On Tue 07-01-20 10:49:55, Dan Williams wrote: > On Tue, Jan 7, 2020 at 10:33 AM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > W.r.t partitioning, bdev_dax_pgoff() seems to be the pain point where > > dax code refers back to block device to figure out partition offset in > > dax device. If we create a dax object corresponding to "struct block_device" > > and store sector offset in that, then we could pass that object to dax > > code and not worry about referring back to bdev. I have written some > > proof of concept code and called that object "dax_handle". I can post > > that code if there is interest. > > I don't think it's worth it in the end especially considering > filesystems are looking to operate on /dev/dax devices directly and > remove block entanglements entirely. > > > IMHO, it feels useful to be able to partition and use a dax capable > > block device in same way as non-dax block device. It will be really > > odd to think that if filesystem is on /dev/pmem0p1, then dax can't > > be enabled but if filesystem is on /dev/mapper/pmem0p1, then dax > > will work. > > That can already happen today. If you do not properly align the > partition then dax operations will be disabled. This proposal just > extends that existing failure domain to make all partitions fail to > support dax. Well, I have some sympathy with the sysadmin that has /dev/pmem0 device, decides to create partitions on it for whatever (possibly misguided) reason and then ponders why the hell DAX is not working? And PAGE_SIZE partition alignment is so obvious and widespread that I don't count it as a realistic error case sysadmins would be pondering about currently. So I'd find two options reasonably consistent: 1) Keep status quo where partitions are created and support DAX. 2) Stop partition creation altogether, if anyones wants to split pmem device further, he can use dm-linear for that (i.e., kpartx). But I'm not sure if the ship hasn't already sailed for option 2) to be feasible without angry users and Linus reverting the change. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
