On Thu, May 03, 2018 at 01:58:03PM -0700, Omar Sandoval wrote: > On Thu, May 03, 2018 at 10:46:59AM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > > > Add a new iomap_swapfile_activate function so that filesystems can > > activate swap files without having to use the obsolete and slow bmap > > function. This enables XFS to support fallocate'd swap files and > > swap files on realtime devices. > > > > Shouldn't we also prevent the extents of an active swapfile from > becoming shared? If I swapon(a) and reflink(a, b), swapout to a now has > to break the reflink or corrupt b! In my old Btrfs swapfile series [1] I > just forbid all reflink operations on active swapfiles. xfs already does this in its reflink handler: it takes the inode lock & bails out if IS_SWAPFILE(). swapon calls claim_swapfile to take the inode lock and sets S_SWAPFILE (if successful) so the two are effectively locked out from each other... > One thing to note is that then this will need a matching > ->swap_deactivate(), which currently isn't called if ->swap_activate() > returned > 0. ...so there shouldn't be any state to undo if the iomap_swapfile_activate fails. --D > > 1: https://github.com/osandov/linux/tree/btrfs-swap > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > --- > > v3: catch null iomap addr, fix too-short extent detection > > v2: document the swap file layout requirements, combine adjacent > > real/unwritten extents, align reported swap extents to physical page > > size boundaries, fix compiler errors when swap disabled
