/usr/share/vim/vim74/spell/spell.vim is in vim-runtime 2:7.4.052-1ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | " Settings for when generating spellfiles.
"
" Assume we have 2 Gbyte RAM available.
set mkspellmem=1800000,6000,1600
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