Description:

The nocache tool tries to minimize the effect an application has on
the Linux file system cache. This is done by intercepting the open and
close system calls and calling posix_fadvise with the
POSIX_FADV_DONTNEED parameter. Because the library remembers which
pages (ie., 4K-blocks of the file) were already in file system cache
when the file was opened, these will not be marked as "don't need",
because other applications might need that, although they are not
actively used (think: hot standby).

Use case: backup processes that should not interfere with the present
state of the cache.