work? Same apps and all? how big is the memory 
> footprint of the same app on the different OSes? What applications are you 
> runnin

Not too sure on that since the laptop's not mine.. but still gonna be
the same apps such as Evo and Firefox acroread etc...

Evo on my laptop is already 150MB

> 
> > > Other than that, yes FreeBSD I can agree acts a little nicer when it
> > > comes to swapping - but in all honesty, the difference is so little that
> > > you really have to test the system and create the swapping on purpose and
> > > then time the apps to notice any difference.
> >
> > How much that is true I can't tell but what I do know is the difference
> > is noticeable in the sense of the word. It just feels slower on Linux
> > rather than on BSD.
> >
> > I've seen one other poster that mentioned it's cause linux pushes around
> > 4k for every read of the swap and thus makes things slower.

> Paging is CPU dependent. the CPU contains a memory management unit (MMU) that 
> is responsible for deciding which page (hence the name paging) is where in 
> main memory or if it is not available. 

Both laptops are 1.4G Pentium M

> If a page is requested that is not 
> currently in memory a trap occurs, the OS paging process is invoked and it 
> loads the correct page... Then there is a process that marks pages to be 
> paged out and if you try to allocate memory and are below the min free (or 
> your OSes equiv of that variable) then some pages are written to disk (data) 
> or are simply discarded (executables). 
> Either way, the page size is the same - 4k or 4m on i386, 8k on traditional 
> sparc... hardware, not OS dependent. 
> 
> Peter.
> 

-- 
Ow Mun Heng
Gentoo/Linux on DELL D600 1.4Ghz 
98% Microsoft(tm) Free!! 
Neuromancer 12:00:57 up 2 days, 2:41, 5 users, load average: 0.23, 0.27,
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