adjusting lowmem_reserve_ratio on an embedded system?

[Daniel Kabs <daniel.kabs@gmx.de>]

Hello,

in tracing a low on memory situation on an embedded system I came across 
the Documentation/sysctl/vm.txt. There it is advised to change the 
lowmem_reserve_ratio on systems running without swap.

I wonder if this applies for an embedded system running with 256MByte RAM 
and no swap which is using only one memory zone (ZONE_NORMAL)? I guess 
no.


To understand what the parameter means I read the relevant section from 
vm.txt and came across the terms "lowmem zone" and "lower zones" 
and "lowmem memory". I feel dumb. I could not find a concept of "lower 
zones" (or "upper" zones).  What exactly do they mean?

Cheers
Daniel