On Thu, Aug 27, 2020 at 10:39:00PM +0100, Al Viro wrote: > On Thu, Aug 27, 2020 at 08:16:03AM +0100, Christoph Hellwig wrote: > > On Tue, Aug 25, 2020 at 04:50:56PM +0200, Jan Kara wrote: > > > Do you mean that address_space filesystem uses to access its metadata on > > > /dev/sda will be different from the address_space you will see when reading > > > say /dev/sda? Thus these will be completely separate (and incoherent) > > > caches? > > > > Yes. > > > > > Although this would be simple it will break userspace I'm afraid. > > > There are situations where tools read e.g. superblock of a mounted > > > filesystem from the block device and rely on the data to be reasonably > > > recent. Even worse e.g. tune2fs or e2fsck can *modify* superblock of a > > > mounted filesystem through the block device (e.g. to set 'fsck after X > > > mounts' fields and similar). > > > > We've not had any problems when XFS stopped using the block device > > address space 9.5 years ago. > > How much writes from fsck use does xfs see, again? All of them, because xfs_repair uses direct IO and caches what it needs in userspace. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
