[nonameiguess]

I honestly don't think I like this at the application level. You're removing a degree of freedom from operators and users. I have a ton of memory on all of my home devices, and usually just take the working directories for frequently used applications and mount them as tmpfs. I do the same thing for application working directories of applications I deploy at work as well, where we have complete freedom to deploy memory-optimized servers with lots of RAM. Putting an extra in-memory cache on top of the OS filesystem that is already in-memory is an unnecessary extra step and doubling the memory use of each file that can't be turned off without patching and recompiling your application. The OS is already smart enough not to add a cache on top of tmpfs.

[haydnv]

I don't know that it's fair to say it's "doubling" the memory use of each file because the OS cache memory is still "free" from the perspective of an application. Where it comes in handy is an applications like databases or training an ML model where there are hot spots that get accessed/updated extremely frequently--then the application doesn't have to incur serialization overhead in order to read/write the data that the file encodes (although as another poster pointed out it might also be possible to do this with mmap).