On Tue 25-08-20 13:16:16, Christoph Hellwig wrote: > On Tue, Aug 25, 2020 at 02:05:54PM +0200, Jan Kara wrote: > > Discarding blocks and buffers under a mounted filesystem is hardly > > anything admin wants to do. Usually it will confuse the filesystem and > > sometimes the loss of buffer_head state (including b_private field) can > > even cause crashes like: > > Doesn't work if the file system uses multiple devices. Hum, right. > I think we just really need to split the fs buffer_head address space > from the block device one. Everything else is just going to cause a huge > mess. 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? 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). So we would need to somehow maintain at least vague coherence between these caches which would be ugly. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
