On Wed, Dec 06, 2023 at 05:42:34PM +0100, Mateusz Guzik wrote: > That is to say your patchset is probably an improvement, but this > benchmark uses kernfs which is a total crapper, with code like this in > kernfs_iop_permission: > > root = kernfs_root(kn); > > down_read(&root->kernfs_iattr_rwsem); > kernfs_refresh_inode(kn, inode); > ret = generic_permission(&nop_mnt_idmap, inode, mask); > up_read(&root->kernfs_iattr_rwsem); > > > Maybe there is an easy way to dodge this, off hand I don't see one. At a guess - seqcount on kernfs nodes, bumped on metadata changes and a seqretry loop, not that this was the only problem with kernfs scalability. That might account for sysinfo side, but not the unixbench - no kernfs locks mentioned there. OTOH, we might be hitting the wall on ->i_rwsem with what it's doing...
