man/io_uring_register_buffers.3: mention why registered buffers are useful
There are no details in this man page, so mention why it is in fact
beneficial to register buffers. This is specific to O_DIRECT file IO
for now, but the kernel side use cases will be expanded in the future.
@@ -26,9 +26,16 @@ belonging to the
After the caller has registered the buffers, they can be used with one of the
fixed buffers functions.
+Registered buffers is an optimization that is useful in conjunction with
+.B O_DIRECT
+reads and writes, where maps the specified range into the kernel once when
+the buffer is registered, rather than doing a map and unmap for each IO
+every time IO is performed to that region. Additionally, it also avoids
+manipulating the page reference counts for each IO.
+
.SH RETURN VALUE
On success
.BR io_uring_register_buffers (3)
returns 0. On failure it returns -errno.
.SH SEE ALSO
-.BR io_uring_get_sqe (3), io_uring_unregister_buffers (3)
\ No newline at end of file
+.BR io_uring_get_sqe (3), io_uring_unregister_buffers (3), io_uring_prep_read_fixed (3), io_uring_prep_write_fixed (3)
