When memory is frequently accessed, it's put onto the CPU cache (L1, L2, L3). However, is the same true of memory that is mmap'd to a file living in /dev/shm? I ask because I wanted to know if having it backed to a file in /dev/shm would bypass any kind of caching by the CPU, and rather letting it fall through to a cache miss.
Yes they'll be cached in the core's L1/L2/L3 caches unless for instance the pages are marked uncached (e.g., by configuring the PAT accordingly) or the data is accessed via streaming reads/writes.