On Fri, Aug 13, 2021 at 04:09:39AM +0100, Matthew Wilcox wrote:

On Thu, Aug 12, 2021 at 09:22:06PM +0100, David Howells wrote:

quoted

Trying to use a swapfile on NFS results in every DIO write failing with
ETXTBSY because generic_write_checks(), as called by nfs_direct_write()
from nfs_direct_IO(), forbids writes to swapfiles.

Why does nfs_direct_write() call generic_write_checks()?

ie call generic_write_checks() earlier, and only swap would bypass them.

Yes, something like that is a good idea probably.  Additionally I'd like
to move to a separate of for swap I/O ASAP given that NFS only
implemens ->direct_IO for swap.