On Tue, Aug 19, 2025 at 03:36:33PM +0100, John Garry wrote: > On 19/08/2025 14:39, Christoph Hellwig wrote: > > On Tue, Aug 19, 2025 at 12:42:01PM +0100, John Garry wrote: > > > nothing has been happening on this thread for a while. I figure that it is > > > because we have no good or obvious options. > > > > > > I think that it's better deal with the NVMe driver handling of AWUPF first, > > > as this applies to block fops as well. > > > > > > As for the suggestion to have an opt-in to use AWUPF, you wrote above that > > > users may not know when to enable this opt-in or not. > > > > > > It seems to me that we can give the option, but clearly label that it is > > > potentially dangerous. Hopefully the $RANDOMUSER with the $CHEAPO SSD will > > > be wise and steer clear. > > > > > > If we always ignore AWUPF, I fear that lots of sound NVMe implementations > > > will be excluded from HW atomics. > > > > I think ignoring AWUPF is a good idea, but I've also hard some folks > > not liking that. > > Disabling reading AWUPF would be the best way to know that for sure :) What is the likelihood of convincing the nvme standards folks to add a new command for write-untorn that doesn't just silently fail if you get the parameters wrong? > > The reason why I prefer a mount option is because we add that to fstab > > and the kernel command line easily. For block layer or driver options > > we'd either need a sysfs file which is always annoying to apply at boot > > time, (Yuck, mount options, look how poorly that went for dax= ;)) > Could system-udev auto enable for us via sysfs file or ioctl? Userspace controllable sysfs configuration knobs like discard_max_bytes and discard_max_hw_bytes work well with that model. The nvme layer can set atomic_write_bytes to zero by default, and a udev rule can change it up to atomic_write_max_hw_bytes. That's not /so/ bad if you can either get the udev rulefile merged into systemd, or dropped in via clod-init or something. --D > > or a module option which has the downside of applying to all > > devices. > > About the mount option, I suppose that it won't do much harm - it's just a > bit of extra work to configure. > > I just fear that admins will miss enabling it or not enable it out of doubt > and users won't see the benefit of HW atomics. > > >
