On Fri 05-05-23 09:07:36, Dave Chinner wrote: > 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. Yeah, I'm fine with this behavior. I just wasn't sure whether Ilya didn't need the sysfs change to be visible in the filesystem so that was why I pointed that out. But apparently he doesn't need it. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
