On Tue, May 23, 2017 at 08:09:48AM -0700, Shaohua Li wrote: > > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > > > index db5900aaa..09d093e 100644 > > > --- a/fs/kernfs/dir.c > > > +++ b/fs/kernfs/dir.c > > > @@ -634,6 +634,7 @@ static struct kernfs_node *__kernfs_new_node(struct > > > kernfs_root *root, > > > if (ret < 0) > > > goto err_out2; > > > kn->ino = ret; > > > + kn->generation = atomic_inc_return(&root->next_generation); > > > > i_generation is only supposed to be valid on a per-inode basis, so this > > global counter seems really odd. > > What's the difference between per-inode or per-super? The i_generation doesn't > need to be consecutive for an inode. I checked other fs, a lot of filesystems > implement i_generation in this way, for example, f2fs, ext4.
of course per-sb is a valid implementation, but it seems like introducing an easily avoidable bottleneck by serializing on a per-sb cacheline for each file creation. But then again it seems like kernfs already has various other per-sb contention points, so maybe it's not an issue in the end.
