Actually there is no dphys-swapfile program on a default Ubuntu installation CD and it is not used to calculate the swap size.

What happens is that the ubiquity installer uses the partman-auto scripts and configuration files (called recipes) to determine the sizes of all partitions. It works like this:

• Partman finds the right recipe file according to the type of the computer and the option the user has chosen.


• There it finds the minimum and maximum size of the partition and its priority. For swap it can be 96 (min - in MB) 512 (priority) 300% (max).


• Then it gets the RAM size (via /proc/meminfo).


• It uses its own algorithm to calculate the sizes.

Details:

A recipe file can look like this:

1 1 1 free

    $iflabel{ gpt }

    method{ biosgrub } .



500 10000 -1 $default_filesystem

    $lvmok{ }

    method{ format }

    format{ }

    mountpoint{ / } .



96 512 300% linux-swap

    $lvmok{ }

    method{ swap }

    format{ } .

The algorithm to calculate the sizes:

for(i=1;i<=N;i++) {

   factor[i] = priority[i] - min[i];

}

ready = FALSE;

while (! ready) {

   minsum = min[1] + min[2] + ... + min[N];

   factsum = factor[1] + factor[2] + ... + factor[N];

   ready = TRUE;

   for(i=1;i<=N;i++) {

      x = min[i] + (free_space - minsum) * factor[i] / factsum;

      if (x > max[i])

         x = max[i];

      if (x != min[i]) {

         ready = FALSE;

         min[i] = x;

      }

   }

}

For more see:

• partman-auto-recipe.txt^{Way Back Machine}




• http://dev.blankonlinux.or.id/browser/pattimura/ubiquity/d-i/source/partman-auto/lib/recipes.sh?rev=pattimura%2Cubiquity%2C261 ^{DEAD LINK}