If by kernel you mean linux, then yes, it does do precisely that. Try this out on a large file: time cat bigfile > /dev/null time cat bigfire > /dev/nul

If by kernel you mean linux, then yes, it does do precisely that. Try this out on a large file: time cat bigfile > /dev/null time cat bigfire > /dev/null Then wait a few minutes and try again. Linux won't evict the pages from the cache unless something else wants to use the space.