large pages (amd64)

[Wojciech Puchar]

i enabled
vm.pmap.pg_ps_enabled: 1


could you please explain what exactly this values means?
because i don't understand why promotions-demotions!=mappings

vm.pmap.pde.promotions: 2703
vm.pmap.pde.p_failures: 6290
vm.pmap.pde.mappings: 610
vm.pmap.pde.demotions: 289




other question - tried enabling it on my i386 laptop (256 megs ram), 
always mappings==0, while promitions>demotions>0.

certainly there are apps that could be put on big pages, gimp editing 40MB 
bitmap for example