On Fri 08-09-17 11:39:13, Ted Tso wrote: > On Fri, Sep 08, 2017 at 09:25:43AM +1000, Dave Chinner wrote: > > > Okay, so other ideas (which you have also probably already though of) include: > > > > > > 1) Just return -EBUSY if anyone tries to change the DAX flag of an inode with > > > open mappings or any open file handles. > > > > You have to have an open fd to change the flag. :) > > What if we only allow the S_DAX flag to be *set*, when i_size and > i_blocks is zero? We could also require that only one file descriptor > be open against the inode, and that it be opened O_RDONLY. We could do something like that but IMHO it will be a pain to use (e.g. think how difficult it would be to switch your existing database to use DAX for data files). We can make transition reliable whenever inode->i_mapping->i_mmap RB tree is empty (effectively: whenever the file is not mmaped). And that should be relaxed enough for most usecases... But I agree that it will be somewhat tricky to prevent creation of new mappings while we are switching S_DAX flag so it needs more though. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
