How to cache external Javascript files?

In Linux, is it possible to mmap() a file in such a way that it will never be swapped out to a disk in favor of files which, using the normal read(), have been placed into the page/buffer cache?

• If not using mmap(), it seems like there should be a way to give certain files "priority", so that the only time they're swapped out is for page faults trying to bring in, e.g., executing code, or memory that was malloc()'d by some process. One can think of situations where this could be useful. Consider search engines, which should keep their index files in cache. EDIT: Specifically, the mmap()'d file should still be pageable, just not in favor of other files. In the example, the search index files could be enormous, so using mlock() is out of the question unfortunately.

• Answer:

  There is an mlock(2) call for this specific purpose: to lock region of memory into physical memory. See [1] Second, to lock something into memory, it has to be a virtual memory region. It must be allocated by mmap, malloc or similar calls, but not read(2). Read(2) requires a pre-allocated memory region to be passed in, which is either malloc-ed / mmap-ed, or automatically allocated on the stack. [1] http://man7.org/linux/man-pages/man2/mlock.2.html