On Thu, Jul 15, 2021 at 02:01:11PM -0400, Josef Bacik wrote: > The problem I ran into was the automount stuff requires that we have a > completely different superblock for every vfsmount. This is fine for > things like nfs or samba where the automount literally points to a > completely different mount, but doesn't work for btrfs where it's on > the same file system. If you have 1000 subvolumes and run sync() > you're going to write the superblock 1000 times for the same file > system. Dumb question: why do you have to write the superblock 1000 times, and why is that slower than writing to 1000 different filesystems? > You are > going to reclaim inodes on the same file system 1000 times. You are > going to reclaim dcache on the same filesytem 1000 times. You are > also going to pin 1000 dentries/inodes into memory whenever you > wander into these things because the super is going to hold them > open. That last part at least is the same for the 1000-different-filesystems case, isn't it? --b. > This is not a workable solution. It's not a matter of simply tying > into existing infrastructure, we'd have to completely rework how the > VFS deals with this stuff in order to be reasonable. And when I > brought this up to Al he told me I was insane and we absolutely had > to have a different SB for every vfsmount, which means we can't use > vfsmount for this, which means we don't have any other options. > Thanks, > > Josef
