On Wed, Apr 10, 2024 at 05:05:20AM +0100, Matthew Wilcox wrote: > On Mon, Apr 08, 2024 at 10:50:47AM -0700, Luis Chamberlain wrote: > > On Fri, Apr 05, 2024 at 11:06:00AM +0100, John Garry wrote: > > > On 04/04/2024 17:48, Matthew Wilcox wrote: > > > > > > The thing is that there's no requirement for an interface as complex as > > > > > > the one you're proposing here. I've talked to a few database people > > > > > > and all they want is to increase the untorn write boundary from "one > > > > > > disc block" to one database block, typically 8kB or 16kB. > > > > > > > > > > > > So they would be quite happy with a much simpler interface where they > > > > > > set the inode block size at inode creation time, > > > > > We want to support untorn writes for bdev file operations - how can we set > > > > > the inode block size there? Currently it is based on logical block size. > > > > ioctl(BLKBSZSET), I guess? That currently limits to PAGE_SIZE, but I > > > > think we can remove that limitation with the bs>PS patches. > > > > I can say a bit more on this, as I explored that. Essentially Matthew, > > yes, I got that to work but it requires a set of different patches. We have > > what we tried and then based on feedback from Chinner we have a > > direction on what to try next. The last effort on that front was having the > > iomap aops for bdev be used and lifting the PAGE_SIZE limit up to the > > page cache limits. The crux on that front was that we end requiring > > disabling BUFFER_HEAD and that is pretty limitting, so my old > > implementation had dynamic aops so to let us use the buffer-head aops > > only when using filesystems which require it and use iomap aops > > otherwise. But as Chinner noted we learned through the DAX experience > > that's not a route we want to again try, so the real solution is to > > extend iomap bdev aops code with buffer-head compatibility. > > Have you tried just using the buffer_head code? I think you heard bad > advice at last LSFMM. Since then I've landed a bunch of patches which > remove PAGE_SIZE assumptions throughout the buffer_head code, and while > I haven't tried it, it might work. And it might be easier to make work > than adding more BH hacks to the iomap code. I have considered it but the issue is that *may work* isn't good enough and without a test plan for buffer-heads on a real filesystem this may never suffice. Addressing a buffere-head iomap compat for the block device cache is less error prone here for now. Luis
