On Thu, May 04, 2023 at 05:16:48PM +0100, Matthew Wilcox wrote: > On Thu, May 04, 2023 at 05:55:56PM +0200, Jan Kara wrote: > > For bdev address_space that's easy but what Ilya also mentioned is a > > problem when 'stable_write' flag gets toggled on the device and in that > > case having to propagate the flag update to all the address_space > > structures is a nightmare... > > We have a number of flags which don't take effect when modified on a > block device with a mounted filesystem on it. For example, modifying > the readahead settings do not change existing files, only new ones. > Since this flag is only modifiable for debugging purposes, I think I'm > OK with it not affecting already-mounted filesystems. It feels like a > decision that reasonable people could disagree on, though. I think an address space flag makes sense, because then we don't even have to care about the special bdev sb/inode thing - folio->mapping will already point at the bdev mapping and so do the right thing. That is, if the bdev changes stable_write state, it can toggle the AS_STABLE_WRITE flag on it's inode->i_mapping straight away and all the folios and files pointing to the bdev mapping will change behaviour immediately. Everything else retains the same behaviour we have now - the stable_write state is persistent on the superblock until the filesystem mount is cycled. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
