fs: Avoid predictable page faults for sys_write() user buffer pages
Introduce a new fault_in_iov_iter_slow_readable() helper for faulting in
an iterator via get_user_pages() instead of triggering page faults.
This is slower than a simple memory read when the underlying pages are
resident, but avoids the page fault overhead when the underlying pages
need to be faulted in.
Use fault_in_iov_iter_slow_readable() in generic_perform_write and
iomap_write_iter when reading from the user buffer fails.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
6 files changed
