Swap questions

[Shoshana Abrass]

  I've been playing around with osview, trying to determine the optimal
  swap space for a PI with 48 to 64 Mbytes of memory. I noticed a few
  oddities, and I'm hoping someone at SGI can explain them.

  First, the reason we have so much memory is that we manipulate large
  image files (1-16 Mb), several at a time. But even on a machine that's
  manipulating 16 Mb files, swap activity seems very low. "swap -l"
  claims that only 5 Mb of swap are being used. "osview -i1" shows lots
  of page faults, but hardly any swapping activity. So my questions are:

  1. Are the image files ever paged out to the swap area? it seems not.
	 It seems like the executable code is the only thing getting paged
	 to virtual memory.

  2. Are the image files 'swapin'ed (according to osview) when they're 
	 first read into memory? What's the difference between the "Virtual
	 Memory" and "Swap" in osview?

  In a kernel class I took, the instructor claimed that whenever a process
  was read into memory, swap space was reserved/allocated for it, before 
  it ever got paged out. Is this true under Irix? (is it ever true, for 
  that matter). If this is true, it implies that one must have at least
  as much swap as real memory... even though "swap -l" claims that no
  swap is being used. Also, if it is true, is it only true for the 
  executable code, and not the data?

  What's the real scoop here? Any help much appreciated.

  -shoshana
  pdi!shoshana at sgi.com

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