On Fri, Dec 17, 2021 at 10:48:22AM +1100, NeilBrown wrote: > Linux primarily uses IO to block devices for swap, but can send the IO > requests to a filesystem. This has only ever worked for NFS, and that > hasn't worked for a while due to a lack of testing. This seems like a > good time for some tidy-up before restoring swap-over-NFS functionality. The changes look good to me, but I think this needs to be split into separate, self-contained patches. > > This patch: Patch 1: > - updates the documentation (both copies!) for swap_activate which > is woefully out-of-date Patch 2: > - drops the call to the filesystem for ->set_page_dirty(). These > pages do not belong to the filesystem, and it has no interest > in the dirty status. Patch 3: > - move the responsibility for setting SWP_FS_OPS to ->swap_activate() > and also requires it to always call add_swap_extent(). This makes > it much easier to find filesystems that require SWP_FS_OPS. Patch 4: > - introduces a new address_space operation "swap_rw" for swap IO. > The code currently used ->readpage for reads and ->direct_IO for > writes. The former imposes a limit of one-page-at-a-time, the > later means that direct writes and swap writes are encouraged to > use the same path. While similar, swap can often be simpler as > it can assume that no allocation is needed, and coherence with the > page cache is irrelevant.
