Debug builds of mongod check to see if our internal working set tracking is accurate, and display the message "warning: we think data is in ram but system says no" when our tracking code thinks that data is in RAM but the operating system's authoritative answer is that the data is not in RAM.
We use 'QueryWorkingSetEx()' on Windows and 'mincore()' on other OSes to see if a particular page is in RAM.
On Windows, the QueryWorkingSetEx API doesn't actually tell us what is in RAM; it tells us what is in RAM and on the "Working Set" list. Pages that are in RAM and are on the 'Standby' list are not reported by this API. The result is that Windows debug builds spew large quantities of these messages, making logs hard to use.
These events should be displayed less frequently.