With a hot cache, your disk is only going to do writes (and waiting on those writes is the reason why they suggest a make -jN with N higher than the number of c

With a hot cache, your disk is only going to do writes (and waiting on those writes is the reason why they suggest a make -jN with N higher than the number of cores). All reads are going to be serviced from memory. All writes will also go to the cache and will be coalesced on close().