Consider POSIX_FADV_NOREUSE?

[Ronan Pigott]

Hey rsync,

Seems like there was an effort a while back to make use of POSIX_FADV_DONTNEED
on linux [1]. Though the linux patches landed, apparently the rsync ones never
did.

Over a decade later we live in a different world. Linux is using the new-ish
MGLRU on many distros, and (~6.3+) even has support for POSIX_FADV_NOREUSE [2],
which was dismissed in prior discussions for lack of support.

Maybe it's time to re-evaluate the utility of posix_fadvise in rsync?

[1] https://lkml.org/lkml/2010/11/21/59
[2] https://lore.kernel.org/all/20221230215252.2628425-2-yuzhao@google.com/T/#u

Cheers,
Ronan