I am not sure if you mean what you have written, or you mean the opposite, but reading a big file when there are no available free memory pages will flush memory pages from the disk cache, which previously were caching data from files accessed by your user, or by other users.

In high performance applications, you must not let the kernel choose randomly what pages should be invalidated, but you must use madvise for memory_mapped files or posix_fadvise for files accessed with read/write, with appropriate arguments so that cache memory pages that are not needed any more will be freed with enough time in advance before reading more data.