Host pages include two memory-related metrics for your hosts, Memory used and Page faults. Both measurements and other factors, are used to correlate and calculate host high memory incidents.
Percentage of total RAM used by processes. RAM used by system caches and buffers isn't included in this metric. Dynatrace calculates memory usage as:
memory_used = total_memory_size - (free_memory + active_memory + inactive_memory + reclaimamble_memory)
for your picture, the value of memory depends on the selected time period