On Mon, Mar 19, 2018 at 11:19 AM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > On Mon, Mar 19, 2018 at 10:57:55AM -0700, Dan Williams wrote: >> On Mon, Mar 19, 2018 at 10:33 AM, Darrick J. Wong >> <darrick.wong@xxxxxxxxxx> wrote: >> > On Thu, Mar 15, 2018 at 08:52:29AM -0700, Dan Williams wrote: >> >> In preparation for adding coordination between truncate operations and >> >> busy dax-pages, extend xfs_break_layouts() to assume it must be called >> >> with the mmap lock held. This locking scheme will be required for >> >> coordinating the break of 'dax layouts' (non-idle dax (ZONE_DEVICE) >> >> pages mapped into the file's address space). >> > >> > If I'm reading this right, you've added a requirement (for xfs anyway) >> > that we have to have grabbed MMAPLOCK_EXCL before calling break_layout() >> > so that the layout breaking process will block until active dmas have >> > finished. >> > >> > In 4.16 we added xfs_iolock_two_inodes_and_break_layout (in >> > xfs_reflink.c) to break pnfs leases for files that are about to be >> > reflinked (since pnfs and reflink aren't compatible either). I think >> > that function will have to be adapted to take the appropriate mmap locks >> > too -- definitely the exclusive mmap lock for the destination file >> > because we anticipate punching out blocks. I'm not sure about the >> > source file; I think taking the shared mmap lock is fine for that? >> >> I don't see anything to adapt with respect to mmap locks since reflink >> and dax are mutually exclusive. The new lock coordination and layout >> breaking in xfs_break_dax_layouts() only applies to dax vs truncate, >> so xfs_iolock_two_inodes_and_break_layout() looks ok to me as is. > > I was aiming for DAX + reflink someday working together. :) Of course, but then fixing up xfs_iolock_two_inodes_and_break_layout() is a follow on consideration from this patch series. > As far as that goes, I think the only thing we really have to do is > figure out how to make iomap_begin do the cow operation before letting > userspace write to (or MAP_SYNC a writable region) pmem, right? Yes, I think so, trigger xfs_break_dax_layouts() on the destination inode on any write fault.
