The activity factor, , is obtained by
dividing the number of memory transactions by the maximum possible
number of memory transactions during non-idle time, .
The dividend is obtained
from performance monitoring registers available on most modern
processors, and the divisor is derived from the memory device's
datasheet.
Note that due to
limitations in older ISA hardware, Linux for x86 already has support to
limit DMA transactions to the first 16 MB of memory (i.e., within the
first node).