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DateFri, 17 Jan 1997 13:36:03 -0400 (AST)
FromWilliam Burrow <>
SubjectRe: Swapped out truly zero pages & big scientific calculations
On Thu, 16 Jan 1997, Mark Hemment wrote:

> > mingo wrote:> > This minipatch is for making statistics about how many truly zero
> > content (but otherwise totally private mapped) pages are swapped
> > out in the system. As it has to check for every page swapped out
> > wether it's zero or not, it slows down swapping ... it's really
> > just for making statistics.> > I like this, I'll try and get some stats on my box.
> I believe it's not going to slow down paging out to swap by a
> noticable amount, and if a zero page is found it can be added to the
> pool of zero pages...

To find out what impact the check might have on swapping non-zero pages,
you might keep track of when a non-zero page is detected.  I believe that
most non-zero pages have non-zero data at the beginning.  To test this
hypothesis, just a another counter to the stats whenever the value of i in
mingo's patch is below a certain value (8 test loops would suit my guess). 
The code would look something like: 

       if (!i)
          kstat.zero++
       elif (i > (PAGE_SIZE/sizeof(unsigned long int))
          kstat.nonzero++
or what have you. 

--
William Burrow  --  Fredericton Area Network, New Brunswick, Canada
Copyright 1997 William Burrow  
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